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Author Topic: RMS Vs PROGRAM  (Read 27937 times)

Bryan Hampton

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RMS Vs PROGRAM
« on: November 17, 2004, 10:48:52 AM »

Can someone tell me what the difference is between RMS & program. I read somewhere that program power, is basically the continous power that the speaker manufacture recommends, and that with an RMS power rating that you should add 1.5 to 2 times the RMS wattage for maxium SPL. Is this true? I'm basically trying to figure out how many watts I need for the following speaker combination:

(2) 800 watts program (4 ohm) tops
(2) 800 watts program (8 ohm) subs

also tops can be biamped

(2) 200 watts program (4 ohm) HF horn
(2) 800 watts program (4 ohm) LF driver

Thanks for your help
Bryan
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Don Boomer

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Re: RMS Vs PROGRAM
« Reply #1 on: November 17, 2004, 11:16:05 AM »

Program watts has come to mean a doubling of the continous wattage rating of an amp.

The idea is that music is rarely/never on all the time so the thought is the heat created in a speaker is about the same when considered as Program watts as it would be if the power applied to a speaker using a continous signal and the contioous wattage figure.  There's your doubling.

What you expect from a speaker's rated figure is the basis for what comes next.  Are you looking at the power spec as ... the amount of power needed to make the speaker perform at maximum capacity ... the amount of power you can apply before speaker burnout?  Well the answer to either is not so simple.

Most power amps can deliver the equlivalent of double their continous/RMS/EIA (etc) power when driven to clipping as compared to their clean sine wave output.  One of the reasons you can burnout a 100W speaker with a 100W (or even down to nearly half of that) amp is because it can produce 200 watts of heating up the voice coil.

If you get a bigger amp, lets say double (200w) and you keep the amp below clipping there is less strain on the speaker.  That's true IF and only if you absolutly keep the amp from clipping ... because if you clip that amp you are now delivering  400W to the speaker.

The other thing is when does that 100w speaker burn out ... if you hit it with 105 watts for 10 hours straight ... or ... if you hit it with 200 watts for seconds.  The answer ... well nobody knows, it all depends.

If you supply a potentially too big amp and you do something stupid like runaway feedback or plugging a line level signal (like from a CD) into a mic input, you could have some big problems quickly.  If you just expect too much from the system and just drive it a little too hard, a little too long, same thing.  It will burnout eventually.

Lots of other things to consider as well but this post is getting rather long.
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Don Boomer
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Line 6, inc.

John Roberts {JR}

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Re: RMS Vs PROGRAM
« Reply #2 on: November 17, 2004, 03:22:17 PM »

boomer wrote on Wed, 17 November 2004 10:16

Program watts has come to mean a doubling of the continous wattage rating of an amp.



Generally Program relates to speaker not amplifier power.

boomer wrote on Wed, 17 November 2004 10:16


clip----

Most power amps can deliver the equlivalent of double their continous/RMS/EIA (etc) power when driven to clipping as compared to their clean sine wave output.  One of the reasons you can burnout a 100W speaker with a 100W (or even down to nearly half of that) amp is because it can produce 200 watts of heating up the voice coil.

If you get a bigger amp, lets say double (200w) and you keep the amp below clipping there is less strain on the speaker.  That's true IF and only if you absolutly keep the amp from clipping ... because if you clip that amp you are now delivering  400W to the speaker.



This is only true in the extreme. Yes an X watt amplifier would measure 2X watts hard clipped all the way to a square wave, but even the most tin eared newbie would back off before that much overdrive. What is true is that you can deliver more than 1x nominal power by hard clipping music.

boomer wrote on Wed, 17 November 2004 10:16


The other thing is when does that 100w speaker burn out ... if you hit it with 105 watts for 10 hours straight ... or ... if you hit it with 200 watts for seconds.  The answer ... well nobody knows, it all depends.

If you supply a potentially too big amp and you do something stupid like runaway feedback or plugging a line level signal (like from a CD) into a mic input, you could have some big problems quickly.  If you just expect too much from the system and just drive it a little too hard, a little too long, same thing.  It will burnout eventually.

Lots of other things to consider as well but this post is getting rather long.



This has been much discussed with lots of useful discussion in the archives. The problem boils down to the power content of musical waveforms being quite variable and not simple to quantify  in terms of sine wave or continuous power. To take advantage of  usable peak speaker excursion you expose yourself to the risk of  being able to overheat the voice coils with too much average power. There is no fool proof solution and user restraint is a good idea.

JR
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Bosstard

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Re: RMS Vs PROGRAM
« Reply #3 on: November 17, 2004, 03:35:24 PM »

Quote:

 I'm basically trying to figure out how many watts I need for the following speaker combination:


What the others have said is true, but heres help directly related to your question of powering. Yes, you normally want 1.5-2x the power of the RMS ratings. So when you pick out an amp you want something between the program and clipping power ratings. Since clip is normally double the program rating an amp between 800 and 1600 watts will work. However you should stay closer to the program rating then clip. An amp that will do 1000watts into 8 ohms would work fine for tops, and an amp that will do 1000watts into 4 ohms would work for your subs. The QSC PLX3402 would work for the subs and the QSC RMX 5050 would work for your tops. Hope this helps.


Steven.
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Marty McCann

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Re: RMS Vs PROGRAM
« Reply #4 on: November 17, 2004, 04:53:09 PM »

In the past some manufacturers have used their own (in a few cases swamp gas) criteria for these specifications.  However the accepted International Standard is outlined in the AES (Audio Engineering Society) Standard #2-1984.  The rated power of the device is the continuous power that the device can withstand for 2 hours without permanent change in acoustical, mechanical, or electrical characteristics greater than 10%.

Basically according to this standard the Program rating is twice that of the Continuous, and the Peak rating is four times that of the Continuous.  Now the Caveat of the standard is that the rating is contingent upon having a minimum of 3 dB of amplifier headroom available.  This (at least in my mind) is an audio world diccotomy (not unlike Schrodinger's Cat experiment)  in that there may be some conflict between what the standard tells us about the behavior of the transducer in a laboratory test and what we may experience to be true in our particular audio application.  In other words YMMV.

Let me try to explain in (nearly) semi-technical terms.  Let's say that the loudspeaker is rated at 500 Watts Continuous.  That would then be 1000 Watts of Program Material, and 2000 Watts of Peak Power handling . . . BUT in order to meet the 3 dB Headroom criteria of the standard, one must use a 4,000 Watt Amplifier and maintain 3 dB of Headroom above the Peaks.  Since uncompressed Live Music has a Peak to Average Crest Factor of somewhere between +14 to +20 dB above where the envelope settles down or where the Program Averages, then this is now somewhat of a Leaning Out Of the Window Contest (one in which you can't win for losing).  Practically every Weekend Warrior would Blow-UP a 500 Watt Continuously rated speaker if he were to drive it with a 4,000 Watt amplifier.  This is why (generally) the average user should probably have an amplifier as least as big as the Continuous rating of the loudspeaker, but probably NOT more than the Program rating.

It may now be as clear to some as a Turkish Coffee (Hint:  You don't drink Turkish Coffee, you TAKE it).  But then I am sure there are others who get the bigger picture.

marty
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Don Boomer

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Re: RMS Vs PROGRAM
« Reply #5 on: November 17, 2004, 05:27:01 PM »

In other words ... curiosity might have killed the cat  Very Happy
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Don Boomer
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Line 6, inc.
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