The 2.5 clone papers - CCRMA

The 2.5 clone papers 

by Troels Gravesen 

troels.gravesen@danisco.com 

This is a compilation of former 2.5 clone files found at http://members.chello.se/jpo/ 

• 2.5 clone measurements and construction, v5, page 2. 

• 2.5 clone without notch filter, page 24. 

• New tweeter for the 2.5 clone, Scan Speak 9500, page 26. 

• The final 2.5 clone, the sibilance problem, page 30. 

• The “new” 8535 drivers from Scan Speak, page 37. 

• The ProAc sound, page 41. 

Only a few changes have been made to the files, thus reflecting the project progression during the last 9 months of 

work on the Response 2.5 clone. New are some comments on the ProAc sound at page 41. 

Thanks to those who started the project and gathered the basic information needed to get it all going. Thanks to 

Paulie, US, for the basic crossover design. And thanks to all who reported their project on the web (a large number 

of links can be found at http://members.chello.se/jpo/. Without the inspiration from these people, this would never 

have evolved to such a long story. 

Thanks to Darryl Nixon, Australia, for all the discussions and constructive criticism. Without the help of Darryl and 

his “One Cloner’s Journey” found at http://www.diyaudio.com , we would not have had such a fruitful discussion 

on the merits and deficiencies of speakers in general and of the 2.5 clone in particular. There will be different views 

on the “right sound” of the clones, but only your ears can tell, what is best for you and your favorite music. 

If you have any questions regarding the project, you are welcome to address troels.gravesen@danisco.com 

Please refer to page numbers on specific questions. 

Aarhus, 28 th September, 2003. 

1

2.5 clone measurements and construction, v5 

Hello, 2.5 cloners! 

Thanks to all for the huge number of mails coming in from Canada, US, Australia, Hungary, Norway, Sweden, UK, 

Finland, Russia, Greece, New Zealand, etc. as response to these pages. And I cannot thank ‘JPO’ enough for 

lending me the space on his website. Thanks to all who wrote, and commented on the work. Without these mails 

the project would have ended another place. 

In this 5 th (!) version of my file I have added the construction of bass reflex enclosures with final measurements and 

comments. Initially the drivers were mounted in transmission line cabinets available, similar in size to the 2.5s, 

making reliable measurements. 

I have had a lot of mails describing the benefits of adding the LCR circuit to the original design in order to get a 

more even frequency response but also with some regrets over loosing some of this immediate appealing 

‘technicolor’ sound of the originals. 

Some people have been confused over the increasing numbers of crossover designs; they want solutions, not 

options. For good reasons, they want to stay faithful to the original design and that’s fair enough. However, we 

cannot acquire the original drivers and we will never be able to make an exact copy of the originals. But reports 

from people comparing the clones and the originals tell us that the clone can be just as good or even better. 

The crossover modifications are fairly simple and the choice is yours! The starting point is the crossover in fig. 1. 

This design can be added a LCR notch filter, fig. 14, and you can leave it here. The latest modification I have made 

were done to fine-tune frequency and phase response and has - in my opinion – improved midrange response but 

has minor impact on the overall perceived sound. 

Fig. 1 is the basic crossover (version 1) design I have 

been testing. 

Fig 1. Basic crossover, ‘version 1’. 

And here are the MLS measurements from the 

Stereophile magazine, as a target for designing the 

crossover. 

Fig 2: Stereophile measurements. 

I was excited to see if the 2 kHz bump would appear 

as predicted from Al.M’s writing at 

http://www.geocities.com/diyproac25/. 

The bump came out beautifully as seen from the 

graphs on page 2! 

2

3 

Tweeter polarity 

My first comment to the information available is on the discussion on tweeter polarity. It is suggested you try both 

options and choose what suits you the best. 

With same polarity of woofer and tweeter there will be a major dip in frequency response, which at the same time 

can be used to fine-tune the crossover. 

100.0 

dBSPL 

TGAudio MLS - Frequency Response 29-09-02 12.44.59 

90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

200 1k 10k Hz 20k 

CH A dBSPL Unsmoothed 51.2kHz 16K Rectangular Start 1.88ms Stop 5.14ms FreqLO 306.59Hz 

red=3.3uF blue=4.5uF green=5.5uF yellow=6.8uF purple=8.3uF 

Fig 3: Polarity of tweeter. 

The tweeter certainly has to be connected with inverted polarity. 

Measurements on LP-section, inductor L2 values: 

100.0 

dBSPL 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

300 1k 10k Hz 20k 

CH A dBSPL 1/3 Octave 51.2kHz 16K Rectangular Start 2.01ms Stop 5.12ms FreqLO 322.01Hz 

red=0.83mH blue=0.68mH green=0.47 mH yellow=0.27mH purple=none 

Fig 4. Initial measurements of 8535 with 0.83, 0.68, 0.47 and 0.27 mH inductor value of 2 nd inductor in LP section. 

Not much chance of getting rid of the 2 kHz bump without a LCR circuit. I does strike me however that that lowest 

value gives a response closer to the Stereophile measurements. Making the textbook LP crossover the response is 

40dB down at 7 kHz where the target seems to more like 40 dB down at 9 kHz. 

For the time being I stayed with the 0.83 mH. The 300-1500 Hz response is rather smooth which pleases me a lot. 

CLIO 

CLIO 

180.0 

Deg 

180.0 

Deg

Significance of value of capacitor in LP section. 

100.0 

dBSPL 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

300 1k 10k Hz 20k 

Fig. 5. 


red=6.8uF blue=7.5uF green=8.3uF yellow=9uF purple=10.1uF 

The value of this capacitor makes a fine instrument of changing crossover frequency. 

Significance of C1 in LP section on full range response. 

100.0 

dBSPL 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

300 1k 10k Hz 20k 


red=3.3uF blue=4.5uF green=5.5uF yellow=6.8uF purple=8.3uF 

Fig 6. MLS 0.33 oct. smoothing. 

8.3 uF seems to be a too high value, where 5.5 to 6.8 uF looks more appropriate but as seen from the curves this 

capacitor plays an important role in determining frequency response. 

Series resistor in HP section 

I would go for the 5R6 value, giving a quite flat frequency response. Going lower may give you an immediate 

appealing sound, but may add to listening fatigue in the long run. But this can be depending on room acoustics and 

listening distance. 

CLIO 

CLIO 

180.0 

Deg 

180.0 

Deg 

4

47 ohms resistor in HP section. 

In crossover diagrams available, the 47 ohms (R3) resistor is placed at different locations. 

1. on tweeter terminals 

2. before the 4.7 uF capacitor to ground 

The graph above demonstrates the (minor) significance of this resistor placement. I’ve chosen to place the resistor 

on tweeter terminals. 

100.0 

dBSPL 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

400 1k 10k Hz 20k 


tweeter 47R red= 47R 4.7uF 

Fig 8. Tweeter, MLS, 0.33 oct smoothing. 

Construction of notch filter for the 2 KHz bump: 

A LCR notch filter was designed to smooth the frequency response between 1500 and 3000 Hz consisting of 

1.5mH(0R35)+3.3 uF+10 ohm resistor. 

Fig. 9 displays the impact on 8535 response, MLS with no smoothing. 

100.0 

dBSPL 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

300 1k 10k Hz 20k 

CH A dBSPL Unsmoothed 51.2kHz 16K Rectangular Start 2.54ms Stop 5.61ms FreqLO 326.11Hz 

Fig.9. LP section +/- LCR and full range response with LCR. 

Notice that crossover target is only slightly affected and can easily be adjusted with C1. Fig.5. 

CLIO 

CLIO 

180.0 

Deg 

180.0 

Deg 

5

LCR impact on full range response 

100.0 

dBSPL 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

400 1k 10k Hz 20k 


Fig.10. Full range response +/- LCR, 0.33 oct. smoothing. 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


Fig. 11. Full range response + LCR, same and reverse polarity (no smoothing). 1 meter distance, tweeter height. 

CLIO 

CLIO 

180.0 

Deg 

180.0 

Deg 

6

Significance of LCR on cumulative spectral decay. 

TGAudio Waterfall 06-10-02 17.59.41 

0 

dB 

-5 

-10 

-15 

-20 

400 1k Hz 10k 20k CLIO 

Cumulative Spectral Decay 

Fig.12. 20 dB range CSD, without notch filter. 

TGAudio Waterfall 06-10-02 17.58.05 

0 

dB 

-5 

-10 

-15 

-20 

400 1k Hz 10k 20k CLIO 

Cumulative Spectral Decay 

Fig.13. 20 dB range CSD, with notch filter. 

The impact of the notch filter speaks for itself. With the LCR circuit in place an impressive + 1 dB frequency 

response is achieved between 300 and 4000 Hz, and the lack of the 2 kHz bump is clearly audible, where especially 

female voices gets a natural balance and acoustic guitars which may sound almost too good with the bump, now are 

presented with a much more realistic timbre. Listening to pink noise on the 8535 +/- LCR filter strongly suggests 

we get rid of the bump. Read Lynn Olson (Ariel) on the use of pink noise! http://www.alohaaudio.com/Arieltxt2.html#top 

And best of all, the 8535 does not loose its fresh and crisp presentation. The sound of the 8535 is hard to describe 

(isn’t sound always?), but certainly this is a very lucky/clever combination of the right matrix of paper pulp and 

carbon fiber, the right cone size and weight (the cone is more flexible that the 8545), voice coil dimensions, magnet 

size, all giving a smooth roll off characteristic and simplifying crossover design. 

2.7 

2.7 

1.8 

1.8 

0.9 

0.9 

0.0 

ms 

0.0 

ms 

7

Modified crossover, basic design + notch filter (version 2): 

Fig 14. Version 2 crossover. 

