Axiom Home Page Forums General Discussion Technical Questions Amps and Power, for Micah

No, Micah; an amp rated at 1000 watts per channel has to output that full 1000 watts continuously for at least five minutes with the number of channels required(at least two)being simultaneously driven. That's the test required by FTC regulations for all amps sold in the U.S.(and effectively, Canada as well). The 1/8th power test, which I've mentioned here several times in the past few years, is a different UL(Underwriters Laboratory)test for fire safety, which the unit has to survive without overheating. 1/8th isn't just something picked at random, it's been found to be a rough average of the power that's used in playing a typical music CD. That is, sometimes less than 1% of full power is used during the playing, at other times 100% might have to used, but the average over the 60-80 minutes would be about 12% of the full power rating.

This 1/8th power number is also typically the number used(unless specific language such as "full power" is used)when the manufacturer quotes a power consumption figure and puts it on the back of the unit. This misleads those who think it's consumption(including the dummies on the first page of the AVS thread Fred linked)at full power into thinking that the manufacturer is lying, since the consumption number shown is less than the full power output claim, and obviously amps work at less than 100% efficiency. As I've described before, the idea is that at 1/8th power class AB amplifiers are about 20% efficient(class D is somewhat higher), so a "7X100 watt" unit running at 1/8th of full power would be putting out about 90 watts total and would require about 450 watts input to do that. So 450 watts power consumption gets put on the back of the unit and the uninformed laugh/scream because obviously 700 total watts can't be output with 450 watts input when efficiency is well under 100%.

Fred, I got so disgusted with the silly talk on the first page of the AVS thread that I stopped reading. However, if you say that someone from Peavey later brings in factual information, I'll read the rest. Fortunately I read very quickly; I took one of them speed reading courses and was able to read War and Peace in 50 minutes(it had to do with Russia).

One point that I can add at this time is that the term "RMS" power or watts shouldn't be used, because there is no such thing(despite frequent use, sometimes even by manufacturers). Voltage continuously varies from about +170 to -170(in North America)and a special type of average called root mean square is used(comes out 120 volts)to show the effective overall voltage. This is used when it meets something(like a speaker voice coil) that has a resistance and results in power being used. A watt itself is a fixed amount of power and doesn't vary, so no RMS or other average is needed to express it.