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Per Channel Watts Specs for Home Theater Receivers (1 Viewer)

richatct

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Here is something I have always wondered about the RMS Watts spec of a home theater receiver.

Any time you view a spec (of any brand) of a multi channel receiver (let's say 7 channels), it is always written in this format:
"140 watts per channel into 8 ohms (20-20,000 Hz) at .08% THD, with 2 channels driven".

And I am like ok.... 90% of my use of the receiver are in watching movies or TV, which will typically be powering all 7 channels (not just two for stereo). But the spec talks about watts per channel with ONLY 2 channels driven.
So, does that mean I can get 140 watts X 7 channels?

Or if that spec is 140 x 2 = 280 watts, then in reality in using 7 channels at the same time I am actually getting: 280 watts / 7 channels = 40 watts for each of the 7 channels?
 

Gary Seven

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No, usually. The wpc spec is what it is capable of, not necessarily what it does. It depends on the power supply. Take the power supply total wattage divided by number of channels to get a better idea what it does for those channels.
 

JohnRice

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As Gary alluded to, that specs show the maximum each channel is capable of putting out, but you're completely right that it doesn't represent what can be produced running all channels. With most receivers, the power supply is exhausted driving two channels to their max. Unfortunately, they never give an all channels driven spec, so you can only speculate what it is.

In most cases, your math of 280/7 isn't far off. It probably isn't as low as 40, but it's probably no more than 60.

Keep in mind that surround channels don't require as much power, since they generally don't reproduce low frequencies. The lower the frequency, the more power needed to reproduce it.

Manufacturers have upped the ante on deceptiveness lately with a new rating that's a 1KHz tone at 10% distortion, one channel driven, rather than 20Hz-20KHz at a reasonable distortion level with two channels driven. That spec is completely BS. No connection to reality at all.

This is a major reason I use external amps in my main HT. The amps I have are able to provide full power to all channels, but they weigh a ton. In reality, that's overkill, since surround channels don't need as much power. That's why many amps, including the current versions of the ones I have, no longer are able to run all channels at 100% simultaneously. However, if you're looking at a two channel amp, you want full power from all channels. Same with a three channel amp for the front three channels in a surround system.
 

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