Can I ballpark BIB parameters for driver of unknown T/S?

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I have acquired some pretty nifty 8ohm, 6.5 inch drivers that I would like to put in a big box/pipe/horn of some sort. The are from some old Olson bookshelf speakers and were running in there crossed with a 2uf cap to a tweeter (which crosses at ~4-5K right?). The drivers have pretty respectable alnico magnets and reverse roll cloth surrounds -- kinda like an enlarged FE103A. I think I've osmosed that BIB is fairly forgiving and also noticed that the measurements are fairly close for all of the 6.5" fostex drivers. Could I just work up something from those numbers and expect reasonable results? Is there a better enclosure for drivers of unknown T/S measurements?
Hmm, well you could build a BiB for a known driver, and then substitute your mystery driver in. And if it didn't work out, you could get the known driver for that BiB. BiB's are forgiving and I have put the "wrong" driver into them and was happy at the time, but I wasn't extracting maximum performance either.

A device to measure the drivers (woofer tester) is about $100. But if that's un-doable, you could use test tones to find the Fs -- that would at least be a start.
Thanks for pointing me in a direction. A) I had thought of T/S as all or nothing but it is easy enough to determine Fs so I'll get to that in the next while. B) I was unaware of the woofer tester. I might get one of those as I've got some other speakers I'd like to learn more about as well. Also a good idea to just build for a different 6.5 so I could put that one in at some point.


Joined 2003
Since I last opened this Excel SS, it got corrupted somehow, losing the basic drawing and scrambling up the calculation layout a bit, but the math is still correct.

Driver Diameter: 6.540 in
Desired Fb: 88.00 Hz

Sd: 33.593 in
Best Mouth Area: 268.742 in2
Best Width: 16.393 in
Best Depth: 17.268 in

Voigt Horn

height: 26.641 in
port height: 2.049 in
vent area: 268.742 in2
r-port: 9.249 in
nominal Vb: 4.355 ft3
123.318 L
L: 48.435 in
At: 2.049 in
Sm: 268.742 in2
X0: 0.4220 %
0.5780 % (corner)

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