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Electronics-World-1959-05 Acoustic Research AR -3 O University Ssromberg- Carlson MSS -491 Some special speaker setups that represent the various manufacturers' answers to the best way to hear stereo. ?Carlson Model 1 S -CFW 'en Model DS100 Fisher "Ambassador 11" GOOD many loudspeaker manufacturers have put in a lot of work A finding out just what "makes stereo." They may have come up with different conclusions (which adds to the confusion), but one can credit them with honest effort, both for their research and in making available products consistent with their "findings." We discussed the reasons for these differences in Part 1 of this article - so now let us consider some other aspects. Some manufacturers have been quite "purist" and produced only systems that give stereo in its best or "final" form; if you want stereo, according to them, don't settle for any half measures. Others have catered to people who have monophonic hi -fi and want to convert to stereo by adding a channel (as a first step, at least) or for people with practical limitations: no room for the "conventional" set -up or an awkward shaped listening area. "Add-On Units" Early in the field of the "add -on" market was Electro -Voice with the "Stereon." This is a versatile unit intended to take the mid -range and highs of the second channel (left or right) while the bass of both channels is fed to the bass unit of the original system. A filter is provided to do this, as shown in Fig. 7. University has also introduced three add -on "Stereofiex" units. 42 However, with some University woofers, the dual voice -coil makes the filter for diverting bass from the second channel to the original woofer unnecessary. One voice -coil of the "common" woofer is fed from each amplifier output by a relatively simple connection (Fig. 5) . This add -on approach is not favored by other manufacturers, however. They feel that in most instances the add -on unit will eventually be abandoned in favor of a more ideal system. While this is probably true, there may also be some places where "one large, one small" fit so well they will remain. It can give quite good stereo presentation, although admittedly, where circum- Fig. 5. This is the connection possible with the University "Stereoflex- as employed along with double -wound woofer. MID -RAP GE 9 GM UNITS tt -AOYER CROSSI OOFER TERMINALS 6611 ORIGINAL LOUDSPEAKER SYSTEM E TRA I AMPLIFIER stances allow, better arrangements are possible. Another approach that can be considered as an "add -on" one is the Stephens " Stereodot," although this is really a system approach. However, it can be added on to an existing hi -fi system by including two "Stereodot" side speakers (which are very small) and the control unit. It is an extremely versatile system because the small "Stereodot" units can be mounted almost anywhere. It also provides for "center fill" by feeding a mixture of middle and high frequencies to the original wide -range loudspeaker, as well as using it for the bass of both channels (Fig. 8). A very versatile system in this category is one used in several Columbia consoles. This is not so much an add -on deal as it is a unit with which you can do many things. Primarily designed as the master unit of the "Isophonic" system (mentioned in Part 1) when used this way the console speaker handles common bass only, with the left and right mid -range and highs (above 250 cps) being fed to the small "Isophonic" units. The difference between this arrangement and the Stephens system was explained in the previous article. Additionally, a jack -plug arrangement permits the same console to be used with another full -range speaker system, feeding one channel (left or right) ELECTRONICS WORLD

I1 REFLECTING DOORS to the external speaker and one to the internal speaker. The possible combinations are shown in Fig. 9. Of course, many other systems can be built on the add -on principle, merely by buying another unit similar to the one you already have and installing the additional electronics somewhere. It would be impossible to describe here the variety of ways in which this can be done. But we should warn against buying a second very large multi -unit system. Not only will the distaff side probably object to your hobby occupying too much of the living room, you will not get the best stereo -in fact you may not get stereo, period! Speakers for stereo must give an impression of point- source radiation, if you plan to use two alike, spaced apart in the conventional manner. If you already have one of these large "superdupers," I have two suggestions: either buy a complete separate stereo system and keep the original for mono only or else buy one of the add -on systems, utilizing your single system for part of the stereo -but not for just one channel. "Unitized" Approach So much for the add -on approach. Next we turn to the "unitized" approach- putting a complete stereo loudspeaker system for both channels into one cabinet. Several