Looking to build a box this weekend for a Death Row 18", 6.5 cuft, 90 inches of port area. Going to be a slot port, was wondering if it should be a 3" or 4" tall slot? Worried about wind noise (port noise) and tuning freq changing if the port is too narrow. Any advice? Should it really be bigger than 4" tall slot?

Thanks!

90 inches of port area means you have to make the AREA = 90, so the formula for area is L x W. just pick some numbers to equal 90 sq in

so 90 / 4 = 22.5

Worried about the noise made by the air moving, I have a 15" box with a skinny slot port and it makes alot of port noise.... it's like a 2" slot...

one more question. If I use 90 inch port area, with a 4" slot that would be 22.5" wide.

So port = 4" x 22.5" x ???

The length evades me.... I tried some port calculator scripts on a couple popular websites and I got 2 different results.

one says 6.5 cuft tuned to 32 hz with a 4 x 22.5 port would need to be 28" long, the other says 17.36" long? WTF? Anyone help me understand that? Seems like a huge difference to me and I thought all those port length calculator online thingies used the same or similar forumulas so I am really confused now...

I got it at about 28" long. Looks like your following the recommendations off of IA's site you should be all right then.

hey DB-R , we are playing with these too, it seems that alot of folks say they vary, also the end condition thingy weighs in on the math( wether you are shareing a enlosure wall with the port) the eqaution i copied down to find LV sems to be agreed on quite a bit, so i use the pencil paper and calculator method......

you are on the right track, well the same one i was on, perhaps the actual equation would be better for you also.

hey DB-R , we are playing with these too, it seems that alot of folks say they vary, also the end condition thingy weighs in on the math( wether you are shareing a enlosure wall with the port) the eqaution i copied down to find LV sems to be agreed on quite a bit, so i use the pencil paper and calculator method......

you are on the right track, well the same one i was on, perhaps the actual equation would be better for you also.

Where is this equation? Can you post me a link or post the equation? Thanks if you can! Forgive my ignorance, I do amps, not sub boxes, but I have in the past, but all sealed, so i am still "new" to vented boxes....

Where is this equation? Can you post me a link or post the equation? Thanks if you can! Forgive my ignorance, I do amps, not sub boxes, but I have in the past, but all sealed, so i am still "new" to vented boxes....

dB,

I would highly recommend reading over the JL Audio tutorials on Sub enclosures to get a really good foundation in box info. http://mobile.jlaudio.com/support_pages.php?page_id=141

Since you may already be familiar with some basic box designing stuff, you could probably simply go to the port tutorial section http://mobile.jlaudio.com/support_pages.php?page_id=165 and read up on the formula for finding the proper length.

After you familiarize yourself with the ported alignment math, you can then break into the various box mods that can increase SPL and all that good stuff. I may very well get flamed for referring you to the JL website, but I have always used the formula on their website for my box designs with a very high degree of success.

Brandon

hey DB-R , we are playing with these too, it seems that alot of folks say they vary, also the end condition thingy weighs in on the math( wether you are shareing a enlosure wall with the port) the eqaution i copied down to find LV sems to be agreed on quite a bit, so i use the pencil paper and calculator method......

you are on the right track, well the same one i was on, perhaps the actual equation would be better for you also.

dB,

Additionally, this gentleman is correct. If one wall of the enclosure is going to be part of the port then you must take end correction factor into account otherwise the tuning of your enclosure will not be correct. End Correction factor is found by adding half of the port height to the length calculation. In your particular scenario your port is 4 inches wide so half of 4 is 2. You would add 2 inches to the port length calculation which is 28 inches in this case for a total length of 30 inches. This should get you to a tuning of 32 Hz.

Box builders,

If I am wrong, please correct me so dB-r will know exactly what he is doing when designing his box.

dB-r,

One additional tip on box building is that you would ideally like to maintain a 8:1 ratio on the dimensions of your port. In your situation a 22.5 x 4 port will be just fine because that is roughly a 5.6:1 ratio on your dimensions. From what I've read and in my experience, violating the 8:1 ratio can definitely assist with port noise.

hey DB-R , we are playing with these too, it seems that alot of folks say they vary, also the end condition thingy weighs in on the math( wether you are shareing a enlosure wall with the port) the eqaution i copied down to find LV sems to be agreed on quite a bit, so i use the pencil paper and calculator method......

you are on the right track, well the same one i was on, perhaps the actual equation would be better for you also.

Where is this equation? Can you post me a link or post the equation? Thanks if you can! Forgive my ignorance, I do amps, not sub boxes, but I have in the past, but all sealed, so i am still "new" to vented boxes....

U CAN DO YOUR PORT AT 17.25 +5.25+19'' DEEP that should get u where u wanna be!

Looking to build a box this weekend for a Death Row 18", 6.5 cuft, 90 inches of port area. Going to be a slot port, was wondering if it should be a 3" or 4" tall slot? Worried about wind noise (port noise) and tuning freq changing if the port is too narrow. Any advice? Should it really be bigger than 4" tall slot?

Thanks!

what are the measurements you are working with?