When someone with box calculating skills gets a minute, can I get a hand. What I'm after is what tuning frequency would be best for my cabinets and drivers? They will be about 94 liters net accounting for the driver and bracing volume. These will be ported cabs. The woofer is a JBL LE14H-3.
The Thiele parameters I found were for the LE14H, but I think there close. Is there anything else needed to determine what frequency to use for tuning the ports?
FS 26
QTS .27
QMS 2.3
QES 0.3
VAS 147.2
EFF .89
PE 150
XMAX 8.38
RE 5.9
LE 1.3
SD .066
BL 22
MMS 139
FLUX 1.25
Any thoughts are appreciated.
The main thing that port tuning does is greatly increase the power handling, and output around the tuning frequency by minimizing the cone excursion. In good designs the box Q is/should be high, and the port output is in phase with the driver above Fb, and out of phase below Fb with high Qb. Thus the tuning frequency also sets the point where the response will fall off fast, reaching 24 dB/oct.
One way to get a handle on a driver or get an idea of the ball park is to keep in mind B4 and B6 alignments. To put that driver in a B4 alignment you'd have the box volume equal to Vas, and the port tuning equal to Fs. Qts would ideally be higher but it will go up if you have a crossover inductor in series with the woofer, or you can just allow some error and run some sims to see where it would be.
A B4 is 3dB down at Fb with the maximum output possible without peaking - the rolloff is monotonic.
A B6 alignment calls for a box volume that is half of Vas or about 74 l for this driver, Fb is also tuned to Fs, and there is 6 dB less output at Fb due to the smaller box making it 9 dB down at Fb. An electronic peaked high pass with 6 dB of peaking is then added to bring the response back to -3dB at Fb again with a maximally flat rolloff. The peaking filter can often be left off with very low tunings where room gain will be helping out.
You'd be somewhere in between a B4 and a B6 with the 94 liters if you were to tune to 26 Hz, you could add a boost filter if you found it was needed in your room.
Another way to view this is with regard to what type of music you want to target this for. The lowest note on a grand piano is 28 Hz, and this or a bit higher might be fine if you're not interested in pipe organ or home theater effects. You could go as low as 20 Hz as a compromise if you wanted to reach a bit lower than 28 and didn't mind the reduced output or were willing to use a boost filter.
You could try some different tunings just by altering the port length and experimentation is probably best to determine what is best for your requirements. I favor low tunings since they provide a more gradual rolloff and better bass extension.
