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Old 18th March 2012, 01:17 AM   #1
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Default PK Sound CX800: 95% efficient??

Anyone heard of/seen PK Sound's CX800 high powered subwoofer? Some popular dubstep/edm artists (Caspa, Bassnectar, etc) choose this sound to tour with for low end reinforcement. PK claims 139 dB peak output (133 dB continuous) and +/- 3dB from 28Hz - 150Hz. 2500W and up to 95% efficiency. Dual 18" neo drivers w/28mm xmax.

CX800

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Old 18th March 2012, 05:42 AM   #2
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An amplifier may have 90% efficiency, but a speaker may not.

The most efficient woofer that I know of is the JBL 2220 at 8.7%, and it has NO BASS.

In general, the less efficient a driver is, the more maximum output it will have in the bass.

Their claims look like total BS, and I know an independent lab could not duplicate them.

A 2 cu ft 2nd order sealed box with an F3 of 30hz can only be 0.18% efficient (84.55dB).
A 2 cu ft 4th order vented box with an F3 of 30hz can only be 0.36% efficient (87.56dB).
A 2 cu ft 6th order vented box with an F3 of 30hz can only be 0.90% efficient (91.54dB).

The net cabinet volume here is less than 14 cu ft, so the maximum efficiency at 30hz will be on the order of 96dB/W/1M. 96dB + 34dBW (2.5KW) is 130dB.

Where did the other 9dB go?

What about power compression?

If it is a 6th order vented design the mid-band output could be 4dB higher, but the bottom 1/3 octave will be 2dB less (assuming the power output is limited by power rather than excursion.

Did you know that a degree in marketing allows you to change the laws of physics by a factor of 10:1 to your advantage?

That seems to be in effect here.

PS

The x-max is at best a P-P value.
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Old 18th March 2012, 07:46 AM   #3
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http://www.eighteensound.it/renderPdf.aspx?pid=288

You run the numbers and see if I am correct.
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Old 18th March 2012, 05:41 PM   #4
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the speakers look like 18 sound,
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Old 19th March 2012, 01:27 AM   #5
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That's why I posted the data sheet.

I would have used the 9000 before the 9600 though.
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Old 19th March 2012, 01:47 AM   #6
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Quote:
Originally Posted by djk View Post
An amplifier may have 90% efficiency, but a speaker may not.
On reading the details, the 95% efficiency claim does seem to be in connection with the amplifier used in the powered version of the sub, not its acoustic output.
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Old 19th March 2012, 03:13 AM   #7
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I realize that, but their other claims are entirely fact-free.
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Old 19th March 2012, 03:23 AM   #8
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I realize that, but their other claims are entirely fact-free.
Well, I won't say that they're "fact-free". Perhaps "Optimistic" :-)

For example, they didn't say how the box was loaded to get that peak SPL figure (2PI, 1PI, 0.5PI?). And some do quote peak-to-peak Xmax...
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Old 19th March 2012, 04:50 AM   #9
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That's why I posted the data sheet.

I would have used the 9000 before the 9600 though.
whats wrong with the 9600?
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Old 19th March 2012, 06:49 AM   #10
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"they didn't say how the box was loaded to get that peak SPL figure"

Well they did state that the response was FREE FIELD RESPONSE, which I would assume to mean 4Pi (flown), but they should state that they actually meant on the floor, in the corner (0.5Pi), if that is what they meant.

Calculating the No=4.12% from T/S parameters comes up with 98dB/W for the pair of drivers, but the box size is a little on the small side.

"whats wrong with the 9600? "

Nothing , other that the Qts is a bit low for a vented box.

Max efficiency, minimum size, and max bass extension comes with a Qts=0.312
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Last edited by djk; 19th March 2012 at 07:06 AM.
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