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