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Old 24th October 2007, 11:20 PM   #1
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Default Strange results from Bassbox Pro - 23W4557

I'm tyring to model up a suitable enclosure for the Scan Speak 23W/4557T00 subwoofer. When running the number through BassBox Pro, the volume of the enclosure seems way too small (around 17L). Using other "web" programs, the volume given was 35-37L for Qtc=0.7. Can anyone give me any insight as to why there is such a variation?
Also, any views on what size sealed enclosure works best with this driver?
Thanks
Smithy
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Old 25th October 2007, 01:46 AM   #2
Ron E is offline Ron E  United States
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post the parameters.

Check against the simple calculation:
Fc/Fs = Qtc/Qts = sqrt(Vas/Vb+1)
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Old 25th October 2007, 02:27 AM   #3
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Here are the parameters:

Fs=20.5Hz
Qms=4.8
Vas=45.6L
Xmax=13mm
Sd=232 sqcm
Qes=0.52
Re=3.45 ohms

With Fc=34Hz and Qtc=0.7, then the volume by the formula you gave should be 37L, which is what I expect. In Bassbox pro, it gives 22.3L using "classical box calc" mode. If I add any fill to the box ("typical"), the suggested box dimension comes down to
16.6L
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Old 26th October 2007, 11:08 AM   #4
Ron E is offline Ron E  United States
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There are few programs at any price that have a good model of the effects of stuffing on a sealed box enclosure. Bassbox is an overpriced program with few real features that free programs don't have. Bassbox 5 used to have really gross errors in its Port/PR calculations (related to area). Bassbox 6 was a redo of the math, but it is telling that the price of Bassbox keeps dropping. Why anyone would use it for a reference is beyond me.

Small-Margolis (JAES, 1981) is the accepted simple way to model the effects of stuffing a sealed enclosure. The equations were developed with fiberglass as a damping material. The method actually gives similar results to a full resistive model (as better freeware like Unibox and WinISD "PRO", and presumably Bassbox 6, use) but with simpler math.

An undamped, simple Q=.707106 solution gives:
Undamped ---- Vb=36.1, Fc = F3 = 30.8

Small Margolis gives the following Q=0.707 results for your woofer:
Lined (2-3") --- Vb=28.1, Fc= 33.2
Stuffed --------- Vb=18.4, Fc=35.9

My own purely resistive simulation gives:
Assuming Ql=10, Qa=20 (lined):
Vb=24.5, Fc=34

Assuming Ql=10, Qa=10 (stuffed):
Vb=22, Fc=36

My resistive model does not assume any volume increase from using damping material, only resistive damping. I don't claim this to be a "better" model than any other, but you can see the results are more conservative. I am an isothermal-adiabatic unbeliever, for now.

I honestly doubt you would hear much difference between a 18 and 22 liter box. These things are not so finicky as the calculations make them out to be. The accuracy with which your woofer fits the T/S model (and to which you can measure the parameters) is probably on the order of 5-10% anyway. There is nothing wrong with making your box a little bigger and unless you measure Ql and Qa with your choice of damping material, you will always be working with an assumed value. I have never seen a study which validates any of the assumed values commonly seen in programs (even mine ) which calculate stuffing effects. Be thankful that in the end it doesn't matter much.
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Old 26th October 2007, 11:33 AM   #5
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Thanks for your comments. Appreciate you taking the time to do some calcs & gives me a good feel on which way to go.
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