Appropriate port dia for 15L box

[andy2]

Would 2in. Or 2.65in in diameter be appropriate for a 15L enclosure?
For 43hz tuning, the 2in. Port would be around 19cm in length and 2.65in would be 23cm. Does it sound right?

[PeteMcK]

The size of the box doesn't matter, except that it's a matter of being able to fit the desired port inside the box. The purists will howl, but I use ~ 2" for most ports, unless you're listening at extreme volume levels, port turbulence won't be an issue.

[sreten]

Hi, 2" is around 18/19cm but 2.65" is way more than 23cm, near 33cm, rgds, sreten.

[speakerdoctor]

I just finished a project with a 15L box, 2 inch diam port tuned to about 42 hz. Port length worked out to be about 23 cm. (i.e. 9").

[andy2]

I've read from somewhere that the actual port length will be about .7 of what you calculated from the equation.
So .7 (33) = about 23 is what I got for 2.65in. dia.

[Loren42]

Originally Posted by andy2

Would 2in. Or 2.65in in diameter be appropriate for a 15L enclosure?
For 43hz tuning, the 2in. Port would be around 19cm in length and 2.65in would be 23cm. Does it sound right?

It's more complex than that. You really need to know the T/S parameters for the intended driver, enclosure's true volume, and desired box tuning frequency.

The port diameter is a balance between vent velocity and pipe organ effects. The overall port length is another factor.

You want the vent velocity low enough to prevent port chuffing. However, port pipe organ resonance is also a function of port diameter and length. The effect will create a bump in the frequency response somewhere up the line. The larger the port area, the larger that bump can be.

If you are building a sub, having a very large port area is not so much a problem because the port pipe's resonance point will typically be above the sub's cutoff frequency.

[andy2]

Originally Posted by Loren42

It's more complex than that. You really need to know the T/S parameters for the intended driver, enclosure's true volume, and desired box tuning frequency.

The port diameter is a balance between vent velocity and pipe organ effects. The overall port length is another factor.

You want the vent velocity low enough to prevent port chuffing. However, port pipe organ resonance is also a function of port diameter and length. The effect will create a bump in the frequency response somewhere up the line. The larger the port area, the larger that bump can be.

If you are building a sub, having a very large port area is not so much a problem because the port pipe's resonance point will typically be above the sub's cutoff frequency.

So having two smaller ports instead of a large one will reduce the "bump"?

[Loren42]

Originally Posted by andy2

So having two smaller ports instead of a large one will reduce the "bump"?

If the sum of the port area is the same for both examples (single port versus two ports), the bump will actually get worse with two ports. This assumes the tuned frequency is also the same.

Vance Dickason's Loudspeaker Design Cookbook has good information about this effect and other effects with ports.