Fine tuning of crossover, version 3: 

In order to improve frequency and phase response I have modified the crossover and it looks like this. Red 

indicates changes. 

Fig 15. Version 3 crossover. 

Some people have made complaints on the crossover presentation and here is a more graphic presentation for biwiring. 

The components in the LCR circuit can be put together in any order, 

it does not matter! And be sure to have a decent distance between inductors - like 5 cm, in order to reduce 

interaction. 

8

Fig.16. 

System response with Fig. 14 (version 3) crossover: 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

300 1k 10k Hz 20k 


red=sensitivity, 2.83 V AC, 1 meter blue=min fase 

Fig.17. System response, version 3. 

Red/blue=left and right speaker. 

CLIO 

180.0 

Deg 

9

System impedance 

50.0 

Ohm 

TGAudio Sinusoidal 29-09-02 14.45.18 

40.0 108.0 

30.0 36.0 

20.0 -36.0 

10.0 -108.0 

0.0 -180.0 

10 100 1k 10k Hz 20k 

File: imp full range.sini 

CH A Ohm Unsmoothed Stepped Delay [ms] 0.000 Dist Rise [dB] 30.00 

Fig. 18. Impedance of full range (without notch filter) system. 

Not that much different from the Stereophile measurement, although it’s difficult to read the scale on the 

Stereophile scanning. 

The high damping of the lower impedance peak in the bass is caused by the stuffing of the transmission line and 

should be disregarded in this context. 

ScanSpeak 18W/8535-00 

Finally, here are the TS parameters of my 8535s: The data for the two units are remarkably alike, but the Qt is 

significantly higher that the promised 0.4! 

ScanSpeak data: Vas=69 litres, Qt= 0.38 and Fs= 26 Hz. 

My measurements: Vas = 44 litres, Qts= 0.52 and Fs= 34 Hz. 

ScanSpeak is using constant current method at high level, 36 mA, which may account for lack of correlation. 

My speaker calculation software says ~ 42 liters from the SS-data, my measurements suggests ~ 67 liters. Another 

software tells me this unit is best suited for a closed box! 

MANUFACTURER ScanSpeak ScanSpeak 

MODEL 18W8535-I 18W8535-II 

DATE 20-09-2002 20-09-2002 

Fs 33.9 34.8 

Qms 2.92 2.93 

Qes 0.63 0.63 

Qts 0.52 0.52 

VAS 43.9 43.1 

Mms 14.4 13.9 

BL 5.34 5.36 

dBSPL 86.3 86.6 

SD 0.0143 0.0143 

Re 5.88 5.94 

Fig.19. TS data. 

These data were generated with my CLIO measurement system set at 0dB level. Adding another 0.4 ohm resistance 

(from inductors) in series with the woofer makes things even worse. The magnet on the 8535 seems to be too small 

for a 33-liter cabinet. Object for some tweaking! 

CLIO 

180.0 

Deg 

10

TS parameters at different measuring level: 

measuring level +10dB 0dB -10dB -20dB 

MANUFACTURER scanspeak scanspeak scanspeak scanspeak 

MODEL 18W8535 18W8535 18W8535 18W8535 

DATE 30-01-2003 30-01-2003 30-01-2003 30-01-2003 

Fs 32.37 35.16 36.65 37.35 

Re 5.86 5.86 5.86 5.86 

Rms 1.15 1.00 1.01 0.92 

Qms 2.64 2.96 3.47 3.72 

Qes 0.54 0.60 0.66 0.68 

Qts 0.45 0.50 0.55 0.58 

Cms 1.62 1.53 1.24 1.24 

Mms 14.96 13.41 15.24 14.68 

BL 5.74 5.36 5.60 5.44 

VAS 46.25 43.71 35.40 35.40 

Fig.21 

Series filters 

At http://audioclone.free.fr/ two series filters have been proposed and I have tried to wire up the circuits, and here 

are my measurements: 

Version 1: 

Fig. 22. Series filter #1. 

First of all a RC circuit has been placed at the crossover terminals which is a strange feature as it generally lowers 

the sensitivity of the whole system. I’ll show later the impact of this on frequency response. 

11

Frequency response, series filter #1, no RC circuit: 

100.0 

dBSPL 


90.0 36.0 

80.0 -36.0 

70.0 -108.0 

60.0 -180.0 

50.0 -252.0 

200 1k 10k Hz 20k 

File: 95 cm MLS.mls 


red=95 cm hight blue=min phase 

Fig.23. Series filter #1, 1 meter distance, tweeter height. Red=freq.resp. blue=min.phase. 

When I first looked at this I thought I’d done a serious mistake and checked the setup several times. Couldn’t fine 

anything wrong. Minimum phase indicates serious problems and I tried same polarity of woofer and tweeter: 

Frequency response, series filter #1, no RC circuit, same polarity: 

100.0 

dBSPL 


90.0 36.0 

80.0 -36.0 

70.0 -108.0 

60.0 -180.0 

50.0 -252.0 

200 1k 10k Hz 20k 


File: 95 cm MLS-same polarity.mls 

red=95 cm hight blue=min phase same polarity 

Fig.24. Series filter #1, same pol. Red = freq.resp., blue=min.phase 

Well, at least the major dip in frequency response at 2 kHz was gone, but the 2 kHz bump came to life again and 

min. phase still isn’t to pretty. 

I suppose the series filter was constructed with the intention of keeping inverted polarity of the drivers, so I went 

back to this and tried different measuring heights. 

Next is the response measured at 1 meter distance, microphone between tweeter and woofer: 

CLIO 

CLIO 

108.0 

Deg 

108.0 

Deg 

12

100.0 

dBSPL 


90.0 36.0 

80.0 -36.0 

70.0 -108.0 

60.0 -180.0 

50.0 -252.0 

200 1k 10k Hz 20k 

File: 91 cm MLS.mls 


red=91 cm hight blue=min phase 

Fig.25, series filter #1, 1 meter distance, mic. between tweeter and woofer. Red=freq.resp., blue=min.phase. 

This turned out even worse, almost an 180 o phase shift at 2.5 kHz. 

I went back to measuring at tweeter height! 

Series filter #2, no RC circuit 

In this setup a 1 mH coil is introduced across the tweeter and there are minor modifications to the other 

components. 

Fig. 26. Series filter #2. 

CLIO 

108.0 

Deg 

13

Frequency response of series filter #2, no RC circuit: 

100.0 

dBSPL 


90.0 36.0 

80.0 -36.0 

70.0 -108.0 

60.0 -180.0 

50.0 -252.0 

200 1k 10k Hz 20k 

File: series v2.mls 


red= v2 blue=min phase 

Fig.27. Series filter #2, no RC. Red= freq.resp., blue=min.phase. 

The serious dip in response at 2.3 kHz has been reduced slightly, but this is far from being an acceptable frequency 

response. And still there are serious phase problems. 

Impact of RC circuit on system response, series filter v.2: 

100.0 

dBSPL 


90.0 36.0 

80.0 -36.0 

70.0 -108.0 

60.0 -180.0 

50.0 -252.0 

200 1k 10k Hz 20k 


File: plus-minus-RC.mls 

inverted polarity red=tweeter hight, no RC blue=tweeter hight, +RC 

Fig 28, System response, series filter #2, with/without RC circuit. Blue = with RC. 

The system response is generally lowered by 2 dB. 

The system response of the 2.5 clone is around 83 dB/2.83 V/1meter, which is pretty low. No reason to burn more 

energy in the RC circuit. 

CLIO 

CLIO 

108.0 

Deg 

108.0 

Deg 

14

Impedance of system with series filter #2, +/- RC circuit: 

50.0 

Ohm 

TGAudio Sinusoidal 08-12-02 00.24.24 

40.0 108.0 

30.0 36.0 

20.0 -36.0 

10.0 -108.0 

0.0 -180.0 

10 100 1k 10k Hz 20k 

File: imp v2+RC.sini 

CH A Ohm Unsmoothed Stepped Delay [ms] 0.000 Dist Rise [dB] 30.00 

red:v2 no RC blue:v2 +RC 

Fig. 29. Series filter, impedance, +/- RC circuit. 

Indeed the impedance is flattened to around 4 ohm above 100 Hz. 

My only comment to the RC circuit is that this must be a mistake. 

Well, those who might have been annoyed with the 2 kHz bump in the original design certainly eliminate this 

problem with the series filter, but this seems to introduce new and more serious problems. Frequency and phase 

responses are unacceptable and serious tweaking is necessary to get it right. 

The problem with series filters is that it’s difficult to measure the response of the individual drivers. John 

Kreskovskij has a method, but I haven’t tried it yet. 

http://www.geocities.com/kreskovs/Series-1.html 

I have only briefly done listening tests with the series filter but I find the dip at 2 kHz clearly audible and the 

tweeter far to loud for my taste. 

Replacing the drivers with 8 ohm resistors is not strictly correct but can give us an idea of what is going on. 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


drivers replaced by 8R2 resistors 

Fig. 30. 

Red= frequency response of system with series filter. 

Blue= 8535 woofer with series filter. 

Green= 8513 tweeter with series filter. 

Purple= with resistor and capacitor for tweeter inverted, which gives a better response because now the capacitor 

‘sees’ a much more reasonable impedance. 

Yellow = system response with this modification. 

CLIO 

CLIO 

180.0 

Deg 

180.0 

Deg 

15

Fig 31. Part of series filter with inverted C and R for tweeter. 

With the suggested design the tweeter reaches down to 1500 Hz giving serious phase problems in the crossover 

region. 

Inverting the resistor and capacitor helps a lot, but there are months of work to get it right! 

