Electro-Voice 7600 - Calculating Power Losses with 8 Ohm Loads; Calculating Power Losses with 4 Ohm Loads; Damping Factor

Operating and Servicing Instructions for the Electro-Voice 7600 Power Amplifier
SOURCE
AMPLIFIER'S INPUTS
AUX OUTPUTS
BALANCED
SOURCE
r HI (+)
XLR BARRIER STRIP
2 ( ♦ )
3 (-)
1 cun
“] 1 11
y lo (-) T ur
jr V
- - ?--
NC
HI
LO
BAL
OUTPUT
BALANCED
SOURCE
W/600 OHM
TERMIN ATION
HI (+)
1' LO h/
NC
XLR BARRIER STRIP
(+)
(-)
END
RESISTOR
|—(6001—[
UNBALANCED
SOURCE
_ HOT
3—f
-d
XLR BARRIER STRIP
2 (+)
3 H
, 1 6NO --
SINGLE-ENDED AUX OUTPUT
r— HOT
COM
rh
UNBALANCED
SOURCE
m
HOT
COM
NC
XLR BARRIER STRIP
2 (+)
3 H
SNO ,-
NC
HOT
COM
KEEP
CABLE
RUNS
UNDER
6 ft
OR 2 id
Figure 3 Typical Input Connections
AMPLIFIER'S OUTPUTS LOUDSPEAKER LOADS
Figure 4 Typical Output Connections
meter) of the 2-wire cable selected
from Table I by the length of the
cable in feet (or meters). For ex¬
ample, suppose an installer uses
160 feet of 10 GA 2-wire cable with
an 8 Q speaker system. The total
power loss in the cable is:
Total Power Loss in cable
= 0.1013 watts/foot x 160 feet
= 16.2 watts
Does this mean that whenever the
amplifier produces 400 watts of
output power, 383.8 watts (400
watts minus 16.2 watts) will be
delivered to the 8 ohm load? NO!
The actual load impedance is 8
ohms plus the resistance of the
cable (0.00204 ohms/foot times 160
feet) for a total load impedance of
8.3264 ohms. At the 8 fl rated out¬
put power, the output voltage is
56.57 V rms. Therefore, the amp¬
lifier produces 384.3 watts with
this load instead of 400 watts. This
was calculated by squaring the volt¬
age and dividing by the load
impedance (56.57 2 divided by
8.3264 ohms). As a result, the
actual power delivered to the load
is 368.1 watts (384.3 watts minus
16.2 watts).
Had 18 GA wire been used in the
above example, the loss in the cable
would have been 100.8 watts. This
example illustrates the importance
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 48.6 watts of
power while the 18 GA wire would
waste 302.5 watts - more than half
of the amplifier’s 4 ohm power rat¬
ing.
3.4.1 Calculating Power
Losses with 8 ohm
Loads
To calculate the total
power loss in the speaker cable,
multiply the power loss per foot (or
3.5 Damping Factor
The higher the damping
factor rating of an amplifier, the
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