DC Power supply question...duh...

From: Dave Dameron <ddameron_at_earthlink.net>
Date: Fri Jul 2 22:01:37 1999

At 11:07 PM 7/2/99 +0100, Tony wrote:

>What I was really asking is for any kind of justification of the '240W'
>figure. Now, most of these speakers seem to have a 6W DC input rating, so
>the output power can't be any more than that.
>
>I wonder if it's something like :
>
>We have a 12V PSU. So we can get 24V p-p across the speakers (use a
>full-bridge output stage). Say 8 ohm speakers, 4 of them (2 per channel).
>So we get 24^2/8 *4 = 288W. Yes, I know there's absolutely _no_
>justification for any of that, but then again it is marketroid-speak....
>
Boy does that sound like spec. inflation! 24 p-p is just 12 Volt peak in
either polarity with a bridge circuit. That gives 12/8 peak amps and 18
peak watts (like with a +/-12 volt square wave). The RMS voltage and
currents are these voltages, currents divided by sqrt(2), giving a sine
wave power of 9 watts per 8 Ohm speaker, with no voltage drop in the
amplifier. Don't tell me these "240 Watt" speakers are powered by 4 "AA"
batteries ;)... or use one of the many automobile ic amps that give about
4.5 watts with a 12 Volt supply and a 4 Ohm speaker.
-Dave
Received on Fri Jul 02 1999 - 22:01:37 BST