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What does RMS mean


baszha

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36 minutes ago, baszha said:

I know that WPC means watts per channel,  but what does RMS mean and how is it used

 

RMS = Root Mean Square. It's a mathematical way of determining an "average" amplitude  of an alternating waveform such as sound produces.

John Kuthe...

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12 hours ago, JohnKuthe said:

 

RMS = Root Mean Square. It's a mathematical way of determining an "average" amplitude  of an alternating waveform such as sound produces.

John Kuthe...

Thank you John,

So which is a higher WPC....140 or say 275 RMS.  I am looking at a Emotiva XPA 3 cannel amp to power my fronts. The Emotiva puts out 275 RRMS. I am looking for 250 Wpc. but I am confused at how much wpc 275rms is.

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Guest wdecho

The RMS is a more accurate rating to judge power from amp. No matter what is said, you are buying way more power than needed for our horns. I assure you 25 true clean watts, preferable class A, are all that is needed. If you do not believe me it is easy to check power used with a AC volt meter at speaker. Play music as loud as you ever listen to and measure AC volts used on peaks. use this calculator http://www.ohmslawcalculator.com/ohms-law-calculator  and put ohms of speakers in one box and highest AC reading in the other box and calculate and be ready of a shock when you see less than 2 watts or thereabout on peaks. Nothing actually wrong buying Formula One car to go 70 mph if you have the money to spend though. 

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1 hour ago, baszha said:

So which is a higher WPC....140 or say 275 RMS.

Well of course 275RMS is higher than 140.  Plenty of headroom for your RF-82s and RC-62.  Your front speakers will never(rarely if ever) see anywhere near 275w/ch even with peaks.

 

Bill

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2 hours ago, JohnJ said:

I remember it being translated to laymans terms as rated minimum watts/channel.

Continuous wattage not the peak wattage that goes way higher.


Yep! And to handle those ridiculously high transient needs for audio power, the more cleanly powerful an amp you have the better. The ideal is to never require your amp to reproduce anything so powerful that will cause it to go into distortion.

PS: I have a Bachelor's degree in Electrical Engineering so I know "way more" about electricity and magnetism than most people. :-)

John Kuthe...

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On 8/6/2018 at 10:27 AM, JohnKuthe said:

Yep! And to handle those ridiculously high transient needs for audio power, the more cleanly powerful an amp you have the better. The ideal is to never require your amp to reproduce anything so powerful that will cause it to go into distortion.

Amen !!

Yep don't ask a machine or anything else to put out 90% + and you might not be disappointed with it.

 

Had one low powered 40 wpc continuous rms Nakamichi the I could put at 3 to 4 pm on the pot all day long and it never clipped.

Never had anything else I ran close to 2:00. Then again Nelson Pass designed that one.

I'm getting plenty of db at high noon on the current rig although I put it to 1:00 briefly before.

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1 hour ago, JohnKuthe said:

PS: I have a Bachelor's degree in Electrical Engineering so I know "way more" about electricity and magnetism than most people. 🙂

Awesome, another member with solid credentials.:emotion-21:

 

I only pretend sometimes that I know what I am talking about.;):P

 

Bill

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57 minutes ago, willland said:

Awesome, another member with solid credentials.:emotion-21:

 

I only pretend sometimes that I know what I am talking about.;):P

 

Bill

 

Well, I knew all this much (RMS and all, SWR too!) when I was in HIGH SCHOOL. I know a LOT about electricity and audio equipment theory too.


So much so I was the progenitor of a band in 1979 called Cheep Effects:
 


on which I played an old patch cord MOOG Synthesizer! Our first songs were done on my Pioneer CTf-1000 cassette deck with a separate playback and record head, and I connected a microphone and played back the tape monitor delay signal, which makes the coolest swoopy echoey sounds! I was playing with that when my friend from next door came over and I said Hey Craig! Check this out!

