define rms
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=101173
Printed Date: May 01, 2024 at 10:35 AM
Topic: define rms
Posted By: jr64
Subject: define rms
Date Posted: January 14, 2008 at 11:45 PM
I need to find out what the definition of RMS is when they say 250 watts RMS or when woofers say RMS/max power.
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JR
Replies:
Posted By: ice32
Date Posted: January 15, 2008 at 1:49 AM
To my understanding the basic meaning of RMS is the constant power required at normal running volumes.
Im sure theres a more detailed description or more accurate one out there, so maybe some of the audio professionals here can help you out.
rms is the more accurate of the power figures, out of rms and max.
If you wanna read up on it, this pdf seems pretty informative from what i scrolled over.
https://www.eznec.com/Amateur/RMS_Power.pdf
i'm not sure how accurate it is though
Posted By: Alpine Guy
Date Posted: January 15, 2008 at 7:17 AM
RMS is 70.7% of the peak power the amplifier can produce. What does this tell you? It tells you that pretty much every audio companie out there lies about their peak numbers. Thats why you follow rms ratings, not peak.
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2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.
Posted By: KPierson
Date Posted: January 15, 2008 at 7:45 AM
root mean square Do a google search on the above and you'll have all the info you need! https://en.wikipedia.org/wiki/Root_mean_square ------------- Kevin Pierson
Posted By: KPierson
Date Posted: January 15, 2008 at 7:49 AM
Alpine Guy wrote:
RMS is 70.7% of the peak power the amplifier can produce. What does this tell you? It tells you that pretty much every audio companie out there lies about their peak numbers. Thats why you follow rms ratings, not peak.
Based on my understanding of RMS it is NOT always 70.7% of the output of an audio amp or speaker. RMS is the average output over the entire frequency range. Since audio output is not a constant frequency (like AC line voltage) it would be impossible to assign a costant value to a system that is constantly changing. I may be wrong on this, but thats my take. ------------- Kevin Pierson
Posted By: sedate
Date Posted: January 15, 2008 at 8:11 AM
Alpine Guy wrote:
RMS is 70.7% of the peak power the amplifier can produce
Where did you get this figure? KPierson wrote:
Since audio output is not a constant frequency (like AC line voltage) it would be impossible to assign a costant value to a system that is constantly changing
Close. You can simply average a changing number, but with AC voltage, you are really measuring a wave - with positive and negative values - averages here are not useful because the negative magnitude of the wave will mathematically make the positive magnitude of the wave look like a net of ~0 if it were simply averaged. So we arrive at the quadratic mean - the root mean square, as an appropriate measure of waveform power. ------------- "I'm finished!" - Daniel Plainview
Posted By: sedate
Date Posted: January 15, 2008 at 8:13 AM
Oh yea! Wikipedia is generally pretty useless, but that link above is pretty well fleshed out.
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"I'm finished!" - Daniel Plainview
Posted By: DYohn
Date Posted: January 15, 2008 at 8:19 AM
In reality there is no such thing as "RMS power." RMS or root mean square only applies to AC voltage and AC current and not to power at all. RMS voltage and current together create power, but calling it "RMS power" is a misuse of the term. RMS voltage is basically the DC equivalent of an AC signal and is, for a sine wave, the peak value divided by the square root of 2. "Average power" or "continuous power" is a better name for it than RMS power. "Max power" is typically the peak amount the gear can sustain for a short period of time and is not a very useful rating to use when designing a typical everyday driver system. Always use Average power ratings. ------------- Support the12volt.com
Posted By: n2audio
Date Posted: January 15, 2008 at 8:21 AM
what is specified for an amplifier's output power isn't technically RMS (.707 peak). It is maximum continuous power w/o clipping. It's measured using a sine wave. Another item of note regarding power -- even highly dynamic music only requires about 1/3 the power of a test tone at full volume. So if an amp can produce, for example 500w ("rms") playing a test tone at full volume it will only produce 100-200w playing music at full volume.
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