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[Mark Hobbs]

Pascal Pincosy wrote on Wed, 08 August 2007 13:38

Mark Hobbs wrote on Wed, 08 August 2007 18:29 Keith Erickson wrote on Wed, 08 August 2007 02:41 JBL tests their speakers as a system (meaning the whole enclosure, X/O, etc.)  They don't just put 2 woofers that handle X amount of watts into a speaker and say it now handles 2X watts. Thats makes sense, but how do you explain the MRX and JRX having double the power handling for the dual 15 cabs as compared to the single 15 cabs? Don, Steve, and Chris already gave you the correct answers: 1) There is likely a crossover between....

Here is the story. I have been pestering JBLs so called tec department (not much of a tec department considering that every time I ask something they need to go check with the engineers and get back to me) and what I was told is that the reasoning behind the power handling is due to heat build up. When run at 3200 watts (double the SRX715s power handling...not 5000 or 6000 watts) for 100 hours they will fail due to heat...2400 on the other hand they will be fine. Much more than that and you may run into problems. There is NO XOVER or anything between the 15s, they are just wired in parallel and are playing THE SAME frequencies and they see THE SAME amount of power. Furthermore, they share the same enclosure...no seperate chambers for each diver. He said that the 2 motors from the 2 speakers in the SRX725 generates alot more heat than the SRX715 does with the single 15 inch driver and that has alot to do with the SRX725 not handling twice the power of the 715, where as the MRX and JRX just plain don't generate much heat per driver in comparison the the SRX hence the ability of the dual 15s cabs in the MRX and JRX line to handle twice the power of the single 15 counterparts.

[Don Boomer]

Brad Weber wrote on Tue, 07 August 2007 21:44

Don Boomer wrote on Tue, 07 August 2007 18:59 Passive power handling = LF drivers power handling in biamp mode See ... THAT doesn't make sense.  The passive power handling should always be higher than the power handling of the woofer alone because not all the power you put in gets to the woofer.  Some of the power is sent to the tweeter and some of the power is dissipated by crossover losses. It makes total sense for the passive full range power ratings to be equal to or even less than the LF driver ratings and this is very standard.  A crossover is a frequency divider, not a power divider (although passive crossovers typically do pad down the signal going to the HF driver to match the driver ratings).  The whole point of a crossover is to not have both drivers reproducing the same thing, so they do not share the load, so to speak.  If you put in a 100Hz signal, what part of that input power is being sent to the HF driver?  So the passive rating is typically that of the highest driver rating.

I think you misunderstand how the power handling figures are derived.

First the tests use shaped noise ... not a single frequency ... that makes a huge difference.  

Take a typical 2 way system , let's say rated at 400W.  When you apply 400W (of that shaped noise) to the input jacks typically you'll only see 180 to 300 of those watts actually reach the woofer.  It depends on how steep the filters are and how efficient the crossover is.  At the same time that 400 watts is sitting on the input jack only 20 to 40 watts reaches the terminals on the HF driver.

[Don Boomer]

I believe what was meant to be said was that they can't be fairly compared to other products that are rated using only the 2hr test.

Yes ... be maybe not in the direction that you might think at first ...

Let me set the record straight about power testing.

The EIA (RS-326A) test that is used by JBL calls for shaped WHITE noise to be applied for 8 hours.  White noise has a naturally occuring 3 dB/oct rise.  First order filters (6 dB/oct) are applied at 40 Hz and 320 Hz.  In this way the max power is delivered at about 320 Hz and is 13 dB down at 20 Hz and 12 dB down at 20 kHz.  Here's the deal ... it doesn't stress a speaker as much as live music does in the extremes but it is longer.

The AES 2-1984 standard that we use here at Peavey uses PINK noise and runs for two hours.  It is band limted at 20 and 20K with 2nd order Bessel filters.

The PINK noise (equal energy /octave) instead of WHITE noise (equal energy per frequency) means that the low frequency content is very strong by comparison.  Also the highs aren't attenuated until a very high frequency the high content is also very strong.  The AES test is much more difficult at the extremes.

As far as the length of the test.  In all honesty speakers reach an equalibrum after about an hour or so and while it sounds like 100 hours is more strenuous than two hours it hardly makes any difference in the real world.

