Alright so my box is 5.38 cubes internally after the displacements besides the port. Im using a tube port thats 8'' diameter and I want to tune to 32Hz. My box only has about 20 inches of height to work with inside, so some of the port will be sticking out the top. I want at least 4 inches between the port and the bottom of the box. If anyone can help me calculate it out that'd be appreciated.

Why didn't you subtract the port volume from the box?

You know it is only 16" long. I will assume 1/4" diameter pipe. 8.5" total diameter by 16" is 907 cu inches or .52cuft. You have 4.85cuft. Around a 21.5" port should be close enough if my other assumptions were right.

Why didn't you subtract the port volume from the box?

You know it is only 16" long. I will assume 1/4" diameter pipe. 8.5" total diameter by 16" is 907 cu inches or .52cuft. You have 4.85cuft. Around a 21.5" port should be close enough if my other assumptions were right.

Its a sonotube cardboard type port im not sure on the material diameter but I dont think its 8.5''. I actally need 8'' clearance from the bottom of box to the bottom of port. I have 20.75'' height internally to work with and 22.50 if you could the .75'' of top peice of wood. I just need to know how much port I need to have in, and have out to have a freq. of 32hz. I've got 5.38 cubes with the sub in it sealed.

Umm, I answered. Don't post again without giving all the measurements you need.

And I bet the thickness of the sonotube is about a 1/4" anyways which would make the overall diameter 8.5".......

First you need to know the actual outside diameter of the tube.

If you have 20.75" internally & need 8" of clearance, then you can only have 12.75" of port inside the enclosure. Then the volume of the port inside the enclosure would be;

V = Pi * r^2 * h

Where r is the radius of the OD of the port and h is 12.75"

You would then subtract V from the 5.38cuft of enclosure volume you've already calculated, so you would have;

5.38 - V = net enclosure volume

You would then use the following formula to calculate how much total port length you would need;

Lv = (Av*1.84*10^8)/([Vb*(Fb/0.159)^2] - 0.823*sqrt(Av))

Where

Av = area of the port, Pi * r^2

Vb = net enclosure volume

Fb = desired tuning frequency

It's basic math, you can work out the calculations.

Thanks, I tried that formula but got stumped.

so far this is what ive come up with..

12.75'' in the box and that takes up .38 cubes. That leaves me with 5^3 internal volume. Based on the box calculator, I need 20.6'' port to have 32hz. So 20.6-12.7 = 7.85''

12.75'' in and 7.85'' out?

Edited December 23, 200915 yr by Bobby32