Xref: utzoo rec.autos:10412 sci.electronics:3260 rec.audio:7146
Path: utzoo!yunexus!geac!sq!utfyzx!utgpu!water!watmath!clyde!att!ihnp4!twitch!guido
From: guido@twitch.UUCP ( G.Bertocci)
Newsgroups: rec.autos,sci.electronics,rec.audio
Subject: Re: Car stereo RMS power
Summary: Power of sine wave is not peak to peak
Keywords: Bridged amps, DC-to-DC converters
Message-ID: <1068@twitch.UUCP>
Date: 11 Jul 88 13:48:02 GMT
Article-I.D.: twitch.1068
References: <5244@ihlpf.ATT.COM>
Organization: AT&T Bell Labs, Holmdel, NJ
Lines: 29

In article <5244@ihlpf.ATT.COM>, chrz@ihlpf.ATT.COM (Chrzanowski) writes:
| >I wrote:
| >Sine wave is + and - so that gives you + and - 6 volts peak to peak.

My apologies, peak to peak is not the  right term.
I was indicating that the sine wave would be 6*sin(x) volts.
As opposed to 4.24*sin(x) volts rms.
| 
| 	[No.  It can vary from zero to +12, that's 12 volts peak TO PEAK]
| 
| >6 / 1.41 = 4.24 V RMS which yields ~4.5 Watts into 4 ohms.
| >Since cars are usually above  13 Volts you get slightly more than
| >5 watts  per channel.  If you want more than 5 watts you need to
| 
| To convert volts peak to peak (VPP) to RMS (assuming a sinewave)
| >Try dividing by 2 and then divide by the square root of 2 
| Soo, If we've got 12 VPP into 4 ohms then RMS power is
| 
| 	(12volts * 12volts) / ((2*(2**.5) * (4ohms)) = 12.7 watts.

Since your are squaring the voltage you need to square the part under
the division sign too.

	(12volts * 12volts) / (((2*(2**.5)**2) * (4ohms)) = 4.5 watts.

-- 
Guido Bertocci			...!ihnp4!twitch!guido
AT&T Bell Labs
Holmdel, NJ