Originally Posted by commsysman
The fundamental problem with HT receivers is very simple; they skimp on the power supply.
It is only skimping if there isn't enough power to run the equipment as actually used.
Most HT receivers (Cambridge excepted) have power supplies that are only 400-500 watts TOTAL. They barely have enough juice to run 2 channels well, and 5 or 7 channels is a joke. power drops off dramatically, and the amplifiers are usually lousy designs too.
You are no doubt talking about bench testing.
Bench testing generally involves pure sine waves and resistive loads. This is per industry standards (DIN, JIS) and sometimes legal due to requirements (The USA Federal Trade Commission - FTC)
Real world usage involves loudspeakers and music, dramatic sounds, and speech.
Music has far less energy in it than a pure tone of the same amplitude.
The difference is no less than 3, and can be 10 or more. IOW music with instantaneous peaks of 100 watts can contain the same average power as a pure sine wave of from 5 to 30 watts.
For example here is a musical selection I picked randomly:
Here are its statistics:
Lots of numbers. The ones to watch are "peak amplitude" (should stay the same +/- 0.5 dB and "average rms power" which is the energy in the signal as compared to direct current with the same amplitude.
Here is a pure sine wave:
Here are its statistics:
Note that I approximated "peak amplitude" within +/- 0.5 dB. Compare "average rms power" here for a sine wave to the same number for my music sample.
Notice that there is an approximate 10 dB or more difference in the average rms power contained in the sine wave as there is in the music. The sine wave has about 10 times as much average power as music with about the same peak amplitude.
Speakers are a load whose impedance varies with frequency and is often higher than its rating which is usually taken at a minimum or near-minimum.
This is especially true of the Q900s whose impedance curve looks like this:
The speaker's actual impedance is 6 ohms or more over almost half of the audio range.
The bottom line is that bench tests are far more stressful to an amplifier than actual real world usage with speakers and music. Thus theories and suppositions about the capabilities of power amp power supplies that are based on bench testing with pure sine waves and resistive loads are hyper-conservative to the point of being nearly irrelevant.