Discrepencies in predictions

HI all ..... why is it that i am getting completely different prediction models from Isdcad WINisd and Bassbox pro 6 for a closed box with the same two drivers. I am not talking about 5 or 6 % . I set them all for golden ratio but i get 2.2 cuFT for Bassbox pro, 5.5 + and change from Winisd and 3 cuFT + for ISDcad.

I checked all the parameters and they are all the same on each programs database of that driver. Hi-Vi D10G woofer, 2 in a closed box. Is there something hidden i am missing ?
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
Madmike2 said:
HI all ..... why is it that i am getting completely different prediction models ... with the same two drivers. I am not talking about 5 or 6 % . I set them all for golden ratio but i get 2.2 cuFT for Bassbox pro, 5.5 + and change from Winisd and 3 cuFT + for ISDcad.


Depending on what assumptions you go with, you could say that for the parameters:
Fs=25
Qts=0.44
Qes=0.54
Vas=138L

All of the results below are for Qtc=0.707, and all are justifiable results - except perhaps for the ideal box, that is ;)

Undamped ideal box
Vb=87Liters per woofer
Fc=F3=40.3Hz

Small Margolis undamped gamma=1 and Qa=10
Vb=69Liters per woofer
Fc=F3=43Hz

Small-Margolis damped gamma=1.2 Qa=5
Vb=46Liters per woofer
Fc=F3=46Hz

Benson formula (Like used in Bassbox 6+ and Unibox) lined, not stuffed, no adiabatic-isothermal assumption
Qa=20, Qp=0, Ql=20
Vb=71L per woofer
Fc=F3=43Hz

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The only way you can be certain of your model is to measure it after building a test box to see if the assumptions you used are correct. Interestingly enough, measurement at those frequencies can be difficult to interpret, and once you get out of the small-signal arena all bets are off anyway. Makes it seem amazing that anyones' boxes sound good, doesn't it? ;)

So build your boxes somewhere between 46 and 87liters per woofer and you should be happy ;)