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Discussion Starter #1
Hi all, newbie to the forum here.

I'm working on a couple of small 4th order bandpass enclosures for a couple of 12" subs for my car at the moment (size is quite a constraint) and I'm curious about how the box sizes affect the frequency response.

I used a 4th order bandpass enclosure calculator to give me a series of specs to make my enclosure from. The calculator gave me the following numbers:

Sealed box: 17.6 litres (0.62 ft^3)
Ported box: 11.9 litres (0.42 ft^3)
Tuning frequency: 46.8 Hz

Which gives me a 3db rolloff at 30Hz and 73Hz.

What I found interesting was that the calculator told me to make the sealed box larger than the ported box, which goes against what a fair few people on forums around the place have been saying.

Why would the calculator say this?

If I swapped the volumes around in the boxes such that:

Sealed box: 11.9 litres (0.42 ft^3)
Ported box: 17.6 litres (0.62 ft^3)

And then tuned accordingly how would the sound be affected?

I'm quite unclear about the physics of the movement of air in 4th order enclosures vs the volume of the boxes.

Any help would be appreciated,
Rob
 
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