Ports & Tuning help needed

[Tom Loizeaux]

I have an 8 cu.ft. box that I want to mount a JBL 2241 or 2242 in. I want to use it for some low end (sub woofer) assist with a smallish PA.
JBL recommends a 10 cu.ft. box, tuned to 40Hz, requiring 6 4" tubes 5.5" long for either of these drivers.

1) What tuning freq. should I use?
2) How many 4" tubes and how long should they be to tune either of these drivers properly in my 8 cu.ft. cabinet?

I could build a box port instead of using 4" plastic tubes, so I guess I need a number for the cu. in. required in this cabinet.

Thanks in advance,

Tom

[GordonW]

I ran the numbers for a 2241H...

From what I saw, for 8 cubic feet, I'd line the top, bottom, sides and rear walls with a 4" thick layer of fiberglass insulation, and use either 5- 4" diameter ports, 10" long, OR a 7"x9" vent 10" long, OR a 13"x5" vent, 10 1/2" long. This will give a tuning frequency of about 37 Hz, which in that size box, is about as high as I'd go. Higher than that, you start to get significant peaking in the response, due to the box being smaller than originally spec'd.

According to my program, this'll give an f3 of about 38 Hz or so. Should be pretty potent slam. If you want more low bass, just use a longer port (about 12" long for the 4" ports or the 7"x9" vent or 12 1/2" for the 5" x13" vent) and add a little 1/3 octave EQ at 40 Hz or so. This should get you into the low-mid 30s for a rolloff point, which should most likely satisfy even most heavy-bass keygboard players and such...

Regards,
Gordon.