Strange results from Bassbox Pro - 23W4557
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 24th October 2007, 11:20 PM #1 smithy666   diyAudio Member   Join Date: Mar 2001 Location: Sydney 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
 25th October 2007, 01:46 AM #2 Ron E   diyAudio Member     Join Date: Jun 2002 Location: USA, MN post the parameters. Check against the simple calculation: Fc/Fs = Qtc/Qts = sqrt(Vas/Vb+1) __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley
 25th October 2007, 02:27 AM #3 smithy666   diyAudio Member   Join Date: Mar 2001 Location: Sydney 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
 26th October 2007, 11:08 AM #4 Ron E   diyAudio Member     Join Date: Jun 2002 Location: USA, MN 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. __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley
 26th October 2007, 11:33 AM #5 smithy666   diyAudio Member   Join Date: Mar 2001 Location: Sydney 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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