Its allways risky with Helmholz Resonators. We had a lot of disskusiones and research and some works to, and we descoverd, that this formula is close.
http://mb.abovenet.de/allabout-hifi/...pic,112.0.html
This Formula should work
f = 172,71 * Wurzel(A/(V * (l + (0,732 * d))))
mit
f = Frequenz [Hz]
V = Volumen des Resonators [in liter]
l = Länge des Kanals in [in cm]
A = Fläche des Kanals ( = pi * r*r)
d = DURCHMESSER der Fläche des Kanals [in cm]
pi = 3.1416
Thanks to Joachim from kea audio for this
Gerd