Rated Power vs. Measured Power

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The following chart lists the power ratings and actual measured power of several amplifiers. The models marked with (A) are automotive amplifiers and were measured with a supply of 14.0 volts and a load impedance of 4 ohms. The other amplifiers were tested at 120 volts with an 8 ohm load except for the BFI and the two Peaveys whose ratings are given at 4 ohms so that's where I measured them. I was careful to maintain 14 volts when testing the auto amps (on an adjustable 100 amp supply) but I made no effort whatsoever to maintain the voltage at the wall receptacle on the others. My house is wired with 12 gauge wire and testing was done about 50 feet from the Service Entrance and Load Center. The Rated Power column indicates advertised power per channel. Likewise with the measured Clipping Power (it is also per channel.) Notice that most of the automotive amplifiers fared very poorly in this test.

You may want to consider that the only real significance to amplifier power is how many decibels of sound pressure it is capable of driving a speaker. Since speaker efficiencies are often specified as decibels with one watt of input a convenient and more useful way of comparing amplifier output would be to reference their decibel output to one watt. This reference system is called dBW. It gives a much more accurate representation of amplifier output than the watt rating system because it considers the part we care about (decibels.) I have included this rating with my measurements.


Manufacturer Model Rated Power Decibels ref 1W Clipping Power Dynamic Headroom
Akai AA-V301 60 watts 18 dBW 113 watts 2.7 dB
Akai AV-U8 28 watts (1) 14 dBW 50 watts (1) 2.5 dB
BFI 1240 200 watts 23 dBW 360 watts 2.6 dB
Bogen C-35 35 watts 15 dBW 40 watts 0.6 dB
Fisher RS-911 100 watts 20 dBW 170 watts 2.3 dB
Frazier F-106C 100 watts 20 dBW 100 watts 0.0dB
Heathkit W5M 25 watts 14 dBW 25 watts 0.0 dB
Hitachi HTA-25F 25 watts 14 dBW 45 watts 2.6 dB
Jensen (A) A-30 15 watts 12 dBW 16 watts 0.3 dB
LXI 9295 100 watts 20 dBW 160 watts 2.0 dB
Majestic (A) MA300 150 watts 22 dBW 100 watts -1.8 dB
Marantz 2220B 20 watts 13 dBW 36 watts 2.6 dB
Marantz 1060 30 watts 15 dBW 50 watts 2.2 dB
Marantz 240 120 watts 21 dBW 150 watts 1.0 dB
Masco MA25PN 25 watts 14 dBW 25 watts 0.0 dB
Optonica SA-5407 70 watts 18 dBW 128 watts 2.6 dB
Peavey XR-600 200 watts 23 dBW 240 watts 0.8 dB
Peavey CS-400 200 watts 23 dBW 240 watts 0.8 dB
Philmore PA-230 30 watts 15 dBW 10 watts -4.8 dB
Pioneer (A) GM-120 60 watts 18 dBW 42 watts -1.5 dB
Precision Electronics 10PA 10 watts 10 dBW 8 watts -1.0 dB
Precision Electronics ST100E 100 watts 20 dBW 100 watts 0.0 dB
Precision Power (A) APA-100 50 watts 17 dBW 64 watts 1.1dB
Profile (A) AEQ-100 25 watts 14 dBW 16 watts -1.9 dB
Profile (A) A400 200 watts 23 dBW 56 watts -5.5 dB
Pyramid (A) PB448 200 watts 23 dBW 64 watts -4.9 dB
Rauland 4050 A 40 watts 16 dBW 40 watts 0.0dB
Realistic STA-110 22 watts 13 dBW 40 watts 2.6 dB
Realistic MPA-50 50 watts 17dBW 60 watts 0.8 dB
Realistic STA-800 35 watts 15 dBW 60 watts 2.3 dB
Sanyo Plus A-35 50 watts 17 dBW 85 watts 2.3 dB
Smart TA-242 120 watts 21 dBW 170 watts 1.5 dB
Webster 95B25 25 watts 14 dBW 25 watts 0.0 dB
Webster TP45 45 watts (2) 17 dBW 45 watts 0.0 dB


(1) The Akai AV-U8 Amplifier is a European model designed for line operation at 100 volts with an intended output of 20 watts per channel. Operation in the United States at 120 volts is possible. The 20 percent increase in supply voltage results in an approximate 40 percent increase in output power. I have operated the amplifier for some time under these conditions with no problems but the heat sinks were not designed to deal with the extra power for extended periods of time. Power above 20 watts should be considered as Dynamic Headroom power.

(2) The Webster TP45 PA amplifier is rated 30 watts RMS, 45 watts Music Power.


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