Port Length

[Bobby32 0]

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.

[///M5 2,833]

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.

[Bobby32 0]

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.

[///M5 2,833]

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".......

[Impious 1,476]

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.

[Bobby32 0]

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, 2009 by Bobby32