Originally Posted by Ricci
There always seems to be an argument over just how long an amplifier should be able to maintain output, ratings and some other things. Some of us would prefer that an amp could sit there and do a sine wave for an hour without cooking itself. Others feel that 30ms is enough duration. Most are probably somewhere in between. Do you use a real unregulated AC line? Lately it seems that manufacturer's are siding with marketing and the bigger the # you can claim the better, so we are getting burst ratings of 4000w (EP4000), 6000w, 18000w etc...A lot of people suggest that you "test the amp in the real world" and that's what I'd like to discuss.
There will be many different answers, since "real world" is subjective. The whole "music power" thing has led to endless debates since "music" means different things to everyone, and as a matter of fact amp manufacturers don't actually rate "music power" based on music.
In my opinion RMS power is the only meaningful number because it's the only one which everybody tests in the same way. But of course, let's go into the whole "music power" thing.
A number of people mentioned the 1/8 rating, that 1/8 peak power represents average energy in a music piece. Okay let's take that as base and rate according to that. But wait... With the whole "loudness war" trend still going on, the average power of music is increasing. So what do we rate with then? We invent a "burst power" which can be everywhere from one second to one cycle of a 1kHz sinewave. And thus chaos ensues.
Now, let me explain the pro audio world a bit. We won't talk about infrasonics since bass in pro audio usually stops at 50Hz. I was actually arguing with a DJ a few weeks ago, he insisted that you can't hear lower than 45Hz, that's why the highpass filters are set for 50Hz. I should have directed him to the IB Cult...
Okay, so we don't need high levels of very low frequencies in pro audio. However, things like impedance mismatch and the use of limiters (or even no limiters at all, hard clipping), are common in pro audio. So take a 2kW amp which is rated with the 1/8 ratio mentioned above. If a limiter is used to squeeze more power from the amp, while driving a 4-ohm load on one channel and a 2-ohm load on the other will it still perform as advertised or will it go up in smoke? Well, i've seen plenty of the latter.
But this forum is about home theater and tons of sustained LFE. In movie soundtracks, even if the long-term average level (let's say average of 10 minutes) is often lower than the 1/8 ratio, there are sustained bass effects 10 seconds in length and even more. So will the 2kW amp really deliver 2kW for 10 seconds when it has been rated for bursts of 100 milliseconds? Again, debatable. Thus i still feel that the RMS rating is the way to go.
But to satisfy the "music power" crowd i'd test in the following way besides RMS: The most demanding instrument in live music is the kick, correct? Well, let's consider a typical kick drum sample, with a sharp attack at 0dB and the bass part that follows the attack at -12dB. This fits into the 1/8 power rule. So let's make this kick drum say 300msec long. Now, kick the kick
and see how far you can go without clipping the attack, and there you got "music power".
That'd be my opinion, anyone can comment or criticize.