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Old 15th May 2005, 09:07 PM   #1
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Default 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 ?
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Old 15th May 2005, 10:01 PM   #2
Volenti is offline Volenti  Australia
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Check that bassbox is (or isn't) calculating with fill in the enclosure (use Classical style, the other programs may use something similar), also check if all are calculating to the same Q (.707 or whatever) that'll make a big change in calculated volumes.
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Old 16th May 2005, 12:08 AM   #3
Ron E is online now Ron E  United States
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Default Re: Discrepencies in predictions

Quote:
Originally posted by Madmike2
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

-------------------------------------

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
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Old 16th May 2005, 08:41 AM   #4
simon5 is offline simon5  Canada
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WinISD seems to follow the ideal box, because results are 88 liters for a Fb of 41.78 Hz.
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