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Author Topic: Peak to RMS Ratio  (Read 11941 times)

Hayden J. Nebus

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Re: Peak to RMS Ratio
« Reply #10 on: July 25, 2014, 07:14:51 pm »

There's actually no such thing as 'RMS Power.'  You probably mean 'long term' or 'continuous power', but in a strict sense the term 'RMS Power' has no real meaning.

Bob Lee at QSC authored a white paper that touches on the subject of this misnomer... :).

You're absolutely right, thanks!  I meant to refer to the signal's RMS level and the loudspeaker's continuous power rating, respectively .

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Peter Morris

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Re: Peak to RMS Ratio
« Reply #11 on: July 25, 2014, 10:22:49 pm »

I have been creating a spreadsheet of subwoofers I commonly use in designs, and I came to notice that many models (almost all) have a 6dB peak to RMS SPL rating, while having a 12dB peak to RMS power rating.  Can anyone give insight on why there is a difference?

I very simple terms, the continuous or RMS power or whatever you want to call it, is more or less the thermal capacity of the driver. The peak power is representative of the mechanical strength of the driver. The program power is roughly the recommend maximum RMS input you should use. It allows for the fact that music is not continuous so you donít have thermal problems.

For example, my subs use 2 of these - http://www.eighteensound.it/PRODUCTS/Products/ProdID/58/CatID/8#.U9MCSmkiPq4
i.e. 3,600 watts continuous, 7,200 watts program, 20,000 watts peak. Ö or roughly 20 horse power for a pair subs a side!

They can sustain their program rating provided they not pushed below 30 - 32 Hz, at which point they exceed Xmax. Once you exceed Xmax the impedance drops, the cooling provided by the voice coils proximity to the magnet structure drops, and it all goes pear shaped Ė the smoke that powers the speaker can then escape  :-\.
 
The change from 6 dB to 12 dB crest factor was to reflect real world conditions better; musicís dynamic range is more like 10 Ė 20 dB,  itís very rare (not impossible) to find peak to average ratios less than 6dB.
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Ivan Beaver

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Re: Peak to RMS Ratio
« Reply #12 on: July 25, 2014, 10:54:43 pm »


 
The change from 6 dB to 12 dB crest factor was to reflect real world conditions better; musicís dynamic range is more like 10 Ė 20 dB,  itís very rare (not impossible) to find peak to average ratios less than 6dB.
It all depends on what you call "music".

A lot of current popular music (EDM-RAP etc) has a very low crest factor-and at times is nothing but basically a sine wave.

It can be VERY hard on loudspeakers (especially subs).

In my opinion-it would be better to rate speakers using the 6dB rule-because it gives the "average" user a more conservative power rating.

Sure-less "bragging" rights-but what is the number there for anyway?  To me it should be to give the user an idea of what they could reasonably use in terms of a power amp to power them.

Yes many will disagree-but that is my feeling.  I try to take the conservative side when it comes to specs-allowing the average user to actually be able to achieve what is on the spec sheets.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

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David Sturzenbecher

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Re: Peak to RMS Ratio
« Reply #13 on: July 25, 2014, 11:26:07 pm »

Ivan, is there something special about the DBH-218? From my math, which could be wrong, it only shows a 3dB ratio on the power side, but a 6dB ratio on the SPL side


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Ivan Beaver

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Re: Peak to RMS Ratio
« Reply #14 on: July 25, 2014, 11:40:20 pm »

Ivan, is there something special about the DBH-218? From my math, which could be wrong, it only shows a 3dB ratio on the power side, but a 6dB ratio on the SPL side


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Actually the numbers are correct-but maybe a bit misleading.

The power is stated in continuous and program (NOT peak), while the SPL numbers are given in continuous and peak.

But the truth is this is actually a "typo" (kinda) left over from the days in which we did not state a "peak" power-just continuous and program.

We did not want to play the "peak" game-but since everybody else was giving peak numbers-we decided to add that also.

I will get it changed next week.

Thanks for the heads up.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Art Welter

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Re: Peak to RMS Ratio
« Reply #15 on: July 26, 2014, 02:21:42 pm »

For example, my subs use 2 of these - http://www.eighteensound.it/PRODUCTS/Products/ProdID/58/CatID/8#.U9MCSmkiPq4
i.e. 3,600 watts continuous, 7,200 watts program, 20,000 watts peak. Ö or roughly 20 horse power for a pair subs a side!
The peak rating is only for a duration of 10ms, one cycle at 100 Hz, only 1/2 cycle at 50 Hz ::).
That would be a short set...
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Ivan Beaver

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Re: Peak to RMS Ratio
« Reply #16 on: July 26, 2014, 06:38:31 pm »

The peak rating is only for a duration of 10ms, one cycle at 100 Hz, only 1/2 cycle at 50 Hz ::).
That would be a short set...
A good example of what happens when you look at the "simple numbers"-without an understanding of where they come from or what they actually mean.

I know one manufacturer who gives power ratings on how much it would take to physically break the driver in a cycle or two.

YEAH-that is how I want to power my rig-NOT.

I believe what the power ratings should REALLY mean would be to give the user an idea of what sort of size amplifier they could reasonably use to drive the speaker without damage.

Of course there are many other "unknowns" that could quickly skew the real world-such as highly compressed music-long extended shows (like 72 hours nonstop-no breaks-no set changes etc)/

Things like that can be REAL abusive on loudspeakers as the heat just continues to build up.

So you HAVE to take the numbers-then apply a bit of "common sense" to what YOU are doing at the moment and go from there.

But of course that takes an understanding and a little bit of knowledge-things that are sorely lacking in our industry ;(
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Peter Morris

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Re: Peak to RMS Ratio
« Reply #17 on: July 26, 2014, 09:32:35 pm »

The peak rating is only for a duration of 10ms, one cycle at 100 Hz, only 1/2 cycle at 50 Hz ::).
That would be a short set...

Yes but that's only to give an indication of the mechanical strength of the driver - 18sound provides a complete set of specifications - AES power, program power, peak power, thermal compression @ full power, -3db & -10dB, Xmax ... and specify how each are measured .... what else do you want ?????
« Last Edit: July 26, 2014, 09:47:54 pm by Peter Morris »
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Ivan Beaver

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Re: Peak to RMS Ratio
« Reply #18 on: July 26, 2014, 09:48:02 pm »

Yes but that enough to give an indication of the mechanical strength of the driver - the thermal capacity is the AES continuous, and neither of these consider Xmax ...

18sound provides a complete set of specifications, AES, program, peak, thermal compression @ full power, -3db & -10dB, Xmax and specify how each are measured .... what else do you want ?????
The "average consumer" just wants to know how many watts will it handle.

Don't confuse them with specs they don't understand.  They want a simple WRONG answer-but yet want to "believe" that the simple number tells them everything they want it to.

NOT!!
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Peter Morris

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Re: Peak to RMS Ratio
« Reply #19 on: July 26, 2014, 10:54:47 pm »

The "average consumer" just wants to know how many watts will it handle.

Don't confuse them with specs they don't understand.  They want a simple WRONG answer-but yet want to "believe" that the simple number tells them everything they want it to.

NOT!!

The average consumer is not buying these drivers from 18sound ;) .. they are buying completed boxes with every bit of spin the marketing department can get away with, and it seems to be getting worse.

The person that is buying these drivers would want all this information, and in some cases more ... which 18sound, B&C etc. can all provide.
« Last Edit: July 26, 2014, 11:02:44 pm by Peter Morris »
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Re: Peak to RMS Ratio
¬ę Reply #19 on: July 26, 2014, 10:54:47 pm ¬Ľ


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