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Author Topic: Peak to RMS Ratio  (Read 11812 times)

David Sturzenbecher

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Peak to RMS Ratio
« on: July 23, 2014, 09:58:33 am »

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?
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Corey Scogin

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Re: Peak to RMS Ratio
« Reply #1 on: July 23, 2014, 11:26:07 am »

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?

How are you calculating the power ratio?  See the attached image for the correct formula and this page for more details: http://www.sengpielaudio.com/calculator-db.htm
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Hayden J. Nebus

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Re: Peak to RMS Ratio
« Reply #2 on: July 23, 2014, 11:30:17 am »

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?

Might you be confusing field quantities, which you should square/ or multiply the log by 20, with energy quantities, for which you should multiply the log by 10?

I've made that mistake myself. 
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Geoff Doane

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Re: Peak to RMS Ratio
« Reply #3 on: July 23, 2014, 01:16:40 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?

Power compression? Although 6 dB seems like a lot.
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David Sturzenbecher

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Re: Peak to RMS Ratio
« Reply #4 on: July 23, 2014, 01:23:26 pm »

Might you be confusing field quantities, which you should square/ or multiply the log by 20, with energy quantities, for which you should multiply the log by 10?

I've made that mistake myself.

Yup that was it right there, I was using 20 log instead of 10 log. Thanks for the refresher.
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Don Boomer

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Re: Peak to RMS Ratio
« Reply #5 on: July 24, 2014, 02:29:18 pm »

The 6 dB difference between peak and average would be in line if all you were putting into the speaker was sine waves.  But of course you are likely never doing that unless all you play back is test tones.   

The newest AES speaker power handling spec now calls for 12 dB as live music as an input almost always has more than 6 dB peak to average ratio.
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Don Boomer
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Hayden J. Nebus

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Re: Peak to RMS Ratio
« Reply #6 on: July 24, 2014, 03:59:40 pm »

The 6 dB difference between peak and average would be in line if all you were putting into the speaker was sine waves.  But of course you are likely never doing that unless all you play back is test tones.   

The newest AES speaker power handling spec now calls for 12 dB as live music as an input almost always has more than 6 dB peak to average ratio.

A pure sine has a crest factor of 3dB. AES2-1984, which called for pink noise with crest factor 2 (6dB) has been superceded by AES2-2012, which calls for pink noise with crest factor 4 (12dB).

 Some manufacturers may not rate their products to this standard, or to the previous standard. Buyer be informed!
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Art Welter

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Re: Peak to RMS Ratio
« Reply #7 on: July 25, 2014, 02:21:33 pm »

The newest AES speaker power handling spec now calls for 12 dB as live music as an input almost always has more than 6 dB peak to average ratio.
Don,

Thanks for the heads up, had not noticed the introduction of  AES2-2012.

Seems odd that the 6 dB dynamic range AES2-1984 has been superceded by the 12 dB dynamic range AES2-2012 when the general trend since that time has been progressively more, rather than less, dynamic compression in pop music.

Some EDM even has less than 3 dB dynamic range in the sub 100 Hz range, the  AES2-2012 would grossly inflate the potential of a sub handling that type of music.

Art
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Hayden J. Nebus

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Re: Peak to RMS Ratio
« Reply #8 on: July 25, 2014, 03:35:31 pm »

Don,

Thanks for the heads up, had not noticed the introduction of  AES2-2012.

Seems odd that the 6 dB dynamic range AES2-1984 has been superceded by the 12 dB dynamic range AES2-2012 when the general trend since that time has been progressively more, rather than less, dynamic compression in pop music.

Some EDM even has less than 3 dB dynamic range in the sub 100 Hz range, the  AES2-2012 would grossly inflate the potential of a sub handling that type of music.

Art
Art,
It's actually a more conservative rating, all other things being equal. I'd assume the intent was to make the noise signal more closely simulate the peak-to-average power found in live signals.

If you're trying to drive those EDM signal peaks all the way up to the AES2-2012 loudspeaker's peak power rating, sure, you're going to have a bad day. You've exceeded rated continuous power handling. But if you drive the RMS level of that same 3dB crest signal up to the loudspeaker's continuous power rating, you actually have more headroom than a transducer rated at the same continuous power under the prior '-1984 rating.

If you drive a AES2-1984 rated transducer and an AES2-2012 rated transducer together with 6dB crest pink noise up to their respective continuous power handling ratings (using RMS metering), the AES2-2012 rated transducer will still have 6dB headroom, which the other transducer will not. If you drive them with 12dB crest pink at that same RMS drive level, the  '-2012 rated transducer will run, while the '-1984 rated transducer will probably crap out sooner than later, from having been driven 6dB beyond its peak power handling. 

Here's to more conservative ratings.

EDIT: revised power handling language  per Dave's correction

 
« Last Edit: July 25, 2014, 07:23:04 pm by Hayden J. Nebus »
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Dave Gunnell

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Re: Peak to RMS Ratio
« Reply #9 on: July 25, 2014, 05:26:20 pm »

...while having a 12dB peak to RMS power rating...
...You've exceeded rated RMS power handling...up to the loudspeaker's RMS power rating...more headroom than a transducer rated at the same RMS power...

...up to their respective RMS power handling ratings (using RMS metering)

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... :).
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ProSoundWeb Community

Re: Peak to RMS Ratio
« Reply #9 on: July 25, 2014, 05:26:20 pm »


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