Question about Re-Tuning the 4430 Cabinets

[Zonker92]

I understand that the 4430 cabinet, with two ports that are about 4" in diameter and about 8" deep, is tuned to about 34 Hertz. I have also read that it is is desirable to re-tune the cabinet to about 29-30 Hz, by closing off one port and shortening the second port to about 4" in length.

I don't want to cut up my port tubes, and it looks like removing one of them (to replace it with a shorter one) might be a little destructive.

What if I just blocked one of the ports and left the other alone? I did see Zilch suggested that as a possible approach. What would that do to the tuning? I may just try it and see. Any other thoughts? Thanks.

(Disclaimer: OK, I admit it: I think they sound great as they are. I just like tweaking, but I don't want to damage the speakers in the process.)

(Confession: I also posted this question over on AK.)

[hjames]

Simplest thing is the so called "Zilch Plug" - go to Home Depot and get one of those Rubber pipe plugs that you tighten down with a wrench to expand and lock it into one of your ports. That gets half the job done pretty painlessly and is reversible. Only you can decide if you want to trim the other one.
You can see I've capped the right port on my L200 cabinet below.
I did paint the outer aluminum disc with black krylon before I installed it so you don't see silvery shine from behind the grill.

I understand that the 4430 cabinet, with two ports that are about 4" in diameter and about 8" deep, is tuned to about 34 Hertz. I have also read that it is is desirable to re-tune the cabinet to about 29-30 Hz, by closing off one port and shortening the second port to about 4" in length.

I don't want to cut up my port tubes, and it looks like removing one of them (to replace it with a shorter one) might be a little destructive.

What if I just blocked one of the ports and left the other alone? I did see Zilch suggested that as a possible approach. What would that do to the tuning? I may just try it and see. Any other thoughts? Thanks.

(Disclaimer: OK, I admit it: I think they sound great as they are. I just like tweaking, but I don't want to damage the speakers in the process.)

(Confession: I also posted this question over on AK.)

[Zonker92]

Thanks; I'm thinking about doing that.

In the sister thread over on AK, a kind member pointed me to a port calculator: It looks like plugging one port would tune the cabinet to around 25 Hz. Shortening the other port to 4.5 inches or so would bring it closer to 30 Hz.

[grumpy]

If temporary (I think you'd be hard pressed to tell the difference), buy four long bananas...
just don't forget them.

[Zonker92]

buy four long bananas... just don't forget them.

Haw. Bananas would be nasty.

I think you'd be hard pressed to tell the difference

Troo dat. Maybe I'll just try some cloth to see if I can tell.

[Jonis]

Proceed with caution on plugging one port as I think I've heard the pros here saying that if cabinet is tuned below the Fs of the driver it acts to unload the system at the lower tuned frequency possibly causing crazy excursions. I could have it wrong though.

[grumpy]

If you want to change the tuned frequency but not the bandwidth and efficiency of the port, you'll want to use something less absorptive than cloth. I was only half joking about the bananas. Sand filled paper towel tubes would do it.

[Zonker92]

Thanks to you both! I ran the calculator and it looks like reducing each port to about 3.2" would tune the cabinet to about 29 Hz. So I may figure out a way to try it.

And see if I would even notice ...

OK, I did the math (on-line circle area calculator) and it looks like a 4.1" port is about a 13.2 square inch circle. A 3.2" port is about 8.04" square inches. So to reduce the 4.1" port to 3.2" means losing about 5.16 square inches, which is about the size of a 2.6" inch tube. So Grumpy's idea is looking more and more suitable, but the tubes would be a little bigger than paper towel rolls.

[Lee in Montreal]

Be carefull. If you tune the cabinet to lower frequency, you will gain a bit of bass down low, but probably loose a lot of bass above this Fb.