What is RMS?

[Gadgeter]

Taken from another website:

 

R.M.S. stands for "root mean squared", which is your mathematical way of finding the average (ergo "mean") output power of an alternate electric signal.

 

10 Watts RMS at 4 ohm, for example, mean than an amplifier can output a clean 10 watts of sound into a 4 ohm speaker, in the full audio range, thus being it's realistic power.

 

 

Also note that there is a big difference between Peak (PMPO) and RMS.

 

Peak, as the name says, will indicate, the max power it can have. So 10 Watt Peak at 4 ohm mean that an amplifier max output will be 10 watts of (probably distorted) sound into a 4 ohm speaker, at the perfect frequence(s).

 

So it is important to always check the RMS value of a speaker or an amp before buying. If only the peak value is indicated, RMS value is always at 70% of the peak.

 

 

p.s: If you have a more detailed write-up, please post.

Edited April 4, 2005 by Gadgeter

[Luckcent]

you must be a sound engineer. cheerio....

[Gadgeter]

Paiseh, I'm not engineer... Not trained in this field..

[Luckcent]

hahahahaha........

[Soya]

labels that scream "1000W" means nothing as that's onli the split second power the component can handle. RMS is a better gauge of a systems' power. kinda like a car's bhp and torque (more useful) figures.

[Luckcent]

might as well say it in kilo watts......like cars...

[Headshok]

BUt sometimes, RMS also cannot trust, some amps are under-rated, they can say " 50 watt RMS", but it will kick the ass out of your speakers..

 

so, gotta see brand also..

 

also.. now everything all made in CHINA, see beh sian.. then only thing the sales pple at sim lim tell u is that the amp is QC by ang mo. but still made in either china or korea. SO, gotta see where its made.. if made in US or aniwhere else other than china, comfirm sound diff..

[Luckcent]

purchase amps made from uk....they are reliable, also speakers too.....

[Endless373]

"BUt sometimes, RMS also cannot trust, some amps are under-rated, they can say 50 watt RMS, but it will kick the ass out of your speakers..

"

 

I guess it gotta do with the voltage that the RMS power is measured in. I suspect many car audio manufacturer rate their amp according to 14.4V. While some rate it at 12V which definitely gives a lower rating.

[Tploh]

The "1000W" is calculated on the sum of the max power of all components, including all the fancy bulbs. That's why some unit has more lights than others, so that it can claim higher Watt (PMPO).

 

It is only a marketing gimmick. Don't fall for it.

[Nissantoot]

Yeap. The most accurate is to check out what the RMS output power of the amplifer is. It is the averaged power (root mean square). The power of the speakers must also be matched to the amplifier output.

 

Typically, for sales gimmicks, the product will show the instantaneous power rating. That is the maximum power output which the product can sustain for an instant (usually milliseconds according to electrical time constants). This happens when there is an unusual say, high pitch or bass in the music piece. But if such unusual spikes are prolonged, then saturation (sound distortion) or the burn-out of the power supply will take place.

 

PM me if you need more details...

[York]

Typically, for sales gimmicks, the product will show the instantaneous power rating. That is the maximum power output which the product can sustain for an instant

 

old thread digging....yes...tt is wat on the market currently...a lot of AMP in PMPO...which is 60 to 70% of the RMS..

[Slonez]

The RMS is much lower than 60-70% of the PMPO rating.

Remember those mini compo with 2000 watts PMPO rating, I don't think their power is any where close to 25% of their PMPO rating (assuming the same impedance), not to mention 60-70% .

[Khfoong]

impressive

[York]

the mini component...using a lower impedance, that why the power's jacked up in "K"...

For auto amp..most of the time...audio experts assess the peak output as 50% of RMS power with clean voltage supply in 12V....as the voltage increase to 14.4V(most vehicles) when engine is running..can expect an increase on the output by 10 to 17% depending on the make...so 60 to 70% is onli an estimation(not to disgrade too much on the 'peak power' amp)

[Normal_aspirated]

i oso no scientist........taken from a website:

The RMS value of a function is often used in physics and electronics. For example, we may wish to calculate the power P dissipated by an electrical conductor of resistance R. It is easy to do the calculation when a constant current (I) flows through the conductor. It is simply,

 

1) P = I(square)xR

 

But what if the current is a varying function I(t)? This is where the rms value comes in. It may be shown that the rms value of I(t) can be substituted for the constant current I in the above equation to give the mean power dissipation, thus:

 

2) P = I(square)(rms)xR

 

In the common case of alternating current, when I(t) is a sinusoidal current, as is approximately true for mains power, the rms value is easy to calculate from equation (2) above. The result is:

 

3) I(rms) = Ip divided by square root of "2"

where Ip is the peak amplitude.

 

The RMS value can be calculated using equation (2) for any waveform, for example an audio or radio signal. This allows us to calculate the mean power delivered into a specified load. For this reason, listed voltages for power outlets (e.g. 110V or 240V) are almost always quoted in RMS values, and not peak values.

 

In the field of audio, mean power is often (misleadingly) referred to as RMS power. This is probably because it can be derived from the RMS voltage or RMS current. Furthermore, because RMS implies some form of averaging, expressions such as "peak RMS power", sometimes used in advertisements for audio amplifiers, are meaningless.

Edited July 29, 2005 by Normal_aspirated

[Yankee_eric]

it's informative....think many people were conned by salesman on the power rating of their hifi......

[Tploh]

Do yoiu remember a few years back, once mini-compo with many lights were very popular ?

 

Why ? Because all the light bulbs help to add to a higher PMPO. I heard that PMPO is all the watttage added up in the system. I.e. if you have more light bulbs, you use more wattage. And thus a higher PMPO rating.

 

Please correct if this is inaccurate.