Help with volume calculation

[andrew01]

Hopefully someone can help me with this calculation.

I have "re-used" two 12" drivers I salvaged out of a damaged sub enclosure which had an internal volume of 82 litres.It was
bass reflex with a port of 230mm long x 70mm I.D flared at one end. I have zero information about the drivers except they are marked as "P1208E" and impedance of 7ohms.

I have installed them in a new enclosure which meets the wife approval (inside / under the coffee table) but now has an internal volume of 88 litres.

Given that I don't know what the original tuning freq was , do I need to shorten or lengthen the port ?
If I leave it the same , will the tuning frequency now be higher or lower than it was ?

Thanks
Andrew

 

[kelticwizard]

Andrew:

Use the same port with peace of mind. Box volume differences under 10% essentially are negligible. Even over 10% are not bad. Your difference is about 7%.

Even if you removed 25% of your box volume, the only difference would be that you would be 6 dB down at the point where you used to be 3 dB down. A mere quarter of an octave difference. And that would be with 25% removed.

 

[pinkmouse]

You can usually get away with 10% difference in volume with no probs, so you can use the same port, but if needed, chuck a couple of bricks in there to reduce the volume. One brick is approx. 2l