Draw your own conclusions ... many experts have argued about it for a long time

[Bob Leonard]

Don Boomer wrote on Thu, 09 August 2007 17:50

I believe what was meant to be said was that they can't be fairly compared to other products that are rated using only the 2hr test. Yes ... be maybe not in the direction that you might think at first ... Let me set the record straight about power testing. The EIA (RS-326A) test that is used by JBL calls for shaped WHITE noise to be applied for 8 hours.  White noise has a naturally occuring 3 dB/oct rise.  First order filters (6 dB/oct) are applied at 40 Hz and 320 Hz.  In this way the max power is delivered at about 320 Hz and is 13 dB down at 20 Hz and 12 dB down at 20 kHz.  Here's the deal ... it doesn't stress a speaker as much as live music does in the extremes but it is longer. The AES 2-1984 standard that we use here at Peavey uses PINK noise and runs for two hours.  It is band limted at 20 and 20K with 2nd order Bessel filters. The PINK noise (equal energy /octave) instead of WHITE noise (equal energy per frequency) means that the low frequency content is very strong by comparison.  Also the highs aren't attenuated until a very high frequency the high content is also very strong.  The AES test is much more difficult at the extremes. As far as the length of the test.  In all honesty speakers reach an equalibrum after about an hour or so and while it sounds like 100 hours is more strenuous than two hours it hardly makes any difference in the real world. Draw your own conclusions ... many experts have argued about it for a long time

No argument from me Don, the PV test is valid and I had always thought pretty equal to the JBL testing method. I would be concerned with "other" so called 2 hour tests though.

[Brad Weber]

Don Boomer wrote on Thu, 09 August 2007 17:17

I think you misunderstand how the power handling figures are derived. First the tests use shaped noise ... not a single frequency ... that makes a huge difference.

No, I understand the test procedures, although many people do probably think that a X Watt rated speaker means you could apply X Watts of any signal to it.  They also tend to look at the continuous rating, not realizing that the test signal used represents a 6dB crest factor and that many real world sources have higher crest factors.

Quote:

Let me set the record straight about power testing. The EIA (RS-326A) test that is used by JBL calls for shaped WHITE noise to be applied for 8 hours. White noise has a naturally occuring 3 dB/oct rise. First order filters (6 dB/oct) are applied at 40 Hz and 320 Hz. In this way the max power is delivered at about 320 Hz and is 13 dB down at 20 Hz and 12 dB down at 20 kHz. Here's the deal ... it doesn't stress a speaker as much as live music does in the extremes but it is longer. The AES 2-1984 standard that we use here at Peavey uses PINK noise and runs for two hours. It is band limted at 20 and 20K with 2nd order Bessel filters. The PINK noise (equal energy /octave) instead of WHITE noise (equal energy per frequency) means that the low frequency content is very strong by comparison. Also the highs aren't attenuated until a very high frequency the high content is also very strong.

I am having a little trouble understanding this.  I believe that AES2-1984 (AES Recommended Practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement) that you referenced is intended for rating loudspeaker components, not full range loudspeakers.  The standard defines using pink noise bandwidth limited to one decade (from the LF point up one decade with the limits at the -3dB points and 12dB/octave Butterworth filters), a 2 hour period, a free air mounting and with the power calculated based on the measured RMS voltage and Zmin.  It might be applied to driver sections, testing one 'section' from 100-1,000Hz and another from 1,000-10,000Hz would seem within the standard.  However, the requirements of the standard, or at least the version I have, seem to limit the application to full range testing.  Has the standard been revised recently or might it actually be a different standard or some derivative of the standard being applied?  I am curious as a test with 20-20,000Hz bandwidth and Bessel filters appear to vary significantly from the standard.

I agree that the ANSI/EIA RS-426-A (EIA Loudspeaker Power Rating Full Range) and IEC 268-5 (International Standard - Sound System Equipment, Part 5: Loudspeakers) used by most manufacturers for reporting full range loudspeaker power ratings do use different shaped noise sources and longer periods along with several other differences in the procedures.  But they are intended specifically for full range testing.  It does seem that manufacturers who use the IEC or ANSI/EIA ratings for full range speakers do typically identify a passive full range rating equal to the rating of the LF driver, perhaps because they usually use the same test procedure for rating each section of the speaker as they do for rating the full range performance (which is different than the procedure used to test the drivers themselves).  

Quote:

The AES test is much more difficult at the extremes. As far as the length of the test. In all honesty speakers reach an equalibrum after about an hour or so and while it sounds like 100 hours is more strenuous than two hours it hardly makes any difference in the real world.

I guess it may depend on whether you are looking at mechanical or thermal failure.  The data I have seen from speaker manufacturers who publish test results for multiple procedures don't really support these statements.  In fact, I've seen some products stating around a 10% reduction in the power ratings for IEC 100 hours versus IEC 8 hours.

Quote:

Draw your own conclusions ... many experts have argued about it for a long time.

With the different spectra, bandwidth limiting, basis of calculated power, etc., between the different standard testing procedures, I'm not sure how much direct correlation can really be applied between devices using different rating procedures, especially comparing driver ratings to box ratings.  Probably the one truth is that if the marketing department has their say, the test procedure used will be provides the biggest number as the result.