Another Port Question...

[brewer_brewer]

12-16 square inches per foot is what i go by

[MAG-nanimous]

port area is calculated by (for a slot port) multiplying the height and the width (not the depth). the general rule of thumb is that you want 14 to 16sqin of port area PER cubic foot of box space.

the Port Area Range in the calculator already does some of the calculations for you and tells you what the optimum port area size is for the box you "made". and the Port Area is what you have inputted to the calc for the port size.

Thanks for that explanation. I noticed in the calculator the Port Area Range values would change after I entered a port dimension. Once those values change that's where I started to get lost.

Back to your suggestion, 2 x 10 x 20 would decrease my airpsace of 2.25 down to 1.7 but you said that the enclosure should still be fine even with the port? Would the tuning be altered a bit or would it still be close to around 35Hz?

The only reason I played with the short ports was because the calculator stated that's what the ports would be tuned at and I wanted to retain as much of the 2.25 as I could.

Thanks again.

[Guest]

Back to your suggestion, 2 x 10 x 20 would decrease my airpsace of 2.25 down to 1.7 but you said that the enclosure should still be fine even with the port? Would the tuning be altered a bit or would it still be close to around 35Hz?

The only reason I played with the short ports was because the calculator stated that's what the ports would be tuned at and I wanted to retain as much of the 2.25 as I could.

Thanks again.

thats why alot of people like to build bigger boxes to compensate for the loss of space from the port. having smaller ports can actually make the sub perform worse.

[Torres]

the reason why they change, is because as you're increasing port volume, you're decreasing the net volume of the box, which will slightly change the port range. it's not necessarily supposed to be relied on 100%, i just got tired of having to figure port area out every time i played around with a box design and was like hell...i can throw that on the calculator so i did. just as a guidance more or less.

if you do a slot port, which is what i'd suggest if you're trying to get lower tuning without sacrificing too much volume, then you can get a slightly lower tuning frequency with the end correction of the port. although...with the port volume, i dont think you'll be able to get anywhere above 2 cubic feet per chamber.

the best i can come up with is the same as krannymans box. tho i dont think i'd do it 2" x 20". that's a pretty thin port and could cause port noise. the general ratio is 1:6 or 1:7 (cant quite remember ) and that'd be 1:10. might work, but might not. 20 sq inches of port tho will suffice. and get you very close to your desired port tuning

oh 12-16 sq inches is also what i use for ports as well

[Torres]

thats why alot of people like to build bigger boxes to compensate for the loss of space from the port. having smaller ports can actually make the sub perform worse.

x2. i helped a guy from here design a box that he wanted tuned to ~28 hz. and in order to keep a decent volume, the port had to be very tiny. he build the box, and said it was better on only a couple songs and ended up putting his old box back in

[MAG-nanimous]

From what every one has been saying I have come to two conclusions about my build.

It's either ditch one of my 3 subs and just build the box for two which should give me the extra bit of airspace needed for the port to tune down to 35Hz or keep all 3 but set the port to tune at around 40Hz.

I read somewhere that usually 40Hz and above is what is used for spl competition and anything between 30 and 35Hz is best for daily use.

Can someone set me straight on this.

Thanks so far for everyone's responses.

EDIT: Exposport, I noticed on your calculator the tune frequency would change drastically just by flipping the value for height and width.

What I mean is, if I put 2 for height and 12 for width and then a certain length it will give me one frequency but if I put 12 on height and 2 on width the frequency will change. Is this correct? Thanks.

Edited May 20, 2009 by MAG-nanimous