Constant Voltage Systems

The situation is not quite so upsetting in the series

connection where the 8-ohm speaker accepts only

one-half the power of the 16-ohm speaker. The power

efficiency/power input ratio now becomes

Taking only one-half the input power of the 16-ohm

speaker, the 8-ohm speaker is producing 2 1/2 times as

much acoustic power.

CONSTANT VOLTAGE SYSTEMS

With the constant-voltage distribution system, you

can distribute audio power without having to match

impedances or be too concerned about the effect of

changes or additions on one part of the distribution

system.

Assuming that the line voltage from the amplifier is

Figure 4-19.-Network mesh systems may be employed with the

constant, you can make easy, on-the-spot level

constant-voltage system where speaker group may be

adjustments of an individual speaker to suit the needs of

considered single load.

the particular area served by that speaker on the line. In

addition, you conserve audio power.

In a 70.7-volt system, power delivered is

There are disadvantages to the system, too. Though

wire runs are economical, each speaker or group of

speakers requires its own line tie-in transformer and the

main amplifier requires one master transformer.

In a matched-impedance system, the impedance

must be calculated on each speaker group. Various

speaker configurations will be necessary to get a usable

impedance for any one branch. In a constant-voltage

Problem: You have a transformer whose 8-ohm

system, such as the 70.7-volt system (fig. 4-19), these

secondary is connected to an 8-ohm speaker. What

values are precalculated by the manufacturer of the

should be the impedance of the primary to deliver 50

amplifiers and transformer. The line-matching

watts to the speaker from a 70.7-volt line?

transformer has taps on the primary, marked in units of

Solution:

power (watts), that will be delivered from the 70.7-volt

line when the secondary is connected to a 4-, 8-, or

16-ohm speaker (fig. 4-19).

The precalculated values for the transformer will

If you wanted to draw 5 watts from the 70.7-volt

hold if the input voltage of the transformer is maintained

line, the impedance of the transformer primary must be

at 70.7 volts. The amplifier gain control should be set at

the point where the loaded amplifier delivers 70.7 volts

RMS across the line at maximum load.

Though you need not do the calculating for

impedance, it is easy to do. By formula, power P across

an impedance equals the square of the voltage divided

The individual constant-voltage transformer at each

by the impedance; that is

speaker makes it possible to quickly adjust the power

into the speaker for a given sound coverage. Also, where

there is a mix of cone speakers and horn speakers, you

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