Conclusion on series filters: 

The series filter has a less than acceptable frequency response, serious phase problems and cannot be 

recommended. 

And don’t place a RC circuit on top of the whole crossover, this way you will just burn energy and reduce system 

efficiency, which is so much needed. 

16

Construction of bass reflex cabinets: 

A lot of cabinet construction papers have been published and I won’t go into much detail about this. 

I have maintained the internal volume but outer dimensions have been changed to 20 x 26.5 x 100 cm and the 

bottom plate have been lifted to give room for the crossover to be placed externally. This way it’s easy to make 

changes, and the components are not affected by vibration from the driver. The tweeter has it’s own sealed back 

chamber in order to reduce vibrations from the woofer. Cross bracing has been added to reduce cabinet resonance. 

Cabinets are constructed from 20 mm pre-veneered MDF and front panels are 25 mm (15 mm solid mahogany + 10 

mm MDF). Internal bracing is 10 mm MDF. 

Fig 32. Cabinets partly assembled. 

All walls are damped with 10 mm heavy polyester foam (glued to the panels) and a mixture of polyester and lambs 

wool available from Monacor is used for further damping. 

Right behind the 8535 several layers of the lambs wool is placed in order to reduce standing waves hitting back on 

the membrane. 

Deflex damping material is to my knowledge not available in Denmark (?). 

Some more pictures: 

Fig.33, 2.5-crossover. 

Cored 1.8 mH coil and air-cored 0.47 mH, both

Fig. 34, front plate. 

Fig.35, back side of front plate. 

Fig.36, damping material. 

Fig.37, CO at base plate. 

18

At last, the final cabinets with drivers, first play in my workshop; why is it that I after just a couple of months 

forget how many hours it takes to build a pair of cabinets!? 

Fig 38. First time setup in my workshop. 

Crossovers, the never ending story… 

- and short presentation of features: 

1. The ‘original’ design, version 1 (fig.1) 

You are likely to have a major bump at 2 kHz, which sounds very well on certain recordings but makes voices and 

violins intolerable. Darryl from Australia calls this the ‘technicolor sound’ and that is just what it is. 

2. Original design + LCR, version 2 (fig 14) 

You get rid of the 2 kHz bump and can enjoy a wider spectrum of recordings. Enhanced three-dimensionality and 

lots of space. 

3. Modified crossover + modified LCR, version 3 (fig15) 

An even flatter frequency and improved phase response in the critical upper midrange. The choice is yours. 

Having finished my bass reflex enclosures I have wired up the three crossover (CO) versions again and was excited 

to see whether I could reproduce my measuring results 2-3 months ago! And it didn’t turn out too bad. All 

measurements performed at 1 meter distance, tweeter height. 

The Stereophile review suggests we have a crossover point of 3200-3300 Hz, where the version 1 gives 3000-3100 

Hz, slightly below the original. The version 3 displays a crossover point of 3350 Hz. However, no need to be exited 

about +/- 100 Hz. The aim of the v3 crossover was to create a less steep roll-off as seen on the Stereophile 

measurements. The 8535 driver is down 40-45dB at 8.5 kHz where we - with the v1 crossover - reach this level 

already at 7 kHz. It has been suggested that the OEM-8535 has less carbon fiber and a more flexible membrane 

than the ‘DIY’ units. This could mean enhanced high frequency response and a smoother roll-of performance. The 

problem with having a notch filter at 2 kHz is that it is so close to the crossover point, that it’s impact is stretched 

over the crossover region. I have tried a notch-filter acting exactly in the 1500-2500 Hz region, but this didn’t 

perform well. 

Fig. 39 and fig. 40 displays the 8535 performance with the v2 and v3 filter +/- notch filter. 

Fig. 41 and fig. 42 displays the overall performance of drivers with same and inverted polarity and tells us that we 

have a very good phase correlation between drivers in both cases. The v3 has a more symmetrical >20 dB null at 

crossover point with same polarity. The 8535 with the v2 CO has a very abrupt, linear and steep roll-off behavior. 

19

90.0 

dBSPL 

MLS - Frequency Response 14-02-03 18.35.47 

80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

300 1k 10k Hz 20k 

CH A dBSPL 1/3 Octave 51.2kHz 16K Rectangular Start 2.56ms Stop 5.53ms FreqLO 336.84Hz 

2.5 crossover v2 1.8mH/7.4uF/0.83mH 3.3uF/10R/1.5mH 

Fig. 39. 2.5 crossover, v2, red: + LCR, blue: no LCR 

90.0 

dBSPL 

CLIO 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

300 1k 10k Hz 20k 


crossover v2 LP:1.8mH/6.8uF/0.83mH LCR:3.3uF/10R/1.5mH HP:5R6-3.3uF/0.25mH/4.7uF-47R CO-point=3100Hz reverse/same pola 

Fig. 41. 2.5 crossover, v2, all drivers, polarity 

Crossover point = 3100 Hz 

0.33 oct. Smoothing. Same polarity, no smoothing 

Frequency response of 2.5 with CO v2 and v3 

90.0 

dBSPL 

CLIO 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

300 1k 10k Hz 20k 


2.5 crossover v2 and v3 full range response and min. phase green/purple=v2 red/blue=v3 

Fig. 43.Green/purple(min.ph) = v2, Red/blue(min.ph) 

= v3 

CLIO 

180.0 

Deg 

180.0 

Deg 

180.0 

Deg 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 


2.5 crossover v3 1.8mH/6.8uF/0.47mH 2.2uF/10R/1.5mH 

20 

40.0 -180.0 

200 1k 10k Hz 20k 

Fig. 40. 2.5 crossover, v3, red: + LCR, blue: no LCR 

90.0 

dBSPL 

CLIO 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

300 1k 10k Hz 20k 

CH A dBSPL Unsmoothed 51.2kHz 16K Rectangular Start 2.56ms Stop 5.53ms FreqLO 336.84Hz 

crossover v2 LP:1.8mH/6.8uF/0.47mH LCR:2.2uF/10R/1.5mH HP:5R6-3.9uF/0.22mH/4.7uF-47R CO-point=3400Hz reverse/same pola 

Fig.42. 2.5 crossover, v3, all drivers, polarity 

Crossover point = 3350 Hz 

0.33 oct. Smoothing. Same polarity, no smoothing 

Frequency response of CO v3 at 1 and 2 meters 

100.0 

dBSPL 

CLIO 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

300 1k 10k Hz 20k 


2.5 response tweeter height red=1 meter blue=2 meter purple=same pol. 2 m, 2.5 cm above tweeter height 

Fig. 44. Red=1m, blue=2m, purple=same pol. 

CLIO 

180.0 

Deg 

180.0 

Deg 

180.0 

Deg

100.0 

dBSPL 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

300 1k 10k Hz 20k 


blue=left speaker red=right speaker sensitivity 2.83Vrms 

Fig.45. Freq. Response left and right speaker. 

Sensitivity at 1 meter, 2.83 Vrms, ~ 83 dB. 

For comparison here are fresh Rogers LS3/5a (11 

ohm version) frequency response curves, with and 

without front grille. A legendary loudspeaker with 

phase problems in the crossover region that today 

would make any home constructor ashamed of 

himself. I keep these shoeboxes to remind myself of 

not overemphasizing any single parameter in 

loudspeaker construction because they sound so 

good. 

100.0 

dBSPL 

CLIO 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

300 1k 10k Hz 20k 


LS35A red:+front blue:-front 

Fig.46. Rogers LS3/5a, 11 ohm version, 1989. 

100.0 

dBSPL 

CLIO 


90.0 1.000 

80.0 0.600 

70.0 0.200 

60.0 -0.200 

50.0 -0.600 

300 1k 10k Hz 20k 


red=0 blue=10 green=20 purple=30 

Fig. 47. CO v3 horizontal response, 

0(red),10(blue),20(green)30 o (purple) 

CLIO 

180.0 

Deg 

180.0 

Deg 

1.400 

ms 

21 

Well, whether you choose v2 or v3 crossover you 

will get a great speaker in any case. 

Be sure to use the right component values in either 

case. The most important components are the 

capacitor in the LP section, 7.4 uF for v2 and 6.8 uF 

for V3, the coil in the HP section, 0.25 mH for v2 and 

0.22 mH for v3 and finally the capacitor in the LCR 

circuit, 3.3 uF for v2 and 2.2 uF for v3. 

I am very happy for the evaluation given by Darryl in 

Australia and with his permission, here are his 

comments: 

I finally got around to experimenting with resistor 

value increases in the notch filter, which you 

suggested might restore some of the "life" or 

"technicolour" sound to your latest (final?) crossover 

version. 

Increasing the resistor to 12 ohms does do this to 

some small extent I guess, but any greater value 

begins to re-introduce the upper midrange glare 

quite audibly (to my ears, anyway). All things 

considered, I still prefer the sound with the 10 ohm 

value, i.e. an optimally flat response in the 2 KHz 

area. 

I did find that reducing the resistor on the tweeter 

from 5.6 ohms back down to 5 ohms produced quite 

an improvement - I should have tried this before - 

and restored much of that distinctive Proac sound, 

more so than I would have expected. (With the 

standard (Jacq) crossover + notch filter, I preferred 

the 5.6 ohms you recommend.) Increasing the tweeter 

output in your latest crossover makes it a lot harder 

to choose between the two versions. Even with 

increased tweeter level, sibilance is still better 

controlled and the midrange sounds more realistic 

than it does with the Jacq version + notch filter. I 

think I'll stay with your latest version for the time 

being, albeit with slightly increased treble. That 

change has swung things the other way for me. It 

seems a good compromise in my system, and 90 per 

cent of the time it sounds wonderful. 

