Can port dimensions be too big?

[acura3.2tl 10+ year member]

I am going to do 2 18" Fi Q's in a ported enclosure that will be roughly 12ft3 after all displacements. I want to tune at 32hz. Now with the dimensions of my box I was thinking of doing a port that is 4 inches wide by 38" long by 28" deep. Is the 38" of the port too long? Would that affect the bass with a port that long?

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[FamousMassacre 10+ year member]

Talk to double07

 

[fasfocus00 5,000+ posts]

only way to tell if it's not gonna work in a case like this is to do it. I've done ports that run the entire width of the box and only 3-4" tall, some made port noise and others didn't. i don't remember the exact ratio but it's something like 9:1.

 

[acura3.2tl 10+ year member]

I pm'd double07 once and never got a reply.

 

[mlstrass 5,000+ posts]

Length determines tuning for the most part. 4x38 is a little over the golden ratio of 9:1 but you will probably be fine.

Q's are bottom end monsters so if that's your goal 32Hz will be fine, otherwise I'd tune a few cycles higher...

 

[acura3.2tl 10+ year member]

I meant the ports outside measurements would be 4" x 38" and then the 28" would be the length of the port inside the box.

 

[mlstrass 5,000+ posts]

Correct, so 4x38 is your port area. Normally you don't want to go over 9:1 ratio, so every inch of width would equal 9" of height at the max. You're only a fuzz over that.

If 28" is the correct length for 32Hz tuning you should be fine. Going to big on port area will make the box have less control over the subs. Q's don't need a lot of port area, around 12^2 per net cube works fine.

 

[vented 10+ year member]

32hz i think is the actual recommended tuning for that sub anyhow, furthermore mlstrass is correct, an over large port can cause the sub to bottom out and exert too much causing damage to the sub and the coils. That could make a sub go from 5 years to 5 months before destruction.

I had a w7 and though since it was such a big sub i needed a huge port (i was watching too many you tube videos) and made a HUGE port it was like 6x15 and it blew in 3 months... i felt like a bastard.

 

[ciaonzo 5,000+ posts]

Going to big on port area will make the box have less control over the subs.

Glad you said that, it's a lesson many need to learn. It happens mostly above the tuning frequency where the driver is getting more power than the suspension can handle and the enclosure is not providing much damping because of the gaping hole in it, lol. I say mostly above tuning because most are smart enough to run a subsonic filter.
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