watts (was: 7.1 preamp)

Levi Pearson levipearson at gmail.com
Sun Feb 27 19:27:21 MST 2011

On Sun, Feb 27, 2011 at 4:51 PM, Wade Preston Shearer
<wadeshearer.lists at me.com> wrote:
> My old AVR 635 has 75 watts per channel. Will I notice a drop down to 65 with the 2600?
> Also, does anyone understand (and could explain) the difference in the way that Harman Kardon calculates watts versus the rest of the industry? I've read that they do it differently and that an 80 w HK is equivalent to other systems listed at 110 w (per channel).

I can't speak to how anyone else does power ratings, but here's how HK
does, from their FAQ:

The gist of it is that they measure power output while driving all
channels with all frequencies (pink noise) simultaneously.

Whether you will notice a drop in potential output from 75W to 65W
will depend on what volume level you typically listen at and what kind
of sound you typically listen to.  If you listen to music with a lot
of dynamic range (i.e., not any pop music recorded in the last decade.
:P ) and listen to it loud, you might notice more distortion in the
transients.  Movies with loud sound effects might do it too, though
you probably won't notice a loud crashing noise distorting like you
would a musical note.

I'll bet, though, that 65W/channel will be plenty.  You've probably
got a powered subwoofer that will provide a significant portion of the
SPL in your system, and 7 channels at 65W each gives 455W total output
beyond the bass from the subwoofer.  Depending on the size of the
room, your seating location, and the sensitivity of your speakers, you
could still likely easily hit 85db SPL with plenty of headroom.  85db
is apparently where THX calibrates the center of a theater, so with
your system adjusted to 85db at your listening location while playing
the "THX sound" you'd have pretty much the same volume as a high-end

For more technical details on sizing amplifiers, see another Harman
page: http://www.crownaudio.com/amp_htm/amp_info/how_much_power.htm
There's a calculator linked from there that will give you the amp size
necessary for clean amplification to a given SPL.

BTW, I work for Harman International, though I don't currently work on
anything directly related to consumer-level amplifiers or speakers.  I
have played with some high-end Crown amplifiers though, and blew up
some not-so-high end JBL speakers with them. :)


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