Incidentally, the listening tests I've been carrying out 

have been with a Dynaco PAS3X/Stereo 70 valve 

preamp and amp. I also have a Sugden C51/P51 

solid state combo, but it's off for repair at the 

moment.

I was curious to see what would happen with a mid-fi 

solid state amp, so borrowed a friend's NAD 1155 

preamp and Rotel RB-981 power amp. There is no 

doubt in my mind that the Proac is best suited to 

valve amplification. With this solid state set-up, there 

was a definite "hardness" in the midrange which was 

easily provoked by the wrong recording. Sibilance 

also became more of a problem. The sound was also 

quite "dry" and occasionally harsh, though bass 

depth and definition was astoundingly good. (A 

Superphon Revelation Basic Preamp did improve 

things at the top end.) Nevertheless, the speaker 

seemed a lot more tolerant of this set-up with your 

latest crossover than with the Jacq + notch filter. My 

own Sugden (although no longer young) works far 

better, having more valve-like warmth and a much 

superior presentation all round, though not as good 

as the Dynaco. 

To my mind, the Proac Response 2.5 is a seriously 

good but extremely fussy speaker, easily provoked 

into sounding less than wonderful. The bass-mid is 

very transparent to the source, and can easily stray 

into hardness with inadequate SS amplification, discreproduction 

equipment or poor recordings. (I do 

wonder whether that hardness is in part due to cone 

break-up, albeit at a low level thanks to your notch 

filter.) 

Another problem is the tweeter, which can easily 

stray into excessive sibilance with the wrong 

recording, though your latest crossover mods go a 

long way towards eliminating this. Yet another 

problem is a lack of energy in the lower 

midrange/upper bass, which seems to be roomboundary 

related. Careful positioning and a warmsounding 

amp can minimise this, but it seems 

impossible to cure completely. 

I guess I'm being over-critical, given the Proac's 

price-point. – and all "high-end" equipment is fussy. 

Nevertheless, this is the best speaker I have ever 

owned and pretty easy to live with - and it now works 

very well in my system. I just wonder how many 

people out there are disappointed due to matching 

problems in their systems! 

Final evaluation 

This is probably the most tough part of it all having 

to express sonic qualities in a foreign language. 

But I’ll give it a shot…. 

This is probably my 5 th floorstander of this design 

being bass reflex or transmissionline constructions, 

all two-way designs of approx. 20x25x100 cm in size 

with SS8545+9500, Vifa PL18+XT25, Vifa 

M18WO+D27, etc. 

My setup consists of a ROTEL CD modified with 

goodies from LCAudio, a CT101 audio buffer from 

22 

DanishAudioConnecT (www.dact.com) and a 

LCAudio, non-feedback 120 W power amplifier, 

Millenium edition (www.lcaudio.dk). 

Listening sessions, version 3 crossover. 

First disc was Charlie Haden & Pat Metheny: 

Missiouri Sky. 

It's been a couple of months since I had my initial 

transmission lines running and the final setup with 

the reflex boxes by far exceeded my expectations. 

The bass is significantly better in the reflex boxes and 

I had to remove things from my living room that do 

not use to rattle with my ‘reference’ system! I can't 

believe they go this deep! A tiny 6½" woofer! The 

midrange is clear, crisp and transparent and listening 

to acoustic music it's very, very good. On track two 

the guitar is very closely miked with a lot of low-end 

information and the bass attack is most impressive. 

The tonal balance seems to favor the highs and 

listening to female jazz-singers, strings and big-band 

music was not so impressive! ‘S’-sounds and ‘T’sounds 

are much to pronounced and the tonal balance 

of violins are simply not correct compared to my 

‘reference’ where voices can be played at loud 

volume without distress. The phenomenon is called 

sibilance! 

Tried to unplug the tweeter and played the 8535 at 

loud levels and everything sounds fine except that 

you miss the tweeter. The problem doesn’t seem to 

come from here. 

Another comment from Darryl: 

Do you also find a lack of energy in the lower 

midrange/upper bass? My own clones sound 

beautifully warm provided there are deep lows in the 

recording, but if not, they can sound quite "dry". 

Yes and no. I can’t say that I have experienced any 

lack of energy or level in upper bass register and I 

believe actual room acoustics plays an important role 

here. On the other hand I like a speaker that has a 

very dry sound. I’ve done a lot to reduce vibrations in 

my cabinets and this probably helps a lot in providing 

a dry sound. I don’t feel any vibrations on sides, front 

and back of the cabinet, but strangely enough on the 

top plate and I’ll have to ad additional material to 

eliminate this.

Let’s take another look at the frequency response: 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


Fig.48. Value of tweeter series resistor 

Green=5R6 

Yellow=8R2 (sorry for the yellow, hope it’s visible) 

Purple=10R 

Usually I try to target the BBC-dip curve, giving a ~2 

dB dip in the upper midrange/lower highs usually 

giving a slightly more distant perspective, but an 

overall more balanced sound. The response of the 

clones do not exactly meet this criteria. We have a 

rather flat midrange response and it better be good 

with this level. 

Fig. 48 graphs are showing the response at 2.83Vrms 

(measured at speaker terminals) and from 0.3-3.5 

kHz we have a very flat response of +/- 1 dB. Quite 

impressive. But from 4-17 kHz we are least 2 dB 

higher and from another construction I learned that 

this could make a world of difference. I have worked 

a lot with the 8512 tweeter supplementing an ETON 

4-300 midrange and this – when properly balanced – 

works very well. The 4-300 is a very revealing 

midrange driver and matching this driver with a 

slightly too highly pitched tweeter makes it 

intolerable to listen to. 

Maybe the 8512 and –13 isn’t that well suited to 

work with the much larger 8535 woofer/midrange 

cone. I would like to try the HIQUPHON OW1tweeter 

without magnetic oil (and probably more 

heavily coated) and produced to very close tolerances 

with reported low distortion and coloration and an 

impressive CSD. 

Changing the tweeter series resistor to 8R2 or 10R 

seems to correct things and I stayed with 8R2 

because with 10R I would have to go through another 

fine-tuning of the HP section because it changes the 

crossover point to 3.7 kHz and creates a 1.5 dB dip at 

~3.5 kHz. 

It helped a great deal on the above mentioned 

problems although there are still recordings were they 

fall short compared to my ‘reference’. 

CLIO 

180.0 

Deg 

23 

It’s a gut feeling, that the 8513 may not be the one 

to pick if you want a more true presentation of the 

upper register of most instruments and voices. It has 

some intrinsic values in terms of speed and 

‘sparkling’ sound, and possibly we can turn this 

speaker into something that will split constructors 

into two groups. One group that wants to stay true to 

the original design with its limitations in terms of not 

being able to obtain the ‘real’ OEM-drivers and 

another group that will take the best of the 8535’s 

deep bass capabilities and midrange clarity and 

combine it with a tweeter that supplements these 

virtues with more fidelity. 

Best regards 

Troels Gravesen 


PS, 30.03.2003 

Have tried the OWI tweeters and except for size and 

sensitivity they can immediately replace the 8513, 

but the response turns out even flatter than with the 

8513s and the sound wasn’t so good. After some 

tweaking, I decided this would require a new 

crossover and tempting as it was, this is not the time. 

The OWIs measures the best I have ever experienced. 

Ruler flat from 1 kHz to 20 kHz! Can’t wait to 

incorporate these in some future design.

The 2.5 clone without notch filter 

Sometimes it takes a journey to get back to your 

starting point and see what is the real problem in 

front of you. 

This being the case with the 2.5 clone and the 2 kHz 

bump created by the 8535 driver itself and the 

crossover topology. One person at diyaudio.com 

working with active crossovers for the clone even 

predicted that there should be a bump at 2 kHz 

derived from the crossover. 

In my latest paper at http://members.chello.se/jpo/ 

(New 2.5 clone tweeter, crossover and speaker 

setup) I have constructed a new crossover for 

implementing the ScanSpeak D2905-9500 tweeter. 

By starting all over again with the crossover it was 

obvious to experiment with the Q of the parallel 

capacitor in the LP-section. In order to get the target 

point of crossover and the target roll-off 

characteristic a RC circuit was added. It appeared that 

no notch filter was needed. 

When this was done it was obvious to try to apply 

this approach to the 8535+8513 drivers for those who 

want to maintain the 8513 tweeter. 

Initial measurements of 8535 driver: 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


red= +1.8 mH blue= +1.8mH/7.4uF/0.83mH green=+1.8mH/6.8uF+3R3/0.47 mH 

Fig.1. 8535 driver SPL response, 0.33 oct. 

smoothing. 

Blue = 8535 driver with v1 crossover: 1.8 mH//47R + 

7.4 uF + 0.83 mH 

Red = 8535 driver + 1.8 mH 

Green = 8535 driver with new crossover: 1.8mH + 

(6.8uF+3R3) + 0.47 mH 

As seen from the graphs it is possible to eliminate the 

notch filter by adding a resistor to the capacitor. That 

simple! 

And the point of crossover can still be adjusted by the 

capacitor value (data not shown). 

I have tried to maintain all component values in the 

new design to minimise the cost of the change. This 

CLIO 

180.0 

Deg 

24 

modification refers to the ‘version 3’ crossover 

found in ‘2.5 clone measurements and construction, 

v5’ at http://members.chello.se/jpo/. 

And it implies the use of DAMAR coating as 

described in 8535+9500 paper. However, I’m 

confident that this modification will also work fine 

without the DAMAR coating. 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


red= +1.8 mH blue= +(1.8mH-47R)/(7.4uF)/(0.83mH) green=+(1.8mH-47R)/(6.8uF+3R3)/(0.47 mH) 

Fig.2. Driver response, 0.33 oct. smoothing. 

