Tenma 72-6947 - Measuring 25 V;70 V Distributed Speaker Systems

-5-
(10 W)
(50 W)
(200W)
AUDIO IMPEDANCE TESTER
CAT.III 100V
OFF
72-6947
20W
200W
COM
TEST ON / OFF
2000W
HOLD
-+
DATA HOLD
Measuring 25V/70V Distributed Speaker Systems
5. Large distributed systems typically utilize 25.2V or 70.7V transformers 
(50V and 100V in Europe), to greatly ease the connection of multiple 
speakers and facilitate long cable runs. These speakers are connected in 
parallel, as shown, with total wattage ratings added to calculate the overall 
rating of the system. Connecting this meter to a speaker arrangement 
such as this will provide the overall impedance of the system.
Using the formula shown below you can calculate the wattage.
Simply put, when connected to a distributed system, take the voltage 
of the system (normally 70.7V or 25.2V), squared, divided by the 
impedance displayed on the meter. Your answer will be the total 
system wattage. This total wattage must not exceed the wattage 
output rating of the amplifier, or damage may occur.
E
— = P
Z
E = Voltage Z = Impedance P = Wattage
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