what does 100watt rms mean???

Answer 1

R.m.s. is a mathematical operation applied to alternating voltage or current in order to arrive at the d.c. value which gives the same heating effect.

It is wrong to apply the term to power. Yes, I know many people do so, but it is, nevertheless, technically incorrect.

In practice the term is (mis)used to mean continuous average power and assumes that the device is being driven by a sine wave.

You may find this of interest http://www.davidbridgen.com/watts.htm
The first article, on another site, is the easier to understand.


With reference to the previous post, the peak power from an amplifier driven with a sine wave is twice the continuous average power.

Shawn Z is shooting himself in the foot.
He says "the RMS value is the amount of power that can be outputted continuously."

Yes. And while an amplifier is giving that continuous output, the peak of that same output is twice that average. It's a fact. Like it or not . I give figures later in this post.

Again .... the peak value of a sine wave is 1.414 the r.m.s.

The peak value of the power is calculated from the peak value of the voltage, you can't multiply the average power by 1.4.

Shawn is confusing the peak value of the continuous power and the peak NON REPETITIVE power, which is a different matter entirely.

His "I've seen some amps claim 100w of peak power, only to be able to output about 20W of RMS" is an example of this. The claimants fail to tell you that 100W is the non-repetitive figure. The actual peak power of a continuously rated 20W amplifier is 40. And yes, it may well produce 100 or even more, NON-REPETITIVELY.

And again, he says "A good, quality amp will be rated in RMS primarily, and will peak roughly 30-50% over the RMS value."

NO. The peak power will ALWAYS be twice the continuous.

It is the instantaneous NON-REPETITIVE PEAK, which will be higher.

Put another way, the continuous power will ALWAYS be half the peak. But it will certainly NOT be half the non-repetitive peak.

It is ESSENTIAL to differentiate between the peak and the non-repetitive peak.

Shawn's "A bass note can hit quickly, but not that often, so it can make use of peak power. A low rumble that is more continuous will make use of the RMS power" is at best misleading, and to the novice meaningless.




And, with reference to Robert P's post, which follows this one .....

He says "To convert RMS value to peak value ,divide by 0.707"

Yes. Or multiply by 1.414.

But remember what I said at the beginning of my post - r.m.s. is an operation applied to voltage or current.

Let's look at some figures.

We have an amplifier which is applying a sine wave of 20Vrms to a load. The load is 8 ohms.

The power in the load is therefore 50W.

The peak value of the applied voltage is 28.28.

The power in the load at that point is 100W. Twice the average.

[n.b. with reference to the additions I made earlier .... the non-repetitive, instantaneous, peak power of that amplifier, may well be (much) higher, but that is nothing more than a red herring.]


You seem to suggest that the peak power would be 1.414 times the continuous (your "r.m.s.") power.

You see the difficulty you get yourself into?


R.m.s. is a mathematical operation applied to alternating voltage or current. NOT power.

Answer 2

If you still wonder what it really means, the RMS value is the amount of power that can be outputted continuously. A bass note can hit quickly, but not that often, so it can make use of peak power. A low rumble that is more continuous will make use of the RMS power.

Generally, car amplifiers claim twice the RMS power for the peak power, although this really just implies a cheaper amplifier. I've seen some amps claim 100w of peak power, only to be able to output about 20W of RMS. A good, quality amp will be rated in RMS primarily, and will peak roughly 30-50% over the RMS value.

The next post does not take into account the build quality of some amplifiers. in a perfect world, I would agree, that the peak power is 2x the RMS. Since amps are made differently, many of them very cheap, the peak power can be 3-4x the RMS value, which can be much lower than expected.

Answer 3

JR got it right "Root Mean Squared"

It is a more 'honest' way of measuring the power output from a receiver.

Since sound is a sine-wave (rolling up and down), power is also a sine-wave.

You could measure the power of an amp by measuring the peaks. Many low-quality receiver companies do. But to truly calculate the power, you must take the average under the curve. One technique is the Root Mean Squared.

Answer 4

Hi. There are two ways of expressing power,Peak and RMS.Peak power is the Amplifier's ability to provide an instantaneous burst of power .However,peak power measurements are somewhat fictitious since they cannot be sustained for long. RMS stands for Root Mean Square.RMS power ratings are a mathematically correct way to express an Amplifier's usable average power,which is a representation of real - world performance . There is a lot of disagreement in audio. A specification of 100 watts RMS means nothing unless the Amplifier bandwidth ,impedance, number of channels, and total harmonic distortion are included with the power output. The term "Continuous"is sometimes used instead of RMS because it is more accurate.

HERE IS AN EXAMPLE OF AN AMPLIFIER WITH THE CORRECT POWER SPECIFICATIONS :

100 watts,Continuous,per channel 20 to20,000 Hz @8ohms,5 channels driven, with no more than 0.01% THD.


HERE IS AN EXAMPLE OF AN AMPLIFIER WITH INSUFFICIENT POWER SPECIFICATIONS :(You should avoid buying this type of amplifier)

100 watts,Continuous per channel ,1.k HZ @8 ohms,1 channel driven,with no more than 0.01% THD

Answer 5

Don't waste your money adding a power amp to your current sub. The speaker is designed for that amp and can not up grade. You normally will not run a subwoofer for a very long time at that high level of volume. Hope this will help you out.

Answer 6

I think it means 100 watts of continuous power verses peak performance.

Answer 7

It could mean 100 Watts Power root mean squared, but I'm not for sure.

Answer 8

damn DMB, I was gonna answer this but I dont think I have too anymore.