eggontoast said:
davedotco said:
RMS ratings tend to be considered the benchmark, but sadly they are of little use, they can be so easily manipulated. in fact very little of what the manufacturer gives you is any use at all.
The most useful rating is probably 'peak power', ie the output that an amplifier can sustain without clipping. Sounds simple but specifying the load conditions and the time period that the peak power can be sustained is difficult. Ideally you want an amplifier that can sustain it's peak power for the duration of that peak, then do it again a few fractions of a second later, very difficult to specify and even harder to measure.
Not sure what rms figures you have seen which are manipulated. If the specifications give an rms figure for 8ohms, 4ohms and 2ohms (which they usually do) this gives a good indication of power, especially if the power doubles as the impedance halves. Very rarely do you see manipulated figures from Hi-Fi manufacturers;
in most cases the amplifiers exceed their specification when tested.
Which is itself a form of manipulation....! Everyone knows that 'Naim watts' are more powerfull than 'ordinary watts'.
Mostly the figures are manipulated by not being complete. Many mainstream amplifiers are now quoting power into 6 ohms, not 8 ohms as was once considered the norm. They may well deliver the rated power into an 8 (or6) ohm resistor, but a real world speaker like a B&W where the impedance drops to 3.2 ohms?
Similarly, how long can they maintain this power? Driving heavily compressed music into a difficult low impedance speaker is quite difficult, many mainstream amplifiers will not cope well under these conditions even though the actual continuous power delivered by the amplifier is way below it's specified continuous power ratings. The power ratings are of little use in these examples.
How can manufacturers get away with this? Simple, in my first post I showed how little continuous power is required by most systems most of the time, as long as the amplifier is only called upon to produce such power, remember 1 watt into an average speaker may produce 87dB spl, already very loud, they will be absolutely fine.
But in more demanding system? Low sensitivity speakers, low impedence speakers, heavily compressed music, a bit of bass boost, higher than average playback levels and pretty soon the amplifier that was doing so well in the previous paragraph is now hideously out of it's depth.
The important thing for anyone coming to this hobby for the first time is to understand how few watts are needed most of the time and how many are required the moment we ask a system to 'do a little more'.