people have tn REFLECTING DOORS 1 l 1G1 Fig. 6. Three basic constructions used for unitized cabinets. material, they each can project sound that appears wider than the piece of furniture from which it actually comes. Choice should be governed by the acoustics of the room in which you will install it, bearing in mind that too little reflection can sound "dead" while too much results in confusion. The direct radiator, without reflectors, will perform best in recreation -type rooms while a type provided with doors that bounce sound off the wall deliberately are better in a room that is "well upholstered." Quite another type of single- piece -offurniture entry is the Ranger- Lansing "Paragon" (Fig. 10) and its junior version, the "Metregon." These crossfire the sound into a curved reflecting surface, the object of which is to even out the mean path distance from each unit to the listener in various parts of the room, thus spreading the area of acceptable stereo. The reflector alters the apparent position of the two units according to where you sit, so as to optimize stereo in different positions. This optimizing of the presentation in different positions in the room should not be confused with providing "center fill." Actually the latter is best done by using better microphone techniques in recording. Where this has not been done, a center loudspeaker may help to a limited extent. At the same time, this hole -in- the -middle effect can be more noticeable with some types of loudspeaker than others. The horn type produces an effectively large area sound source and is more prone to exhibit the effect just mentioned than some other types. For this reason, Paul Klipsch, who advocates horn -type loudspeakers at opposite ends of the longer wall of a room (Fig. 11) developed his "Heresy" for the middle position, together with a simple phantom circuit for connecting it to virtually any pair of stereo amplifiers, so it receives a matrixed signal. This is also the philosophy behind the remixing of middle for the center speaker in the "Stereodot" system. But optimizing stereo, so its effect can be heard in positions other than center is another thing. This is what various approaches try to do in different ways. The deviant sources of Fig. 6 do it by changing the type of sound distribution from each unit received in different parts of the room. The cross -fire- with -reflector system on Ranger -Lansing does it by shifting the apparent loudspeaker unit positions according to where you sit. The "Isophonic" system of Columbia utilizes the radiation pattern in yet another way, to modify receiver intensity from each unit according to where you sit. Each of these three methods works, but produces different results. Which is best? While, as we have said, this may vary with individual rooms in which they are tried, the difference is also subject to individual hearing faculties and experience and although I may not be very helpful in saying this, the only way to know which suits you best is to SPECIAL CONTROL NETWORK MID -RANGE ANO MGM ONLY Fig. 7. Connections and network arrangement for he Electro- Voice "Stereon" "add-on" unit is shown in this illustration. done this -in slightly different ways. Most of these are essentially an approach for the small -to- medium sized room. Some angle the speakers outward for direct radiation (Fig. 6A) ; some point them out opposite ends with movable reflectors (Fig. 6B) ; and at least one ( Unirersity "Trimensional") does this with the reflectors in front of the units (Fig. 6C) so as to further utilize wall reflections. Some of them use common and some separate woofers. The University version uses a common woofer with twin voice -coils and utilizes radiation between the cabinet back and room wall to improve the low end. Each of these arrangements uses outward- facing units for the mid -range and high frequencies. Used on stereo May. 1959 Fig. 8. Block diagram and connections that are utilized in the Stephens' "Stereodot" loudspeaker arrangement. See text. Table 1. Composite stereo assemblies with speakers for two channels in one unit. MAKER MODEL Ampex A -423 Separate Bozak B -304 Separate Fisher Futura II Separate Fisher Ambassador II Separate Frazier Stereorama I Separate Frazier Frazier Hartley Jensen DS -100 Lansing, J.B. Paragon Lansing, J.B. Metregon Tannoy University Stereorama II Separate Stereomaster Separate 217 -Duo Separate2 Separate Separate Separate Lanseer Separate Trimensional Single SINGLE OR SEPARATE SOUND DIRECTIVITY WOOFERS VARIABLE BY FIXED Divergent Hinged Doorst Divergen- t, 30' Divergent, 30 Divergent, 30 Divergent, 40 Swivel Mount Cross -fired Cross -fired Divergent, 12° Hinged Doors3 - Notes: 1. Hinged behind end -faced units to reflect sound forward. 2. Hartley 217 extended -range units carry whole range in each channel. 3. Hinged in front of end -faced units to further reflect sound against room walls. SOUND RE- FLECTOR USED? Yes Curved Curved Yes 43

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