And Cheep Effects was born! 1979! Lasted a couple of 90min cassettes, two studio songs and that was about it! And I have most all the Cheep Effects stuff DIGITIZED and on my hard drive!

Cool stuff!! :-) I'm gonna sell it online someday soon. Hope too anyway.

John Kuthe...

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On ‎8‎/‎6‎/‎2018 at 4:34 AM, wdecho said:

The RMS is a more accurate rating to judge power from amp. No matter what is said, you are buying way more power than needed for our horns. I assure you 25 true clean watts, preferable class A, are all that is needed. If you do not believe me it is easy to check power used with a AC volt meter at speaker. Play music as loud as you ever listen to and measure AC volts used on peaks. use this calculator http://www.ohmslawcalculator.com/ohms-law-calculator  and put ohms of speakers in one box and highest AC reading in the other box and calculate and be ready of a shock when you see less than 2 watts or thereabout on peaks. Nothing actually wrong buying Formula One car to go 70 mph if you have the money to spend though. 

Thanks wdecho for the comment. I just want to make sure I have the power needed to run those speakers at their best.

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The question "how much amp power is adequate" cannot be answered without knowing:

  • The sensitivity rating of your speakers.  (Sensitivity is rated on a logarithmic scale.  As a result, different speakers can need significantly differing amounts of amplifier power.)
  • The size of your listening room
  • The types of music you listen to
  • Whether you listen to modern "hi-res" recordings that can have relatively high dynamic range (depending on genre)
  • Whether you use a powered subwoofer with crossover before the main amp, thereby off-loading the main amp and speakers
  • How loud you like to listen

FYI, many people who use high-sensitivity Klipsch speakers use tube amps with less than 10wpc.    (Because of different clipping characteristics, solid state amps generally need significantly more power than tube amps in order to perform satisfactorily.)

 

 

 

 

 

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9 minutes ago, JohnJ said:

Funky Feedback/Distortion there! @JohnKuthe


Thanks! We aimed not to please but to have fun and say some important things. I'm glad there were actual musical talented folks in our band who could actually PLAY instruments.

Our other studio song was much melodic and somewhat conventional. 

John Kuthe...

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RMS Root Mean Square

For the gory details check wiki  https://en.wikipedia.org/wiki/Root_mean_square

Can't really do a better job.  But basically squaring the voltage before averaging it over time (often a period if it is a simple waveform) , then taking the square root.  So all values are positive. 

 

The reason you square the voltage before averaging the values is because for power calculations,  Power is proportional to the square of voltage, so you have to give more weight to higher voltages.  In other words, if voltage is 2 volts for half the period, and 4 volts for the second half, you cannot simply average them to  (2+4)/2 = 3.  

You have to  take  square root of (4+16)/2  = square root 10 = 3.33     

 

For audio power it means using the RMS voltage of the signal, then using Power= V^2/R    where R is usually a pure 8 or 4 ohm resistor. 

 

So of you have a 10Volt amplitude signal (that is -10v to 10v) sinewave signal, the RMS value is 10/sqrt(2)  or  7.07 volts

to calculate the power into 8 ohms.. it is  P=7.07^2 / 8  

 

The term "rms power"  as used for audio is actually incorrect as you do not take the square root of the average of the square of power.  

The term implies "calculate power using the RMS voltage" 

 

If you had a varying signal as in real music, you could average out the power over time, but it makes no engineering sense to take the RMS average of power over time. 

 

 

 

 

 

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On 8/8/2018 at 10:12 PM, efzauner said:

The term "rms power"  as used for audio is actually incorrect as you do not take the square root of the average of the square of power.  

The term implies "calculate power using the RMS voltage"  

 

 

Correct.  Saying "RMS power" or "Watts RMS" is a misnomer -- there is no such thing as a "Watt RMS", but people have using it for so long that it have entered into the vernacular.

 

And the typical RMS calculation (peak voltage of the sine wave divided by the square root of two) is only true for sine waves.  For pure square waves the RMS voltage is the peak voltage.

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