18" BTL box.... to small???

[animalbmx1 0]

I just finished building my box last night.... Double baffle,Fiberglass,etc... My box after bracing and before the Port was 8.25cuft(internal)I have 119 sqin of port tuned to 30hz. After the displacement of the port I now have 5.85cuft. Now is my box 8cuft tuned to 30hz OR is it 5.85cuft tuned to 30hz??? And would that be too small for an 18??

thanks

[BKOLFO4 29]

It is 5.85 ft^3, but you have another problem - If it was calculated to be tuned to 30 Hz based on 8 ft^3, it is now tuned much higher since it came out to be 5.85.

Post measurements so we can calculate what you have. You may have to block off part of the port. It will become part of the enclosure, and the smaller port will lower the tuning frequency. You only need 80-90 in^2 of port area.

You can tune as high as 34-35Hz and still have plenty of low end bass with a BTL 18. . . .

[animalbmx1 0]

Well my port is 5.5 inches wide and 21.5" tall and is 33 inches long.. Now I plugged those numbers in the on the port calculator on CA.com and according to that I am tuned to 35Hz with the 5.85cuft of volume. If that is true than I'm going to keep it as is and just see how it sounds.. BUT for future reference in what order do I figure the Port/box size out. I figured out the NET volume which was 8cuft than plugged the port size WxH and it gave me the length I needed to be at 30hz. I guess I have no idea how to design a box

[animalbmx1 0]

Doesn't the Useable airspace change as the size of the port changes???

[BKOLFO4 29]

5.85 include the driver displacement?

I would cut the port down to 80 inches, gain the extra box space, and it would lower the tuning frequency.

[Fi Car Audio 64]

Yes, as you increase port sizing or length you loose useable airspace in the enclosure. Rather quickly you hit diminishing returns and run into problems.

5.38 tuned to 35Hz isnt too bad. Since its done, Id run it and see how it goes. We can tweak things from there after break in and depending on what you want to change (if anything).

As BKOLO4 mentioned, you could simply cut the port down to 4X21.5 and shorten it to the correct length for tuning and the new net volume with less port displacement as well... but try it as is first if its not difficult to do so.

Thanks,

Scott

[animalbmx1 0]

Thanks for all the help.. I have some new measurements for another box let me know how this one sounds!!

14.75x24.5x46.5/1728= 9.7cuft(internal dimensions) after driver displacement that would make it 9.4cuft(internal)

Port would be 24.5x4.5 23.75" LONG That would bring my internal volume after PORT&SUB to 7.7cuft with 110sqin of port tuned around 30hz. Does that sound about right???

[///M5 2,833]

I didn't check the math but why on earth would you tune a BTL to 30hz??

[animalbmx1 0]

ahhhhh why wouldn't you???

[BKOLFO4 29]

32 is as low as I would go, and I am VERY happy with 35. . . and I have run MT's at 40!!!!

Brian

Edited November 28, 2007 by BKOLFO4