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
Also, any views on what size sealed enclosure works best with this driver?
Thanks
Smithy
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
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
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.
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.- Status
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