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Please explain RMS??

Hi guys, joined the forum after seeing so many helpful replies to other peoples' posts. I'm wondering if you can help me understand RMS.

If a speaker system says something like "20W RMS", what is it actually telling me it can do?

Also, what if an all-on-one iPod speaker system sort of thing has two 10W speakers, does that mean it outputs 20W?

 

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Re: Please explain RMS??

RMS is mesure Peak output, I can't explain fully but I am sure someone will come along and explain it better than me. The contineous rate is the one that you should be looking for....20W RMS is about 4 real world watts (per channel)

Anonymous
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All numbers are merely indicative

user="JazzHands" wrote:

Hi guys, joined the forum after seeing so many helpful replies to other peoples' posts. I'm wondering if you can help me understand RMS.

All numbers are merely indicative.

That should be a standard disclaimer printed in all manuals of AV equipments Smile Oh well, you asked about RMS.

RMS - is an acronym for Root Mean Square. As such Root-Mean-Square is a general concept in school level mathmetics. If you insist much on theory here is it: http://en.wikipedia.org/wiki/Root_mean_square

To keep the matters simple, RMS is used to express the power handling capability of an amp or a loudspeaker system. Notice the phrase loudspeaker system. The RMS value is expressed, generally, is of the whole loudspeaker system and not of a single driver. That makes it easier for consumers to understand the whole system as a whole. Otherwise, an end user will have to know maths and physics to calculate the RMS value of a loudspeaker system.

When a manufacturer says, this loudspeaker's power handling capacity is 20 wrms, he means to says, this loudspeaker (system) is capable of handling 20 watts of power (again, thats a complex calculation, if a load lets 1 ampere of current pass thru given 1 volt, it is said to be a 1 watt consumer, save for loudspeaker load). Simply put, the RMS value is an indication of how much currenton a long-term basis a loudspeaker can take. Notice the phrase long-term basis. Usually, the voice coil of a transducer will be able handle a lot more power on a short-term basis than it can on long term basis. Why? Because, that will be an instantaneous attack (order of a 1000th of a second or so).

 

user="JazzHands" wrote:
If a speaker system says something like "20W RMS", what is it actually telling me it can do?

It is saying, it will be able to handle power equivalent of 20 watts on a long-term basis (implies, it will perform best with an amplifier that generates 20 on a long-term basis)

user="JazzHands" wrote:

Also, what if an all-on-one iPod speaker system sort of thing has two 10W speakers, does that mean it outputs 20W?

 

Depends on the what exactly manufacturer wrote. If he said - 10 watts per channel and it has two channels it means 20 watts equivalent. But if he didn't indicate clearly, it may well mean the system has 10 wrms of output.

Anonymous
Anonymous's picture
Re: Please explain RMS??

RMS stands for Root Mean Square and will give an 'average' value, as opposed to a peak value (it will be the equivelent dc heating power), for a sine wave. This works out to be 0.707 of the peak value for a sine wave.

Anonymous
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Re: Please explain RMS??

user="JazzHands" wrote:

Hi guys, joined the forum after seeing so
many helpful replies to other peoples' posts. I'm wondering if you can
help me understand RMS.

If a speaker system says something like "20W RMS", what is it actually telling me it can do?

Also, what if an all-on-one iPod speaker system sort of thing has two 10W speakers, does that mean it outputs 20W?

 

But,
the honest truth is: you will not benefit by reading my previous post.
What will help you is: to see whether the dock has a sweet sound that
you like well enough, and to see whether the sound is loud enough to
fill the room you will keep it in.

The matter of fact is: 20
watts is phenomenal power, if you ask me. You don't expect your iPod
doc to explode the roof of your house, do you? if you don't then that's
enough power. Those tine driver in iPod docks are pretty efficient. 10
wrms of power is way more than they will need.

Just look for the
sound quality and try placing your dock in a place, it can get it's
sound to reinforce (under your workstation, or may be in a cub-board and leave the slider open a bit).

Anonymous
Anonymous's picture
Re: Please explain RMS??

 Ranjeetrain, thanks for such an in-depth bit of advice! It seems to me that RMS figures can be used to confuse a consumer into buying something.

 

Anonymous
Anonymous's picture
Re: Please explain RMS??

My feeling is that RMS would be more representative of power handling than things like 'peak music power' and the such like.

I guess as long as like for like is compared it should give an indication, but be wary of manufacturers defining their own particularly high methods for specifying them.

Also, i think the output current might be useful to know (if its documented) to give an indication of how transients might be handled.

hth

Bloney

Anonymous
Anonymous's picture
Re: Please explain RMS??

The best available measure for the output of an amp is its RMS output value.

The current is a useful piece of information as it "tells" you how well the amp will drive real speaker loads and possibly how well it will deal with transients.

Values like "peak music power" and "maximum peak mega blasto power" are generally meaningless - above noted that peak power is 1.4*RMS power which is true.  Less scrupulous (or more desperate) manufacturers quote ridiculous things like 200 watts pmpo from systems that probably put out less than 10 watts rms.  So exactly what they're quoting is known only to them but needless to say it represents little meaningful.

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