Sub-30hz enclosure tuning questions.

[Buffalohed 10+ year member]

I'm just wondering how people do this, generally speaking. Whenever I use WinISD to try to model a sub with a low tuning for SQ, I get ridiculously long port lengths. And then when I raise the volume of the box to make the port shorter, the box ends up being way bigger than what the manufacturer recommends, for example a 15" Mag with a 5ft^3 box, just to get the port length under 40 inches.

How do you guys that have 15"+ subs ported at like 26-28hz do it? Do you just have an enormous box where the port wraps back and forth? Or do you significantly reduce the port size?

What are the disadvantages of having less than 60sq inches of port area per 15" sub, or less than 100ish for an 18? I guess I just don't see how enclosures with low tunings and large port areas are even remotely feasible.

I'm trying to figure out how a box for either 2x12" Mags or 2x15" Mags tuned to 28hz would work, just fyi.

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[helotaxi 5,000+ posts]

If the box is smaller you can go with less port area. A larger box will have a higher port velocity than a smaller one with the same port. The other thing you can do is flare the port. The increased area from the flare will increase the mass of air in the port lowering the tuning and the flare will difuse the air lowering the velocity of the air at the exit point of the port decreasing the likelihood of port noise.

The box I just built for my '03 XXX is 2 cf tuned to about 30hz. Port length of 45.75". Port goes down one side across the back of the box and then starts up the other side. 34.5 in^2 of port.

 

[THUMPPER 10+ year member]

it's hard to get away from a long port when building

a good low tunned enclosure...

building enclosures is like building an engine...

there is no replacement for dissplacement

make shure you brace the enclosure well

the excursion of those low notes flex an enclosure

like a balloon

 

[dvrmstrng 5,000+ posts]

my old box was 9.3 cubes tuned to 28htz...port you could stick your head in....its hard to do that with a small box ost: