How important is minimum port diameter?

[downward_dog]

I'm modeling a box right now that calls for about a 3" (7.5cm) minimum port diameter. The only problem is that this makes the port about 12" (30cm) long, which won't fit easily within the box.

Would I be better off using a bent PVC pipe of 3" diameter (without flares), or a straight 2" port that is flared? What would be the problems with a 2" port - just port noise, or something else?

[Shaun]

It is always better to use a flared port to minimise chuffing (as a result of air turbulence). The other consideration is port compression at higher power levels. I suspect that these two are interrelated. Both of your proposals should work, but I'd still go for the flared port, even if it is to have a smaller diameter.

Most box calulation programs yield a minimum port diameter specification based on the assumption of a non-flared port. Flared ports often have to be a little longer (~1") to achieve the same tuning as a standard port. The tuning can be checked by doing an impedance sweep.