Compact subwoofer box for Peerless SLS-P830946

Hello everyone,
I've been trying to design for the first time an enclosure for a subwoofer with a Peerless SLS-P830946 sw. I came up with a 12 L box (final shape not considered yet), with a port tuned for 30 Hz. Made some calculations on WinISD and the result is a slot port of 30 cm2 cross area, 3 x 10 cm, about 78,6 cm long. I attached some graphs of spl, max spl and port air velocity. the slot port would be folded in the inside of the enclosure.
The whole project is for a car subwoofer that has acceptable extension and loudness and does not take too much space in the small trunk of my car.
Anybody can tell me if I should revisit something in the project or if there are better ways to achieve my goal?
Thanks in advance!


  • Max SPL.png
    Max SPL.png
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  • Port air velocity.png
    Port air velocity.png
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  • SPL.png
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  • Transfer function magnitude.png
    Transfer function magnitude.png
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WinISD doesn't give the correct dimensions of a slot port, because the end-correction is wrong for a slot port.
I switched to using VituixCAD because I can insert the 2.227 end-correction figure in it's port length calculations, because I want to use a slot port too.
A slot port with the right end correction will be shorter than a tube port of the same area.
There are many discussions about this here on the forum, so it's well worth a search.
I tried making a similar design on VituixCAD and as a result the woofer, which does not ever go super loud in its max spl, gets to 99.4 db at 30 Hz with a 30 cm2 cross area slot port, 60 cm long. I suppose the port flanges change the behaviour of the whole system as well, but i'm still not sure how big the impact is in general. I don't really expect much from such an enclosure though, just need a fine subwoofer to fill my car in the end.
Finally is there any way to roughly predict how much stuffing the box inside changes the total spl of the system? Should I put a lot of stuffing in it or too much can have a negative impact as well?