define rms

Home / the12volt's Install Bay / Car Audio / define rms (

Topic Closed)

Welcome Guest :)

Members

< Prev Topic Next Topic >

jr64

Member - Posts: 1

Joined: January 14, 2008

Location: Texas, United States

Posted: January 14, 2008 at 11:45 PM / IP Logged

I need to find out what the definition of RMS is when they say 250 watts RMS or when woofers say RMS/max power.

ice32

Copper - Posts: 116

Joined: June 12, 2007

Location: Australia

Posted: January 15, 2008 at 1:49 AM / IP Logged

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.

http://www.eznec.com/Amateur/RMS_Power.pdf

i'm not sure how accurate it is though

Alpine Guy

Platinum - Posts: 2,478

This member has made a donation to the12volt.com. Click here for more info.

Joined: October 18, 2003

Location: Canada

Posted: January 15, 2008 at 7:17 AM / IP Logged

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.

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.

KPierson

Platinum - Posts: 3,527

This member consistently provides reliable information

Joined: April 14, 2005

Location: Ohio, United States

Posted: January 15, 2008 at 7:45 AM / IP Logged

root mean square

Do a google search on the above and you'll have all the info you need!

http://en.wikipedia.org/wiki/Root_mean_square

Kevin Pierson

KPierson

Platinum - Posts: 3,527

Joined: April 14, 2005

Location: Ohio, United States

Posted: January 15, 2008 at 7:49 AM / IP Logged

Alpine Guy wrote:

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

sedate

Silver - Posts: 1,173

Joined: July 03, 2004

Location: Colorado, United States

Posted: January 15, 2008 at 8:11 AM / IP Logged

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

sedate

Silver - Posts: 1,173

Joined: July 03, 2004

Location: Colorado, United States

Posted: January 15, 2008 at 8:13 AM / IP Logged

Oh yea! Wikipedia is generally pretty useless, but that link above is pretty well fleshed out.

"I'm finished!" - Daniel Plainview

DYohn

Moderator - Posts: 10,741

This member has been recognized as an authority in Electrical Theory. Click here for more info.

This member has been recognized as an authority in Mobile Audio and Video. Click here for more info.

Joined: April 22, 2003

Location: Arizona, United States

Posted: January 15, 2008 at 8:19 AM / IP Logged

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

n2audio

Copper - Posts: 95

Joined: March 02, 2005

Location: United States

Posted: January 15, 2008 at 8:21 AM / IP Logged

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.

Sorry, you can NOT post a reply.
This topic is closed.

Printable version

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot delete your posts in this forum
You cannot edit your posts in this forum
You cannot create polls in this forum
You cannot vote in polls in this forum

Search the12volt.com

Follow the12volt.com

Disclaimer: *All information on this site ( the12volt.com ) is provided "as is" without any warranty of any kind, either expressed or implied, including but not limited to fitness for a particular use. Any user assumes the entire risk as to the accuracy and use of this information. Please verify all wire colors and diagrams before applying any information.

define rms

Sorry, you can NOT post a reply.This topic is closed.

Sorry, you can NOT post a reply.
This topic is closed.