As seen from the graphs the result is a smooth 

midrange response, and the level can be adjusted to 

personal taste by changing the value of the resistor in 

the in LP section, fig. 3. 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 

CLIO 


green=2R2 red=3R3 blue=4R7 

Fig.3. Value of R in LP section. 

Green = 3R3, red = 4R7, blue = 5R6. I recommend 

3R3. 

Crossover changes: 

• The 47R resistor parallel to the 1.8 mH 

inductor removed. 

• The 6.8 uF capacitor is added a 3.3 ohm 

resistor. 

• LCR notch filter is removed. 

• No changes to the HP-section. 

180.0 

Deg 

CLIO 

180.0 

Deg

2.5 clone crossover, version 6. Tweeter level 

Fig. 4. crossover, v6. 

(I’m sorry for having to call this version #6, but there 

have been a number of designs in between, and I 

have to keep track of all changes). 

Here’s a graphic presentation for bi-wiring: 

Fig.5, crossover, v6 

90.0 

dBSPL 

25 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


red=4R7 blue=5R6 green=8R2 

Fig.6. Tweeter series resistor, red = 5R6, blue = 6R8, 

green = 8R2. I use 8R2. 

The choice is yours. 

CLIO 

180.0 

Deg

New tweeter for the 2.5 clone 

After introducing the 2 kHz notch filter to the 

original crossover (v2) design and also introducing a 

slightly modified filter (v3) in order to smooth 

frequency and phase response in the upper midrange, 

still people have been complaining about the sibilant 

nature of the upper registers. I have defended the 

8513 tweeter, being such a proven design, and have 

hesitated to make any changes to the tweeter as this 

would most certainly for good take us away from the 

ProAc Response 2.5 sound with its strengths and 

weaknesses. 

However, I cannot ignore the fact that a number of 

my recordings linger on my CD-shelf as long as the 

clones are in place in my living room, this mostly 

being records of vocal music. 

But first a short story on the tweaks that have been 

conducted in order to get to the decision of 

introducing a new tweeter. 

DAMAR coating 

A series of near field measurements of the 8535 were 

done in order to localize cone break-up and not 

surprisingly the dust cap is responsible for some 

serious cone break-ups that create a significant bump 

at 2 kHz (fig. 1) (same place as the bump created by 

the crossover). 

Two layers of DAMAR coating were applied to the 

center dome and this to some extent smoothed the 

frequency response in the upper midrange (fig. 2) and 

also above 10 kHz. Subjectively this had a positive 

effect on the overall perceived sound. 

Damping the 8535 Dust Cap (diyaudio.com), Darryl 

Nixon and Troels Gravesen. 

Recent experiments by Troels Gravesen have 

demonstrated that there are advantages in applying 

damping to the dust cap of the clone's 8535 mid-bass 

driver. Troels has been working on the resonance 

problems of the 8535 which he found has "a major 

intrinsic bump at 3 KHz". In Troels' words, “. . . the 

coating seems to remove some edginess in the 

midrange with a more smooth performance and 

tolerance towards difficult recordings". 

The substance used is Damar varnish, which can be 

obtained from artists' supply shops. The picture 

attached is from Troels and is of Damar as sold in 

Denmark. The following is reported with Troels' 

permission, together with quotes from his e-mails to 

me. 

"As a start you may apply a coating until the dust cap 

is soaked and leave it there as long as it is not 

applied outside the dust cap. The effect should be 

there in a couple of hours . . . 

26 

"At the beginning of applying the DAMAR the 

somewhat porous dust cap readily absorbs the 

varnish and I continued to apply DAMAR until the 

surface appeared shining. This doesn't mean 'flooded' 

with liquid, so 'soaked' may be a little overstated. 

Actually the amount of DAMAR applied is moderate. 

I should have applied it in mikrolitre quantities to 

give recommendations. However, after drying the 

application is hardly visible. After 1 hour I repeated 

the application with a final coat of 'less than first 

time'. After 1 week I don't measure altered 

performance, so I guess the treatment is stable over 

time. If the coating is to be removed the dust cap is 

soaked with turpentine and absorbed with Kleenex 

tissue." 

The varnish sold under the "Damar" brand name in 

my own country is produced by the company Art 

Spectrum, and the 100mL bottle I obtained looks 

physically different. Also, the consistency of the 

substance is obviously thicker than that sold in 

Denmark. Applying it as Troels recommended did not 

produce the same visual results he described. The 

varnish did not really soak into the dust cap as I 

applied it, but produced a shiny appearance from the 

outset. Nevertheless, I went ahead and applied a 

moderate amount. It took several hours to dry, 

though it remained slightly sticky in places even 18 

hours later. (Mind you, it had been raining here for 

several days, so that may explain the drying time.) It 

eventually soaked in to a large extent, though there 

were still some shiny patches. I reported this to 

Troels and he recommended the following: 

"If your Damar batch seems to be rather thick I'd 

hesitate to apply a second layer of coating. Maybe 

one additional layer at the 'center of the centerdome', 

like 2 cm diameter. Uneven distribution of coating is 

usually a good thing in disturbing resonances." 

My listening tests produced similar results to Troels'. 

There is a small but definite reduction in midrange 

edginess, giving a slightly cleaner sound in what I 

consider to be the clone's main problem area. This 

benefits "difficult" recordings in particular, so if you 

are troubled by the clones' midrange this is a highly 

recommended mod. Just don't expect miracles! The 

effect is subtle. 

The important thing is that you don't apply too much 

(though the coating is reasonably easy to remove 

with turpentine if you do) – and that you DON'T get 

any on the cone itself. (Troels did try damping the 

cone with Damar, but the results were very negative.)

110.0 

dBSPL 


100.0 108.0 

90.0 36.0 

80.0 -36.0 

70.0 -108.0 

60.0 -180.0 

200 1k 10k Hz 20k 


File: 8535-1.8mH.mls 

Fig.1, red = 8535 in cabinet, no crossover. Blue = 1.8 

mH in series with 8535. No smoothing. 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


Fig.2. Red = 8535 after DAMAR coating, no filter. 

Blue = 8535 after DAMAR coating + 1.8 mH. 

Identifying the source of sibilance 

First the clones were cut off below 100 Hz by a 6 dB 

filter and supplemented by a subwoofer in order to 

significantly reduce cone movement and ease the 

burden put on the 8535 by having to reproduce 

everything from 30 Hz to 3 kHz. 

This did not in any way reduce the sibilant nature of 

the highs. Excessive cone movement does not seem 

to be a severe limiting factor for the 8535 in order to 

truthfully reproduce the sensitive midrange except 

when played at very high level. 

Secondly a 3-way construction was tried introducing 

a Vifa PL11MH coated midrange at 500–3000 Hz. 

This is indeed a very good midrange and I wouldn’t 

CLIO 

180.0 

Deg 

CLIO 

180.0 

Deg 

27 

hesitate to use this in some other construction. 

This did not – much to my surprise – in any way 

change the sibilant nature of the highs! After this 

there was only one thing left to do: ‘Thanks to the 

8513 tweeter for all the hours we have spent together, 

but out you go!’ 

Having a pair of ScanSpeak 9500s, this was an 

obvious choice for a new pair of tweeters. 

I have removed the magnetic oil in the voice coil gap 

of the 9500s. Otherwise no tweaks. 

Construction of a new crossover 

LP-section: You can reuse most of your components 

from the v3 crossover in this new filter. The 1.8 and 

0.47 mH coils are the same. The capacitor has been 

raised to 8.3 uF (6.8+1.5) and a 2R2 resistor has been 

added to the capacitor giving a smooth roll-off for the 

8535. The point of crossover is intended to be around 

3 kHz, as I’m now confident that the 8535 will do 

well all the way to this point and I want to maintain 

the 8535 handling as much of the midrange as 

possible. 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


Fig. 3. 8535 roll-off with various filters: 

Red = 1.8 mH + 8.3 uF + 0.83 mH 

Blue = 1.8 mH + 8.3 uF + 0.47 mH 

Green = 1.8 mH + (8.3 uF+2R2) + 0.47 mH. All 0.33 

oct. smoothing. 

The basic 3 rd order crossover topology is maintained 

in order to give best possible phase response in the 

crossover region. 

As can be seen, the need for the 2 kHz notch filter is 

eliminated by this approach. 

CLIO 

180.0 

Deg


HP-section: 90.0 

180.0 

CLIO 

Not much to say about this part. No problem in 

making the 9500 roll off at 3 kHz. See 

schematics, fig. 4 and response curves fig. 5 and 

6. 

Fig. 4. Crossover schematics for 8535+9500. 

Fig. 5 displays the frequency response from the 

drivers with the new filter and with same polarity a 

dip is seen at crossover frequency. 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


Fig. 5. Red = frequency response with inverted 

polarity, 0.33 oct. smoothing. Green = same polarity, 

0.33 oct. smoothing. Blue = same polarity, no 

smoothing. All measurements performed at tweeter 

height, 1 meter distance. 

I’m quite sure tweeter level will be an issue and the 

2R2 can be changed from 1–2.2 ohms resistance 

without affecting point of crossover. 

CLIO 

180.0 

Deg 

dBSPL 

80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


Fig. 6. Roll-off of both drivers with new filter. 

Graphic presentation of new crossover for bi-wiring: 

Fig. 7. Crossover schematic, layout for bi-wiring. 

Deg 

28

Sonic evaluation of modified 2.5 clone 

The 9500s have the ability to bring forward the best 

qualities in the 8535s and the word that first comes to 

my mind is coherence. To my ears the 8535 has a 

kind of old-fashioned full-range sound, yet in a 

completely other league than the old PHILIPS 9710 

‘full’ranger’ or the like. 

