damping PVC vents

[paulspencer]

Do PVC vents need damping? I suspect this is so. I'm designing a very intert box with a 4" PVC vent, which will be quite long ~720mm. I'm concerned it could have a bit of a ring to it (as it does when not in a box).

* at what intervals should the PVC be supported?

* should damping be applied to the outside walls of the PVC as well? If so, what should I use?

* suggestions for alternative vent materials?

* any ideas for getting smooth bends? I'm concerned any edges in a typical water pipe bend may cause turbulence.

[GM]

I've never felt the need to damp them, but one this long needs to be supported at ~62% from the baffle. WRT smooth bends, look at a vent's typical BW vs their Vb, they aren't an issue as long as their cross sectional area is relatively constant, only the terminations if there's a need for reducing vent 'chuffing' due to being too small.

GM