From: eric@prodigal.psych.rochester.edu (Eric Hansen)
Newsgroups: rec.audio
Subject: Re: Do I really need 200W?
Date: 29 Dec 92 15:02:49 GMT
Organization: University of Rochester - Rochester, New York

In <7009@otc.otca.oz> brendan@otc.otca.oz (Brendan Jones) writes:

>As to how many watts you need - I reckon not many.  I have a 25 W per channel
>true RMS class A power amplifier, and a comfortable listening volume is 2 to 3
>out of 10.
....
>So from this I think 25 W RMS is plenty, but it also depends on the other
>specs for the amp and the specs for the speakers you're connecting to it.

I recall a series of messages about a year ago where this guy was trying
to convince everyone that 2-5 watts was enough more most people.  This is
probably true in some respects, but to save time&bandwidth, I'll summarize
what I can remember from this posting stream...

To double the spl (sound pressure level) which you hear at your ear, you
pretty much need to increase the wattage going into the speaker by tenfold.
Hence, 50 watts will sound twice as loud as 5 watts.  For fun, you can
poke fun at your friends with 200wpc power amps by saying that their system
is only twice as loud as your Sears $129 rack system.

Anyways, this post turned into a huge debate about headroom and which wattage
ratings were most appropriate for different listening environments.

- If you're a DJ with a set of Gemeni speakers (or 4, or 5...) then you want
lots of watts so you can crank up your bass (and add a dbx subharmonizer with
sub?!?!)

- If your Joe-average who lives in an apartment with normal neighbors, then
you'll only be allowed to use your stereo at moderate levels anyways, right?
I would think that, while its nice to keep a "full tank" with 200 wpc, you
won't have the opportunity to use it.  100wpc.

Now the headroom plug...  true: dynamics require "headroom" which means
that the cannon blast in the 1812 overature will almost always make your
amp clip if its at a "kind of loud" level.  This is one of the all-time
classic clip tests.  I tried it a while ago with an older 200wpc amp and
a set of dbx SF-V speakers (from DAK, no less), and it clipped so badly
that I thought I had ruptured the speaker.  On the other hand, I could
always play REM "loud" -- it comes down to dynamics.  So I suppose this
brings up the issue of slew rate...  okay, forget I said that.

To summarize the preceeding babble:

For a two speaker system owned by conservative folk, "I think" <100 wpc
is perfectly appropriate.

For college fraternity parties and loud bachelor blowouts, 200 wpc is
preferable.  The more speakers you have, the more wattage you need.  A setup
with several smaller amps is probably more stable than one big amp.

For the typical "audiophile" which power-hungry 2,4,6 ohm speakers, 200 wpc
is good, too.  If you put importance on being able to listen to classical
music as respectable volumes (IOW, high), then clean, high power is desired.
Compare a Krell 100wpc amp with a mid-fi 200wpc amp...  the Krell won't
clip with the cannon blast.

Please note that the preceeding has little or nothing to do with sound
"quality"...  

"Just my opinion"

Eric Hansen
--
* Eric J. Hansen                       |    Center for Clinical Computing   *
|  eric@binoc.bih.harvard.edu          |   350 Longwood Avenue, Boston, MA  |
*  eric@prodigal.psych.rochester.edu   |            (617) 732-5925          *
Newsgroups: rec.audio