It has its ‘virtues’ in terms of a rather robust 

midrange that is quite demanding on your choice of 

recordings. It is rather merciless on poor recordings 

and inadequate electronics and will probably always 

be so. 

With the new tweeter in place the degree of 

transparency rises considerably and we know how 

much the low end adds to the sense of transparency, 

and the 8535 has that ability, so we are close to 

getting it all from this modest two-way floorstander. 

Quite amazing. The new design appears to give a 

slightly more distant perspective and for sure the 

sibilant, whizzer sound is gone. 

I think that the elimination of the notch filter by 

redesigning the LP section does a great deal to 

enhance transparency. Notch filters can ‘solve’ acute 

problems, but I still have the feeling they can add 

some obscure/subtle phasiness to the region affected. 

Looking at the CSD data from the region where the 

notch filter works, it looks like we have to look over 

a hilltop to spot the start of the transient, meaning 

that despite having an apparent flat frequency 

response it seems as if the energy is slightly delayed 

(page 6, latest v5) in the region affected by the notch 

filter. 

Ideally we want only the forefront of the sound wave 

to hit the ear followed by an immediate decay within 

the first 0.5 milliseconds. 

The 9500s seem to have a slightly recessed high end 

(> 10kHz) compared to the 8513s, despite having a 

very flat frequency response, and I believe this is a 

very common observed phenomenon with most 1” 

soft-domes. 

2.5 clone with ScanSpeak D2905-9500 tweeter. 

29

The Final 2.5 Clone, the “sibilance” problem 

1 st WARNING: 

I have recently (May 2003) acquired my third pair of 

18W8535-00 drivers, and much to my surprise these 

drivers were heavily coated on the rear of the 

membrane. 

These drivers were meant for a three-way 

construction so they perform as expected, but for 

those who buy this new batch of drivers from 

ScanSpeak it appears that they will not perform in 

accordance with all the material that has been 

published until now regarding the 2.5 clone. 

Due to the coating they will have an earlier roll-off 

characteristic and will require modifications to the 

crossover. 

2 nd WARNING 

The tweaks suggested in the following paper deal 

with the D2010-8513 tweeter. 

You will have to dismantle the driver and – 

• remove the ferrofluid 

• damp the pole piece 

• coat the membrane with DAMAR resin 

• if you haven’t coated the dust cap on the 

8535 driver you will have to perform this 

operation also 

• do minor modification to the V6-crossover 

If you feel uncomfortable with finer mechanics 

you may ruin your 8513 tweeters. 

The tweeter is a delicate construction, but with 

proper care you can easily dismantle the 

construction and perform the tweaks. 

The reason for these tweaks is sibilance: 

Definition: 

Sibilance: “Essy”. Exaggerated “s” and “sh” sounds 

in singing, caused by rise in the response around 6– 

10 kHz. 

See: http://www.linkwitzlab.com/images/graphics/sdqulty.gif 

Before proceeding I have to thank Darryl Nixon, 

Australia, for an extensive mail exchange on the 

phenomenon of sibilance and in particular the less 

than appropriate performance of the 8513 tweeter. 

The phenomenon characterised by the word 

“sibilance” has proven more than difficult to deal 

with in the case of the 8513 tweeter. If we stick to the 

definition literally, we should be able to solve the 

problem by adjusting the response in the critical area. 

Various attempts have been tried in order to alter the 

frequency response in the 4–10 kHz region by 

changing the crossover and introduce notch filters, 

etc. But none of these changes gave results worth 

30 

pursuing. The sound from the tweeter still sounded 

awful on a number of especially vocal recordings. 

If you make a search on the web on the word 

“sibilance” you get quite a number of hits, mostly 

aimed at recording engineers on how to avoid 

excessive sibilance by choice of microphones or 

electronics. You can even buy a “de-esser” piece of 

electronics to solve the problem! 

From the work done on the 8513 tweeter, it becomes 

apparent that what we perceive as sibilance is not 

necessarily only derived from excessive response in 

certain areas but also from some intrinsic qualities of 

the tweeter. Actually the response is quite flat. 

I have done numerous comparative tests with the 

CLIO measuring system on various tweeters and 

found no apparent poorer performance of the 8513 

tweeter, so I will not be able to tell you by 

measurements why the 8513 tweeter is inferior as is 

or why the suggested tweaks make it sound so much 

better. 

But I’ll stick my neck out and claim a significant 

improvement in performance for those discerning 

listeners who like vocals, strings and brass 

instruments. 

Most likely the 8513 tweeter holds some obscure IM 

distortion that on poorer recordings makes you hold 

your hands to your ears. 

The tweaks will change the performance to a level 

not far away from the ribbon tweeters that currently 

are my reference for best tweeter performance. 

At the same time you will have to adjust tweeter level 

to produce a frequency response at +/– 1.5 dB from 

400–17,000 Hz. That is with the V6.1 crossover with 

8R2 or 9R0 to the tweeter. 

However, the tweaks will enhance performance from 

whatever crossover you may hold. 

I have recently heard the real ProAc Response 2.5 

speakers and had the impression that the tweeter was 

well balanced to the bass driver but the midrange 

hardness and relatively poor midrange/tweeter 

resolution was much the same as what characterises 

the clone. I had a hard time believing that this tweeter 

would have ~ 5 ohm series resistor to the tweeter. 

With 5 ohm to the tweeter the clone sounds just 

awful. 

I don’t care how many reviewers have praised the 

successful integration of drivers in the Response 2.5 

and apparent midrange smoothness. The speakers had 

a slightly smeared midrange with less than proper 

resolution and image focusing compared to other 

speakers and what can be achieved from the 

described tweaks. I’m also sure that some will say 

“goodbye ProAc sound”, and except for the bass, 

that’s just what it’s all about.

31 

Modification of ScanSpeak D2010/8513 tweeter Release the magnet/voice coil assembly by a 

gentle twist of a screwdriver between magnet and 

Disassembling the 8513 tweeter 

housing. Possibly they will just fall apart. 

Fig.1 

With a fine-toothed saw the back plate is released 

from the driver housing. Saw blade should not cut 

deeper than 2–3 mm all the way round in order not to 

damage part of the back plate going into the housing. 

Cut where the back plate is melted to the housing. 

Fig.2 

Fig.3 

Rubber gasket is removed from magnet with a 

screwdriver. The gasket is not glued and is easily 

removed. Take care not to damage the wires from the 

voice coil. 

Fig.4 

All driver parts. 

Fig.5 

Carefully lift off diaphragm/voice coil from magnet 

gap. 

Fig.6 

Voice coil gap and diaphragm assembly.

Removing ferrofluid 

Fig.7 

Remove all ferrofluid with a piece of paper. 

Carefully wipe off any ferrofluid from the voice coil. 

Adding damping pad to the magnet pole piece 

Fig.8 

Here in DK you can buy 17 x 3 mm self-adhesive felt 

pads that fit exactly to the pole piece. 

Punch or cut an 8 mm hole at the center of the felt 

Fig.9 

Damped pole piece. 

Coating of diaphragm 

32 

One layer of DAMAR coating is applied to the 

diaphragm. 

Use a miniature brush and apply DAMAR coating in 

thin and smooth strokes from edge towards center of 

the dome. 

Fig.10 

Do not apply DAMAR coating to the cone 

suspension! 

Leave the coated dome for 1 hour at room 

temperature and assemble driver. 

pad and press firmly to the pole piece. Coating will be fully dry after approx. 24 hours. 

Assemble driver and tighten back plate to housing 

with silicone glue. Add mild pressure until glue has 

settled, 6 hours.

Listening tests 

The listening sessions were divided in two parts. First 

the tweeter with no ferrofluid + damped pole piece 

was compared to the reference tweeter with no 

modifications. 

The V6-HP section was used before drivers and a 

double switch was attached to the tweeters for quick 

change between the two. SPL measurements were 

performed to ensure same listening level. 

Tweeters were placed aside on a carpet with no front 

panels and the average frequency response looked 

like this: 

100.0 

dBSPL 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

20 100 1k 10k Hz 20k 


red= no ferro fluid blue= with ferro fluid 

Fig.11 

A number of CDs with particularly troublesome 

sibilance were used for the test. 

Listening to a tweeter – solo – above 3.5 kHz at high 

level is no pleasure for sure. Listening to a brass band 

crescendo very clearly reveals poor tweeters and 

improper recordings. 

For comparison, tweeters like the SS9000, 9500 and 

HIQUPHON OWI were included, where response 

levels were corrected via L-pads. 

Ferrofluid 

The removal of the ferrofluid and damping of the 

pole piece did not reveal any significant changes to 

the modified tweeter. Same sound from both tweeters 

with a wide range of musical sources. 

Coating 

When you for the first time are comparing coated vs 

uncoated it is very clear that you now have two quite 

different tweeters! 

The reference un-modified 8513 compared to the 

modified and other tweeters appears “flat” and with 

poor resolution and depth. 

CLIO 

180.0 

Deg 

33 

The coated 8513 immediately appeared to have a 

darker sound compared to the uncoated, which was a 

surprise as frequency response from the two drivers 

was within 1 dB. 

Numerous measurements (SPL, FFT, step response, 

impulse response, cumulative spectral decay, etc. 

have been performed. Tweeter intermods were 

measured with a 10 and 11 kHz input, where 

intermods are at 9, 11, 12 and 19 kHz with all 

intermods down to < 50dB below 90 dB reference 

level. Just as good as any other well-designed 

tweeter. 

In no case was there any significant difference 

between the two tweeters. 

And yet the sound is very different. 

The nature of this “darker” sound was first fully 

unfolded after having installed the two drivers in the 

2.5 clones with the V6-crossover and 8R2 ohm series 

resistor to the tweeter giving a smooth response from 

300–18000 Hz +/– 1.5 dB and < +/– 0.5 dB between 

speakers. 

