Calculate box for basreflex

[weedo]

Look at the equations below.

Speaker:
fs = Resonant freq (Hz)
Vas = Equivalent volume (litres)
Qts = total Q value

Box:
Vb = box volume (litres)
fs = box resonance (Hz)
fu-3dB = -3 dB frequency (Hz)



I have used (so far) alt 1. But recently I found alt 2 for the box volume.

What alt is the "best"?

Does anyone have other equations for fb and fu?

[Ron E]

There is no best way to design a vented box. Alt 1 is from D.B Keele and is frequently used as a starting point or reality check. Another set of equations from Small-Margolis (JAES 1981) are:

Vb=20*Vas*Qts^3.3
Fb=Fs*.42*Qts^-0.96
F3=Fs*.26*Qts^-1.41

Your Alt 2 appears to lie somewhere between these two.
it simplifies to Vb=Vas*14*Qts^3

These simple equations are just curve fits of much more complex functions, but they actually work quite well.

If you want to delve deeper, get the loudspeaker design cookbook from Vance Dickason as a start. From there you must read journal articles, such as from the Journal of the Audio Engineering Society, although to understand much you should have some engineering education.

[Rademakers]

Next to that you can simulate with a program like WinISD Pro. It's freeware that visualizes the information in graphs like the frequency response, cone excursion, phase and the effect of filters, etc.
There are some guides on the web, on how to use it, like the one in the Wiki.

Wkr Johan