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Relation between RMS and Max Wattage?

post #1 of 10
Thread Starter 
I have looked around teh interwebs for a good while looking for a relation between RMS and max wattage and what I have found has confused the He** out of me...

Is there any equation that relates these two or is my original assumption correct that the max wattage is about double the RMS?

Thanks in advance guys!
post #2 of 10
Quote:
Originally Posted by h0thead132;14387526 
I have looked around teh interwebs for a good while looking for a relation between RMS and max wattage and what I have found has confused the He** out of me...

Is there any equation that relates these two or is my original assumption correct that the max wattage is about double the RMS?

Thanks in advance guys!

on average max watts is double the rms. but now always. rms is the constant supply of power. where max wattage is a peak or burst of wattage that can be handled
    
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post #3 of 10
Its the same in the audio world, max is usually double RMS, RMS is continuous wattage. RMS is the ONLY value you want to go by when it comes to audio, as for computer stuff, I'm sure it would be the same. RMS is Root Mean Square, its essentially the formula for calculating continuous wattage.
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post #4 of 10
Using a RMS formula calculates the wattage (or it can be voltage) when dealing with a wave form other than straight DC. In AC power you are dealing with a sine wave (constantly variable in amplitude over time). The old formula for wattage, P=IE is not accurate when dealing with any wave form other than straight DC.

P= power (in watts) I = current (in amps) E= voltage (in volts) this is a formula when dealing with DC electricity.
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post #5 of 10
Generally well rated amplifiers will tell you RMS rating, per FTC spec of 20Hz ~ 20KHz, at a certain T.H.D. (Total Harmonic Distortion - This is important as well!)

Stay away from amplifiers that only specify max/peak wattage.

With good efficient speakers, you don't have to have a huge amp. It helps to calculate the sensitivity rating of speakers, and choosing the right amp with in the power rating of the speakers.

Just avoid clipping at all cost! It will ruin your tweeters quicker than anything. Clipping is when you push the amp too hard, beyond it's RMS rating.

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

Clipping:
http://en.wikipedia.org/wiki/Clipping_%28audio%29
Edited by Hoodcom - 7/29/11 at 7:57am
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post #6 of 10
Quote:
Originally Posted by PCCstudent;14391234 
Using a RMS formula calculates the wattage (or it can be voltage) when dealing with a wave form other than straight DC. In AC power you are dealing with a sine wave (constantly variable in amplitude over time). The old formula for wattage, P=IE is not accurate when dealing with any wave form other than straight DC.

P= power (in watts) I = current (in amps) E= voltage (in volts) this is a formula when dealing with DC electricity.

Vrms*Irms=P in an AC system and assuming a sine wave source,
Vmax is Vrms*(1/.707).

That doesn't work for current in the speaker as the speaker doesn't have constant impedance so finding max power from the RMS power would be very complicated and I have no idea how you'd go about doing it.
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post #7 of 10
Thread Starter 
ok... wow, you guys went above and beyond with this... lol

what my deal is is that i have a really crappy pair of speakers that are 5 1/4" woofers from an old bookshelf system that blew up on me a few years ago, what i was gonna do is pick up a sub amp from amazon or parts express and build a box for them and wire them in series so the resistance is decreased. I found the perfect amp for it but according to my math the speakers will be getting 93.3333.... watts rms for the pair at 3 ohms. On the back of the speakers it says that the operating range for them is 60-100Watts, now is that there RMS or Max, i assumed max and was then wondering if i got this amp would these speakers blow up?

I don't think it would seeing as each speaker would be getting 46.6666... Watts RMS which is below their max.
post #8 of 10
I did not even notice I was in the audio section.My electronics training is not audio heavy (I know I should be able to move from simple AC/DC circuits to audio but it is not happening) but audio is a bit of a different world,we did not cover the analysis of audio system ratings very heavy but I did work all those formulas over and over for the simpler (meaning where impedence was not such a great factor)AC/DC digital,radio theory circuits,I bow out when it comes to audio.The sales guys sure can manipulate things when it comes to audio systems. I was not trying to imply that my simple PIE formula would work with out some major tweaking with audio.
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post #9 of 10
To complicate matters for the OP, keep in mind that higher RMS does not mean louder/better music. That's going to depend on the efficiency rating of your speakers, which is usually measured at 1 watt RMS at 1 meter, in decibels. To make matters even HARDER to understand, decibels are not linear. It's a logarithmic unit.

Here's an example to explain how decibels work:

decibel-level.gif
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post #10 of 10
Looking at that chart and the db's for gunshots explains why I lost hearing in one ear when brother in-law popped of a 30-30 right next to my ear.Terrible headache.This was in the day of no hearing protection.He got the jack though.
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