A Guide to Quality Installed Sound Systems. - Jands

technical
references
Calculating Speaker Impedance
Where multiple speakers are connected it is important to maintain
the correct impedance so as not to damage the amplifier. Most
multimeters only measure resistance - impedance is different.
Resistance is the measurement of DC current and the resistance to
its flow, impedance is the measure of the resistance to flow of AC
current, which varies with frequency. Typically an 8 ohm nominal
impedance cone speaker has a DC resistance of 6 ohm. To measure
impedance a dedicated meter is required, these use a 1k frequency
the result of which should be cross referenced with the speaker’s
impedance chart to see what value should be expected.
Speaker Wiring
Configurations
Guide to IP Ratings
IP ratings are used to designate an object‘s resistance to environmental
ingress. For example, our IP65 equipment enclosures are totally protected
against dust ingress and low pressure water jets from all directions.
General Guide to IP Ratings
The table below shows general descriptions for IP ratings. They are a guide
only, for detailed information consult the relevant Australian Standard.
First Digit
Solid Object Ingress
Second Digit
Liquid Ingress
0 No protection No protection
1
Protection against solid objects
over 50mm eg. hands
Protection against vertically
falling drops of water
Wiring Speakers In Series
Speakers in series double the nominal speaker impedance, ie. two 8Ω
speakers become 16Ω. Typically used in band PA speaker boxes, nightclub
speaker systems, DJ systems and car audio systems.
Wiring Speakers In Parallel
Speakers in parallel halve the nominal speaker impedance, ie. two 8Ω
speakers become 4Ω. Typically used in band PA speaker boxes, nightclub
speaker systems, DJ’s systems and car audio systems.
Wiring Speakers In Series Parallel
Speakers wired in series parallel are used to maintain the same impedance
as a single driver. ie four 8Ω speakers wired in this configuration represents
an 8Ω load to the amplifier. This arrangement substantially increases the
total SPL of the system compared to one single driver.
Wiring Speakers In Parallel for 100V Line
Where several speakers are to be used at one time, on one circuit, it becomes
necessary to use speakers fitted with line-matching transformers. This is to
overcome the effects of connecting speakers in parallel and cable losses. The
amplifier system generally has an output voltage of 100 volts. This is then
applied to the speaker transformers. In this configuration the total wattage
load on the amplifier is derived from adding all the line transformer primary
tap ratings together. For example, 70 one watt speakers will have a total
speaker load of 70 watts. Or alternatively, it is conceivable to connect 100
one watt speakers to a 100 watt, 100 volt line amplifier.
2
Protected against solid objects
over 12mm eg. fingers
Protected against direct sprays of
water up to 15° from vertical
3
4
5
6
7
8
Protected against solid objects
over 2.5mm eg. tools
Protected against solid objects
over 1mm eg. wires, tools
Protected against dust limited
penetration permitted (no harmful
deposits)
Totally protected against dust.
ie sealed
Protected against sprays up to 60°
from vertical
Protected against water sprayed
from all directions
Limited penetration permitted
Protected against low pressure
jets of water from all directions
Limited penetration permitted
Protected against strong jet
of water. Limited penetration
permitted eg. marine environments
Protected against effects of
immersion between 150mm
and 1m
Protected against effects of
continuous submersion at a
specified depth
Jands Technical References