Hello.
According to the litterature, adding insulation (or mineral wood or fiberglass wool or stuffing or pillows or whatever you call it) inside a cabinet actually increases the effective volume of that cabinet.
Is there any way to calculate that? Any data?

By the simulations I made in WinISD, I built a 254l cabinet tuned to 27Hz with ports of 32cm.
After measuring, the cabinet actually has it's impedance dip at 24-25Hz which would suggest a volume of 321l with that port.

Question: Can the adding of "stuffing" increase the effective volume from 254l to 321l?
I don't feel like stripping clean the interior of the cab just to check, is it a good idea to assume my cab has now a volume of 321l and base my port calculation on that?

Thanks for any insight.