Now, I have a pair of old SEAS 13" woofers in good condition which i intend to use for a 3-way active design.

Now, I have a calculation program (CAAD 3, an old freeware application)

which I have been using just for playing around a little.

Now here's the issue; According to the calculations, the ideal box size is around 170 L, giving a -3dB of around 35 Hz.

In terms of low frequency, this is where I would be happy to end up, so that's OK.

I am however a bit puzzled about the cabinet size, as the original SEAS datasheet quotes: "closed box 50-100 L" and "Bass reflex 70-100 L"

170 L is obviously a lot more than the guidelines provided by SEAS.

I have tried tweaking around with the program, and for a vented box with a volume of 100 L, I can obtain a -3dB of 42 Hz. with a linear response.

Ok, but not great for a 13" driver with a Fs of 27 Hz....

My first assumption is that a 170 L box with a -3dB of 35 Hz is a theoretically extreme application of the driver not considered a "real world" application by SEAS.

My second thought is that the driver could well be capable of delivering very low frequency response in a 100 L vented box, but that the software I'm using is somehow not quite appropriate.

Any views and comments from those of you with practical experience with using box calculation software would be greatly appreciated.

Best regards,

http://www.seas.no/images/stories/vintage/pdfdataheet/h175_33fzbxdd.pdf