Originally Posted by Joji
I am going to buy a new receiver for my home theatre. I read up on some info but a little confused. When you say all channels driven does this mean that a 140 watt amp all channels driven is 7 separate 140 war amps so each amp would take care of each speaker individually.
also most pioneer Elite receivers now say 140 watt per channel. is this the same. I don't want the signal to be spread across all the amps I want each amp to power each speaker individually.
Then the new pioneers speakers say the they were tested at 1k instead os 20hz-20k like the older Elite receivers. I thought the 1k thing was a gimmick. I want the best sound quality
First of all, any multichannel amplifier indeed has multiple amplifiers, each connected to it's own speaker outputs. There is no way in our phyusical universe for a single power amplifier to accept multiple different inputs and output them to different places. It's a one-in-one-out proposition for the power amp. Power output depends on a number of factors, including the capability of the output amplification devices (transistors in this case) and as indicated above the power supply available. Let's assume a pair of transistors in push pull for each separate amp. A pair that is specified by their manufacturer to be able to make 100 watts at X distortion can only do so when they have the appropriate cpower available to them. So if I take a 100 watt output transistor set and connect it to the power supply of a preamp that needs to deliver a mix of 2 watts or so, the power transistors will not be able to hit 100 watts. The reason a lot f receivers cannot output full 2 channel rated power into 5 or 7 channels is their power supplies just aren't robust enough to serve all those amps at onece WHEN THEY CALL FOR FULL POWER. Using movies as an example, the "typical" dialog level of 85 dB at reference requires, and will use only, 1/100 of the power needed to play back peaks (105 dB per speaker).
Generally modern receivers use the exact same output devices for every channel. FTC rules establish how to determine power and because of a quirk in the wording, multichannel amps need only be able to hit ther specified levels with 2 channels driven, most manufacturers figure. So that's what you should expect.
If the specification says 100 watts per channel at 1% distortion, all channels driven, it mearns, really, that the MFR says the amp can make 100 watts through each amp all at the same time. You don't see receivers specified this way and third party testing shows they are absolutely all over the place as to how much of their rated power they can hit with multiple channels operating, or at lower impedance (which stresses the output devices more . . .)
So with a typical receiver, if the program material every actually maxed out in all channesl at once (and you needed full 2-channel rated power to hit those levels) you would get significant distortion, and probably not the full 140 watts or whatever from any channel (and you don't really want to listen to 140 watts at 10 or 15 % distortion unless it's a distorted electric guitar and you're a goodly distance away from the speakers). But real world movie material doesn't (so they say) peak in all channels simulteneously, so it is not as big an issue as it might seem at first glance. Many of us (like me) listen at lower than reference levels, requiring significantly less than full power even for the loud parts.
But really the only way to know the output capability of any of these devices is to test them yourself (something I could not do) or read independent third party testing. There are too many variables that the manufacturer can fiddle with to goose up their power ratings. They do that because it's what sells, and beccause it's what everybody else does and it's hard to educate consumers that "my 50 wpc all chanels driven is superior to brand X's 120 wpc, 2 channels driven." Easier just to play the game the way it is played.