Port length and area help please

[swift 501]

I have a question regarding port length and how to measure it in my application. I have decided on one 15in FI-Q in a downfiring ported console encloser for my truck.

Question is:

I have attached a photo of an example I did and I don't know how to figure the length. And also, how do I figure the port area and will this be enough for a 15in FI Q. A SA-1500v.2 will power the sub.

The port will be 3.5in wide and 14.5 in tall (inside diameter) but how long will it be? Looking to tune at roughly 30hz and the box will have 3.65cu after displacement if this works.

Is it A, B or C. Red would be airflow

Thanks in advance

Edited December 14, 2010 by swift

[altoncustomtech 773]

From my experience, "A" will be the proper length dimension, due to the fact the air must travel around a bend equal to the rest of the port width it adds to the total length. Or, at least that's how I've been doing and figuring them for years, but I could have been wrong all this time.

[nick_19 1]

Option A would actually be 34.5 inches (don't forget to add .75 for thickness of wood). IMO, the best option would be to put a 45* angle in the corner of that port to make the width more consistent and call the length 33.475 inches (Option C plus the hypotenuse of the isosceles triangle formed by the 1.75" legs plus the .75 thickness of the port wall). That's how I measure with ports like that, personally.

Port area is simple: width x height. In your case, this is 50.75 in^2

Give me total outer dimensions and I'll give you your tuning and volume.

Edited December 14, 2010 by nick_19

[TooLoud4You 0]

Option A would actually be 34.5 inches (don't forget to add .75 for thickness of wood). IMO, the best option would be to put a 45* angle in the corner of that port to make the width more consistent and call the length 33.475 inches (Option C plus the hypotenuse of the isosceles triangle formed by the 1.75" legs plus the .75 thickness of the port wall). That's how I measure with ports like that, personally.

Port area is simple: width x height. In your case, this is 50.75 in^2

Give me total outer dimensions and I'll give you your tuning and volume.

I've always wondered how you figure all that out. Is there a formula you use. I know how to calculate the volume but how do you figure out the tuning. Any input would be greatly appreciated. thanks

[nick_19 1]

Option A would actually be 34.5 inches (don't forget to add .75 for thickness of wood). IMO, the best option would be to put a 45* angle in the corner of that port to make the width more consistent and call the length 33.475 inches (Option C plus the hypotenuse of the isosceles triangle formed by the 1.75" legs plus the .75 thickness of the port wall). That's how I measure with ports like that, personally.

Port area is simple: width x height. In your case, this is 50.75 in^2

Give me total outer dimensions and I'll give you your tuning and volume.

I've always wondered how you figure all that out. Is there a formula you use. I know how to calculate the volume but how do you figure out the tuning. Any input would be greatly appreciated. thanks

It's a forumla. The most popular source for it is JL Audio's website. However, I do not want to support JL Audio by giving their website hits. PM me your email address and I'll send you handy little Excel worksheet to aid you in your box building.

[swift 501]

Option A would actually be 34.5 inches (don't forget to add .75 for thickness of wood). IMO, the best option would be to put a 45* angle in the corner of that port to make the width more consistent and call the length 33.475 inches (Option C plus the hypotenuse of the isosceles triangle formed by the 1.75" legs plus the .75 thickness of the port wall). That's how I measure with ports like that, personally.

Port area is simple: width x height. In your case, this is 50.75 in^2

Give me total outer dimensions and I'll give you your tuning and volume.

Thanks, that looks like the only thing I forgot. 34.5 is correct. This looks like it will bring my tuning down to 28hz if the port is only 12.5 tall x 3.5 wide and would be 43.75 of port area based on 3.65 cubes internal volume.

Will this be enough port area for this sub and the box size? I could try and give you measurements but its a goofy size and may be better to post another pic of what it actually looks like.

[nick_19 1]

That's enough port area. 28 Hz is on the bottom end of the spectrum but will give you great low bass and a pretty flat curve (I prefer tuning in this area personally). Those specs look good as far as I can tell!

[Duran 387]

Enclosure size does not dictate port area

[nick_19 1]

Enclosure size does not dictate port area

Awww you know he meant volume

[Duran 387]

Enclosure size does not dictate port area

Awww you know he meant volume

Even enclosure volume.

[nick_19 1]

Enclosure size does not dictate port area

Awww you know he meant volume

Even enclosure volume.

Really? I've always been under the impression that, generally, you'd want more port area for a higher volume box... So they aren't related in any way?

[Duran 387]

Enclosure size does not dictate port area

Awww you know he meant volume

Even enclosure volume.

Really? I've always been under the impression that, generally, you'd want more port area for a higher volume box... So they aren't related in any way?

Depends on the woofers in said enclosure, high throw woofers will require more port area to stay linear, the opposite for say a pro audio woofer with maybe 5 mm of throw.

[swift 501]

I thought I kept seeing people recommend 12sqin of port per cuft of internal volume or something along those lines. This box will be a bitch to build and just want to do it right the first time. lol

Edited December 14, 2010 by swift

[swift 501]

well the Q says 28mm xmax and the port calculators say minimum 80in of port and I know I cant do that with a slot.... hmmm wtf do I do here?

[nick_19 1]

Screw a port calculator. Go with what Fi recommends on their website: 12-16 in^2 of port per cubic foot. Your good man. I always have around 12 in^2 port area per cubic foot and haven't had problems.

Edited December 14, 2010 by nick_19

[Kanaworm$ 292]

Try this http://www.psp-inc.com/tools.html

What is your max width, height and depth?

[swift 501]

Here are the actual build graphs I created (crappy I know) just trying to figure it all out. Center console between the back bucket seats with the port running behind the driver side back seat. This is in my 07 F250 Harley

Sorry for the bad photos

Top View

Side view port side

I may 45 the corners but other than that how does this look?

Setup will be a

Alpine Multi Media head unit

Alpine PDX 150.4 running 4 Alpine Type-R 5x7 coaxials in doors and 2 1in Rockford dome tweeters on pillars

Sundown 1500v.2 running the FI-Q 15

[swift 501]

If I do away with a slot port all together and do two 4in round ports and if I make them both going inside roughly 9.75-10in and the rest external I would have exactly 4 cubes and I could tune it to 28-32hz depending on how far the come out externally behind the seat. I would be hard to flare both sides though.

How would this effect sound quality and would you rather have 4cu and aero's or 3.65cu and a slot port?