Vent Size for MTM

[ron]

I am building a pair of MTM speakers using two (2) Vifa P17WJ00-08 woofers wired in parallel in a 28.3 liter box. Since I want the -3db point to be around 45 hz, I figued that a 3" I.D. x 6" long vent would do it. My question is if I use a 2" I.D. vent, what would the length need to be for the same -3 db down point? Also,would the bass performance not be as good with a smaller diamter vent?

[mike_e]

> I am building a pair of MTM speakers using
> two (2) Vifa P17WJ00-08 woofers wired in
> parallel in a 28.3 liter box. Since I want
> the -3db point to be around 45 hz, I figued
> that a 3" I.D. x 6" long vent
> would do it. My question is if I use a
> 2" I.D. vent, what would the length
> need to be for the same -3 db down point?
> Also,would the bass performance not be as
> good with a smaller diamter vent?

using windisd and tring to get to 45hz -3db down is not going to happen, unless im doing something wrong. The best i could get it to was 50hz -3db. the 3in port vent length 7.97inchs. 1.5 cu.ft. box tuned to 35hz.

[kduggan]

> 3" port is a little small according to Bass Box Pro but should work. in a 1 Cuft box with a 3x8" port you will get to around 55 -3db. Plot looks fine with this config, up to about 60 watts, before you run out of excursion.
using windisd and tring to get to 45hz -3db
> down is not going to happen, unless im doing
> something wrong. The best i could get it to
> was 50hz -3db. the 3in port vent length
> 7.97inchs. 1.5 cu.ft. box tuned to 35hz.

[Chris Roemer]

> using windisd and tring to get to 45hz -3db

A 2"d x 2.18" port will tune your proposed box the same as a 3"d x 6" port, but WinISD ( <A HREF="http://www.linearteam.org">www.linearteam.org</A> ) says you can expect port velocities of Mach 0.23 (I think that's around 150+ mph). Not recommended. Go with the 3".

Do you use WinISD?