What is the effect of foam on a tuned port?

[Geek]

G'day!

I have a two inch port that I wish dampened to keep the speaker from unloading at the bottom.

The plan is I have some 1/2" packing foam identical to the Y37ch found here:
http://www.foamorder.com/packing.html

As you can see, it's a medium density stuff that breathes pretty good.

Simple question - will this effectively lengthen or shorten the length of tube given me by calculators? Anyone have a ballpark percentage or formula?

Thanks

[GM]

Greets!

It does neither per se, though it does roff off the vent's output, ergo moves the cab's alignment towards a well damped sealed one. No simple rule-of-thumb I know of beyond ~2 lbs/ft^3 stuffing density using R-19 fiberglass insulation is the audible limit of change to my ears.

You can plug your design into MJK's PORTED WS and try different vent stuffing densities, though its sim is based solely on his research using polyfil.

GM

[Geek]

Many thanks for the info!

Technically, this experiment in a "happy medium" between bass reflex and sealed is for a full-ranger, so the complete results will be posted there when done.

The answer to this ties my last loose end.

Cheers!

[simon5]

This foam will simulate a bit the aperiodic box. I guess it will be closer to a ported box with the foam in the port.

http://www.partsexpress.com/pe/pshow...=296-546&DID=7