How do i figure out watts & rms as i usually estimated guess?

Question

i have a home amp thats 600w how do i figure out how many rms it is as i no watts dont mean anything important,normally i just guess an usally get pretty close on my conversions.in saying that i would GUESS its only bout 270w rms,so how do i actually find out the correct answer?

Answer 1

Good question - but power with speakers is a bit complex.

Here are some facts:

- It takes more power to the same volume at 80 hz, than 8,000 hz.  So power output depends on what sounds you are producing at any instant. Honest companies specify power ratings from 20 - 20,000

- Distortion: You can force an amp to give more power, but something called "Total Harmonic Distortion" increases to audible levels fairly quickly beyond the rated value. Good numbers are like 0.07%

- Impedance: A 4 ohm speaker will draw twice the power as an 8 ohm speaker. Some companies measure power with a 4 ohm speaker to make the amps appear more powerful.  Good companies publish power numbers with 4,6,8 ohm, non-inductive loads to avoid the confusion.

- On average your amp puts out only 5-7 watts per speaker. (No joke.) But to increase the volume by 1 db you have to double the power.  This is why we need 70-120 watts per channel - to handle large volume swings.

- Peak vs RMS: (already covered by other answers)

- Stereo vs all channels driven: Some companies publish power numbers in BIG LETTERS and small print says "2-channel or Stereo mode" so the amp is only driving 2 speakers, not 5.

WHENEVER YOU SEE POWER NUMBERS FOR AN AMP:

Look for answers to these questions:

How many speakers, Peak vs RMS, What frequency range, 4,6 or 8 ohm speakers, What amount of distortion?

Answer 2

First off, good guess.

Watts *do* mean something important: they are a measure of power (to do work). The work being done is the speaker drivers pushing and pulling against the ambient air, creating sound waves.  It requires more power to move larger speakers, and to move larger quantities of air by increasing the cone's excursion (by crankin' it!).

The confusion is caused by stereo equipment manufacturers that print marketing material which hypes the *peak* or *maximum* (instantaneous) power handling of their speaker drivers, expressed in "watts"; true enthusiasts are more interested in knowing the *continuous* power handling, usually expressed in "watts RMS".

RMS stands for "root mean square" and is related to the math used to calculate that rating.  The math is too complicated to describe here properly, but a Web search should help you find formulas *and* explanations (it's good to understand why things are done certain ways).

Your guess seems alright; in general, you can assume the continuous power handling is no more than half of the instantaneous (AKA peak), and typically less than half.

The manufacturer should have detailed specs available through their website for modern equipment; vintage equipment might be more difficult to spec.

If you can't find much info, you may know the values of enough "variables" to plug them into equations for calculating RMS power.

Answer 3

An amp that's rated at 600W (peak) would be 424W (rms).  RMS is 70.7% of the peak.

Answer 4

The math is correct in the first answer. Erms = Epeak x .707

Since our ears are basically RMS devices, peak power has no value in real terms, for audio. The value is in marketing.

Let's suppose you are a buyer for CostCo or Walmart and you want to maintain your appearance of "low price leadership" in the marketplace, and at the same time make a good profit. One of the easiest ways is to provide a lower grade product and make it look equal to a better product to the unsuspecting consumer.

Major manufacturers play into this game by providing special lines of surround receivers that have their wattage rated at peak instead of rms. Most major manufacturers have their line of high quality surround receivers for the Electronics retailers and custom installation companies. All wattage ratings are accurately stated in rms. They also have another line of cheap surround receivers for the discounters and the Internet etailers that have their wattage measured at peak. Regardless of the manufacturer, these lower-end devices are designed from the ground up with cost cutting in mind, instead of performance, while maintaining the appearance of being equal to their higher grade counterparts.

I hope that I was clear with regards to this deception. Although the manufacturers play along, it's really driven by Costco, Walmart, Target, etc... Etailers have jumped on this profit train too!

Sorry to get a little off subject, but I thought it would be valuable to understand why the useless "peak" rating is employed sometimes.