This “darker” sound now appears in full scale as an 

improvement in resolving power, transparency and a 

more “full-bodied” sound whether being vocal, 

piano, brass, etc. 

And still in mono-mode the coated dome appeared to 

reduce the midrange “hardness” usually associated 

with the 8535 driver. 

Frequency response of the tested speakers: 

100.0 

dBSPL 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

200 1k 10k Hz 20k 


File: 8535+8513-un-coat-modV6-10R-rev.mls red="coated" blue="uncoated" 

Fig.12. Un-smoothed response. 

Red = 8535 + 8513 coated 

Blue = 8535 + 8513 reference (not modified) 

Yes, resolution and depth can be heard in a single 

speaker/mono setup. For the sake of good order the bass drivers were 

swapped and the same tests were repeated with much 

the same results. 

CLIO 

180.0 

Deg

Getting two bass/mid drivers to sound exactly the 

same is not an easy task. You may fine-tune the 

crossovers to make the drivers perform within 1 dB 

and yet they may sound slightly different. 

Thus the need to swap drivers and repeat tests. 

Fig.13. Tweeter test. 

(Gaffa tape covering 9500 rebate) 

The intriguing thing about the speaker with the 

coated dome is that it now sounds slightly darker, yet 

having more presence, which I interpret as a better 

midrange-tweeter integration. 

From the speaker with the uncoated dome, voices 

sound as coming primarily from the 8535 with some 

poorly focused highs added from the tweeter, where 

the speaker with the coated dome seems to “dress” 

the midrange with the proper overtones and presents 

a more natural tonal balance. 

34 

Going from the “uncoated” to the “coated” 

removes a curtain, however trivial this expression 

may be, but it very much describes the transformation 

that has taken place. 

Coating of second tweeter 

Fig.14 

After drying for 1 hour the tweeter was assembled 

and reinstalled in the 2.5 enclosures. 

Frequency response was measured after 1.5 hours: 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


Fig.15. Frequency response, no smoothing. 

Red = newly coated dome 

Blue = 72 hour coated dome 

Very much same performance as seen in Fig.12. 

(colours reversed) 

CLIO 

180.0 

Deg

The 2.5 clone now bear little resemblance to where 

it all started with the 2 kHz bump, notch filters, 

etc. 

To summarise the changes: 

• Notch filter is omitted by adding a resistor to 

the LP section capacitor 

• 47 ohm resistor in parallel with the 1.8 mH 

coil is removed 

• 8535 drivers have had dust caps 3x coated 

with DAMAR resin 

• Ferrofluid has been removed from tweeter 

voice coil gap 

• Damping material has been applied to 

tweeter pole piece 

• Tweeter dome has been given 1 layer 

DAMAR coating 

Regards 

Fig. 16. 2.5 clone crossover, version 6.1. Troels Gravesen 

35 

Listening tests on the 2.5 clones with both 

tweeters coated: 

The speakers fitted with the coated 8513 tweeters 

now hold some of the same qualities associated with 

the 8535+9500 setup. 

And the 8535+8513 holds qualities different from the 

8535+9500 combination. 

The 9500 setup is a very good all-rounder that 

handles almost any choice of music and only rarely 

leaves the upper midrange behind in making the 

“perfect speaker”, that is from a modest two-way 

floor-stander. 

The dust-cap coated 8535 + coated 8513 have a 

slightly more analytical presentation and enhanced 

depth presentation compared to the 8535+9500 setup. 

The midrange is improved even compared to the 

8535+9500 setup. I cannot account for this 

improvement, but it’s significant. 

I can now enjoy almost all my CDs, even the poorer 

vocal recordings. 

I’ll reinstall the 8513 tweeters for good and keep 

these speakers and thank all the cloners who 

commented on the performance and suggested 

changes. 

And thanks to JPO for taking in yet another paper. 

This is the final. 


PS. DAMAR coating of the 8535 dust cap: 

Apply 3 layers of DAMAR coating to the dust cap 

with at least two-hour intervals. 

And don’t apply coating outside the dust cap as it 

changes the frequency response around 3–4 kHz.

Comments to tweeter modifications 

1. 

First of all your tweeter mod is excellent, the 

sibilance has really gone and the sound is much 

smoother than before. 

Zoltan. 

2. 

This is quite a delicate operation! The only thing I 

found that was not in your instructions was that after 

the rubber gasket is removed, it is necessary to tap 

the plastic casing on the side to allow the driver parts 

to fall free (at least it was in my case). It confused me 

for a few minutes until I figured it out. Aside from 

that, everything went well. I did both drivers at the 

same time and was keen to hear the result, so I've 

temporarily attached the back plate to the housing 

with electrical tape - don't worry, it's airtight and I'll 

redo it properly with silicone tomorrow. 

Well, all I can say is that together with the minor 

crossover mods and extra Damar coating on the 8535, 

this makes the most significant improvement since 

your original notch filter. Everything you say in your 

paper is 100 per cent correct - the tweeter coating 

really does transform the speaker. The last traces of 

the original clone's "technicolour" sound are gone, so 

I guess it's not going to please everybody, but 

sibilants now sound totally natural, even if they are 

still a bit more pronounced than in some other 

designs. The important thing is that they don't "ring" 

and they don't irritate. I also agree with your 

description of the treble as "darker", and yet - you're 

right - at the same time there's more presence to the 

sound! I think we've been unfair to this tweeter; it 

had far more potential than we were allowing for. 

There is now obviously far better integration between 

the two drivers. It's very strange, but I have to agree 

with you also that the midrange "hardness" is now 

much reduced - or at least much less obvious, and it's 

possible to hear depth layering where it didn't exist 

before. I have yet to listen to all my "difficult" 

recordings, but the few I have tried all showed a 

marked reduction in "listener fatigue". I can enjoy 

most of them again! I can't say I always find the 

"carbon-fibre" midrange to my taste, but I can now 

appreciate it for what it does. The clone truly does 

now fit the description of a "high-end" speaker. Very 

impressive. 

Darryl. 

3. 

I have been briefly comparing Troel's modified 8513 

tweeter (ferrofliud removed an applied damar coating 

to cone) and it is very nice. I must modify the woofer 

crossover to Troel's suggestions before I make any 

final conclusions but dropped it into the current 

crossover and it sounds more neutral, less sibilant 

when CD tracks have too much energy. The same 

36 

basic sound character is retained but enough treble 

zing is shaved off for those who want this, IMO. At 

this point in time I still prefer the standard 

unmodified tweeter as there is more of that original 

Proac lushness, sweetness and detail, but can be 

sibilant on some tracks, which seems to be the tradeoff. 

Al.M 

4.a 

- modifiserte 8513 i går, pluss at jeg satte inn en 

10ohms motstand i mitt No1. Filter. Har forresten 

bestilt deler til No6. filteret i dag.(gleder meg) 

Resultatet av tweakingen er enorm! Må bare takke! 

b. 

After many more ours of listening to the clones and 

the V6 filter, I have come to what will be MY final 

filter. Sorry, but I was a little to fast to accept the 

filter for the 8535. 

The V6 filter sort of shows the true nature of the 

8535, a hard sound....... 

But with the V1 filter too the 8535, and the latest (in 

the link) to the 8513 + the modifications with the 

tweeter, the sound is the most acceptable ever. I can 

still hear the 2000Hz bump but then mostly when I 

listen to TV. The sound on most recordings now is 

warmer than with the V6 filter. But now I can for the 

first time totally relax when listen to my favourites. 

c. 

Dear cloners 

I really recommend this modification of the 8513 

tweeter. I can promise a sweeter treble. And the 

metallic sound is totally gone! In fact the whole 

speaker can be as fantastic as people said, from 

bottom too the top. I have had big problems 

accepting the clone`s sound until now. This tweak 

together with the v6 filter and I can call this speaker 

superior! I agree with Troels that this is the final 

version! 

d. 

There is said many strong words about the sound of 

the clone, but I cant understand how so many people 

have accepted the sound of the early clones! I can 

imagine Mr. Steward Tyler having a good laugh more 

than once! But now He he he......... 

Regards from Tor Hauge...Norway

37 

The new coated 8535 drivers from ScanSpeak b. LCR notch filter for the 750 Hz bump = 10 mH 

(2 x 4.7 mH, 0.65 ohm) + 10R + 6.8uF. 

As mentioned in my former file on tweeter coating, 

the new 8535 drivers have a coating on the rear of the 

cone. This is a deviation from former 8535 drivers 

and is easily detected on measuring performance. 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


Fig.1. New coated 8535 and V6.1 crossover. 

What can be seen from this graph is a 3-4 dB bump at 

600-900 Hz, and due to an earlier roll-off 

characteristic, a dip at 3 kHz. 

Here’s the response from the old drivers with 

modified tweeter, crossover V6.1: 

100.0 

dBSPL 


90.0 108.0 

80.0 36.0 

70.0 -36.0 

60.0 -108.0 

50.0 -180.0 

200 1k 10k Hz 20k 


File: 1st coat 72 h.mls 

Fig. 2. Old 8535 driver response. Blue and red are 

various measurements during tweeter coating. 

It’s my feeling, that these drivers will be best suited 

with tweeters like ScanSpeak 9300/9500/9700 and a 

target point of crossover at 2-2.5 kHz, possibly 6- 

12/18 dB. 

Furthermore, a notch filter is needed for the 750 Hz 

bump. 

To my knowledge, this change in performance has 

not been announced by ScanSpeak and can only be 

identified by measurements or visual inspection. 

