Electro-Voice 7300A Owner's Operation And Service Instructions page 5

Operating and Service Instructions for the Electro-Voice 7300A Power Amplifier
This example illustrates the im¬
portance of using the proper wire
size.
3.4.2 Calculating Power
Losses with 4 ohm
Loads
To calculate the losses
when using a 4 ohm speaker sys¬
tem, multiply the loss at 8 ohms
by 3, In the above example, the 10
GA wire would consume 24.3
watts of power while the 18 GA
wire would waste 155.7 watts -
more than half of the amplifier's 4
ohm power rating.
3.5 Damping Factor
The higher the damping
factor rating of an amplifier, the
greater the ability of the amplifier
to control unwanted speaker cone
movements. When a signal drives
a woofer, current flowing through
the voice coil creates a magnetic
field. This field interacts with the
permanent magnetic field in the
gap and forces the combination
cone and voice coil assembly to
move outward. When the signal is
removed, the assembly moves in¬
ward but its momentum causes it
to overshoot its resting point. This
overshoot will dampen itself out
eventually but the unwanted mov¬
ements can add considerable dis¬
tortion products to the sound.
In the process of moving inward
through the magnetic field, the
voice coil assembly generates a
current of opposite polarity to the
original signal. This current
induces a voltage or "back EMF"
which travels through the speaker
wire to the eimplifier's output.
The lower the amplifier's output
impedance, the faster the over¬
shoot of the voice coil will dampen
out. The output impedance of an
amplifier can be calculated by
dividing the rated output impe¬
dance, typically 8 ohms, by the
damping factor. The 7300A has a
damping factor rating of 200
which corresponds to an output
Electro-Voice
®
a Mark IV Company
3