I have tried to tweak the V6.1 crossover to adapt to 

these new drivers: 

LP-section: 

a. 1.8 mH-(7.8uF+4R7)-0.47 mH 

CLIO 

CLIO 

180.0 

Deg 

180.0 

Deg 

HP-section : 

No changes. 

Fig.3. V6.2 

90.0 

dBSPL 


80.0 108.0 

70.0 36.0 

60.0 -36.0 

50.0 -108.0 

40.0 -180.0 

200 1k 10k Hz 20k 


File: V6.2-7.8+4R7.mls 

Fig.4. Frequency response of new crossover. 

LCR components: 

Fig. 5. mid-LCR. 

- And don’t spend a fortune on notch filters unless 

you think this is the speaker of your life! 

This shouldn’t cost you more than 20 US$ in all for 

two. 

CLIO 

180.0 

Deg

Fig. 6. “New” coated 8535 

Fig. 7. “Old” un-coated 8535 

Conclusion 

Listening to the V6.1 crossover with the new drivers 

doesn’t sound that awful. 

Compared to the old drivers, we have a midrange 

with some more presence and for sure we are more 

forgiving to dips (3 kHz) than bumps in the 

frequency response (remember the series filter?). 

With the V6.2 filter, the dip at 3 kHz is slightly 

reduced and you can ad the mid LCR if you think you 

have too much midrange presence. With this notch 

filter in place, the midrange is much like the old 

drivers (and there is not going to be an easy substitute 

for this tweak). 

I don’t have two pairs of 2.5 clones to compare, but I 

would have a hard time pointing out one from the 

other. 

Or did I hear some more background details (talking) 

in the midrange from the new, coated drivers on the 

Jazz at the Pawnshop that I haven’t heard before???? 

13.08.03: NEWS on the “new” drivers from Scan 

Speak: 

Finally there’s some explanation from Scan Speak 

regarding these drivers: 

Alain Letendre, Canada, has received this message 

from Madisound: 

38 

The Scan-Speak 18W/8535-00 has always been 

coated both front and back, but as it is an air dried 

cone, its absorbency may differ. We use the same 

amount of coating glue on each unit so the cone may 

sometimes absorb all the coating glue (i.e. the coating 

is hardly visible), and sometimes the cone is saturated 

after absorbing 80-90% of the glue. The rest of the 

glue will then form a somewhat shiny surface, 

leaving the coating visible. I hope this answers your 

question. 

Best regards, 

Danish Sound Technology A/S 

Carina Sondergaard 

Export Assistant 

From d-s-t here in Denmark I have received this 

message (in Danish): 

Hej Troels. 

De variationer i udseendet, som dine billeder viser er 

ganske normale. Der er ikke lavet tilsigtede 

ændringer på denne enhed siden dens "fødsel". 

18W/8535-00 er og har altid været coated på både 

for- og bagside. Ofte er det dog ikke synligt på 

bagsiden, men der kan opstå skinnende pletter, som 

dit billede viser. 

Membranen er luft-tørret (til forskel fra en kontakttørret 

membran som anvendes på fx 15W). Den 

lufttørrede membran suger/absorbere coate-limen 

(som er vand-fortyndet). 

Hvorfor så forskellene? Som følge af fremstillingsprocessen 

forekommer der variationer i den 

lufttørrede membrans indre struktur, mens vægten er 

let at holde (det er den, der er specificeret med 

tolerancer). Det er lufttørringen, som giver det 

specielle udseende på forsiden. Nogle gange vil 

membranen være lidt mere kompakt end andre gange, 

og det påvirker suge-evnen. Mængden af påført 

coate-lim altid er den samme (vi kontrollerer desuden 

viskositet). Den er doseret til næsten at mætte 

membranen. Derfor vil membranen nogle gange 

absorbere al limen, så den ikke synligt er coated på 

bagsiden (som trænet er det let at se, at enheden på 

dit første billede ER coated på bagsiden. Det ville du 

også kunne se, hvis du havde en u-coated membran). 

Andre gange vil membranen i områder lige nå at 

blive mættet, før al coate-limen er påført. Den 

resterende mængde coate-lim vil derfor lægge sig 

uden på membranen. Jeg håber, det har kastet lidt lys 

over sagen. Mvh. Ulrik Schmidt, udviklings-ingeniør 

This message says much the same thing as the 

message from Madisound. 

So, this is production variations and my only 

comment to this is: 

BEST OF LUCK CLONERS! 

Your will probably not be able to determine what 

type of crossover will be best suited for your 

drivers without measuring equipment.

New project to come: 

“The Point75”: 8535 bass +SEAS W15CY001 di-pole midrange + ribbon tweeter. 

Regards 


40

Notes on the ProAc sound: 

Much has been said on the ProAc sound, and this can 

be found in all the reviews seen in HIFI magazines, 

etc. If we take a look at the frequency response 

curves from a number of ProAc Response designs, 

this is what we see: 

Response 1SC 

Response 2.5 

Response 3.8 

The Danish magazine High Fidelity confirms the 

response curves seen from the ProAc 1S and 1SC. 

Response 1S 

Response 1SE 

Response 3.5 

41 

Response 2S 

The Response 2S is an exception from this profile 

and the Response 3.5 is the worst of them all. 

Worst?? 

Well, first let’s take a look at 10 randomly picked 

designs from the Stereophile files: 

(A few speakers with very peculiar response profiles 

have not been considered)

Totem Acoustic Mani2 KEF RDM 

Dynaudio Confidence C4 

JMlab, Chorus 706 

Joseph RM 33si 

Revel Salon 

Spendor S3-5se 

Vandensteen 2ce 

42

KEF Reference 207 

The speakers chosen here are from small monitors to 

large floorstanders. 

Try to zoom out on our PDF reader and watch the 

two pages simultaneously. 

Few of these nine speakers have some or a slightly 

elevated bass response, but none of these have the 

persistent increase in bass and treble response as seen 

from the ProAc speakers, combined with a generally 

recessed midrange. Even the Response 2.5, where we 

can see the 2 kHz midrange bump following an 800 

Hz bump. 

It is apparent, that the Response series was created 

with the intention of maintaining a specific response 

profile, thus giving the “ProAc” sound to them all, 

where the main differences are bass performance, 

logically derived from the size of the cabinet and bass 

drivers. 

This is in no way a new approach and can be heard 

from a number of other manufacturers, where the 

main differences in “sound”, relates to bass 

extension. 

The Response 2.5 800 Hz bump, by the way, could 

be the explanation for the acceptance of the 2 kHz 

bump in the original design. 

The “sum” of these two bumps may kind of even out 

the overall perceived balance. 

(Actually we can now get both of these bumps with 

the new coated drivers from SS. Leave out (or 

reduce) the series resistor in the LP section, and leave 

out the LCR notch filter for removing the 800 Hz 

bump + reduce tweeter series resistor to 5 ohm! 

How about that? Finally we can recreate the original 

ProAc Response 2.5 sound/profile with all the 

bumps). 

In the history of HIFI, response curves displaying 

excessive bass and treble at the expense of a recessed 

midrange, was the trademark of the so called “West 

Coast” sound. Lots of bass and lots of treble. 

Excellent for “Surfin’ USA” by The Beach Boys. 

I remember JBL having a 14” bass driver (LE14) 

married to a small paper cone tweeter. This was a 

“tizz and boom” speaker! 

If you have to make a living of producing 

loudspeakers, you have to catch the attention of your 

43 

audience, and the easiest way to do this, is pushing 

the “loudness” button = “west-coast-sound”. 

“Cheap-trick-low-fi”, that’s what it is. 

Thus the need to re-evaluate the crossover design if 

you want to listen to acoustic instruments and voices 

and have a more natural presentation of an acoustic 

event. 

The ProAc Response designs are nowhere near the 

old “tizz-and boom”/”west-coast-sound”/”boom and 

tweet” sound, but displays a specific profile, aimed at 

creating an “engaging” sound. The objective of 

neutrality appears to be somewhat compromised. 

Quote, Martin Colloms: 

Subjective effects of first-order errors 

“Slight errors in channel balance, either in specific 

frequency ranges or in overall level, can subtly 

disturb one's opinion of the sharpness of stereo focus. 

Statistically well-controlled testing has not only 

confirmed the audibility of absolute phase/polarity 

but also that of level differences as little as 0.2dB. 

These differences may be of octave or several-octave 

bandwidth, with a sensitivity of a similar magnitude. 

The subjective responses to variations in 

amplitude/frequency response are pretty well 

documented; the careful reviewer bears these 

constantly in mind. For example, less than 0.5dB— 

5%—of treble lift in the 3-10kHz range can give rise 

to a mildly increased sense of immediacy, 

transparency, and liveliness without necessarily being 

directly obvious as treble lift. A similar degree of loss 

in the 150Hz-400Hz range can make a vocalist 

appear lightweight and lacking in power in the 

fundamental range, lending a crisper quality to the 

sound. This might be preferred on one recording but 

disliked on another”. 

With the variation in specification of drivers and 

crossover components + cabinet construction and 

damping, not to mention the front-end consisting of 

amps and players, it’s no wonder we get different 

reports on sonic performance of the 2.5 clone. 

It’s my feeling, that if you choose to target the 

original response profile, you’re in for some serious 

tweaking on amps, cables, CD players, etc., to get it 

right. 

If you’re in for the more British school of 

loudspeakers, represented by names like Rogers, 

Harbeth, KEF, Spendor, etc., and target a more flat 

response profile, you will have a speaker, that will 

tolerate a larger range of amplifiers and CD players. 

And to my ears be more “high-fidelity” compared to 

the more immediately appealing ProAc sound. 

On the various schools of speaker designs, please 

read: http://www.aloha-audio.com/library/speakerdesign1.html

The 2.5 clone papers - CCRMA

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