Cant figure port for Sundown SA 8v3 in recommended .5-.75 @35Hz

[dturro]

Hello everyone, i have spent countless hours trying to figure this one out. This is my first vented enclosure built for car audio purposes, just done PA systems which is "easier to work with". I want to keep the recommended volume size for this sub .5-.75. The calculations i had made so far has been only for a .75 enclosure, i am using WinISD, but there is a problem, when i multiply enclosure volume .75 x port area in this case 16, i get 1.2" wide for my port with a 10" height, and 32" long. But this will give me a wind speed of 117 feet/s which is = to port noise, a lot, at least in theory. if i use 20'' of port area i get better results, 85 feet/s air speed but 40'' long port. Can i use 20 as port area?( I ask because theoretically this would let the Sub woofer with less control) it seems to be the only way i can avoid port noise in this tiny box. i am tired, and i don't know what else i can do. I will put 500-600 watts to the sub, each. any advise guys? i have been looking on the web for two days and nothing. Any help will be appreciated.

Keep in mind that i dont have much space to work with in my car, so if the box can me less than .75 even better.

[Triticum Agricolam]

First off, please let me correct a common misconception you have. Less port area does NOT give you more cone control. In fact, the opposite happens, if you don't have enough port area your cone excursion will increase.

OK, now onto your problem. Getting enough port area while keeping tuning where you want with these small boxes is almost always a challenge. 16 sq in with .74 cf of net volume is probably going to be a good compromise between getting enough port area and the port not being unreasonably long. Your port is still going to be pretty long, but shouldn't be much over 40".

If you make the box volume smaller you can shrink down the port area a bit. At .5 cubes net you can probably get away with 12 sq in of port area, but the port is not going to be any shorter (it will need to be a little longer in fact).

Here's an example of a box I just did for an 8" sub. This will give you an idea of how much effort it takes to fit these ports in. Box specs are .7 cubes net, 12.75 sq in of port area and 32 Hz tuning. This box is only going to see around 400 watts, so I could get away with a bit less port area, this port is 39" long.

[dturro]

I think i posted this in the wrong section, i apologize, i will post in sundown section. Sorry

[dturro]

I think i posted this in the wrong section, i apologize, i will post in sundown section. Sorry

[dturro]

I think i posted this in the wrong section, i apologize, i will post in sundown section. Sorry

[dturro]

First off, please let me correct a common misconception you have. Less port area does NOT give you more cone control. In fact, the opposite happens, if you don't have enough port area your cone excursion will increase.

OK, now onto your problem. Getting enough port area while keeping tuning where you want with these small boxes is almost always a challenge. 16 sq in with .74 cf of net volume is probably going to be a good compromise between getting enough port area and the port not being unreasonably long. Your port is still going to be pretty long, but shouldn't be much over 40".

If you make the box volume smaller you can shrink down the port area a bit. At .5 cubes net you can probably get away with 12 sq in of port area, but the port is not going to be any shorter (it will need to be a little longer in fact).

Here's an example of a box I just did for an 8" sub. This will give you an idea of how much effort it takes to fit these ports in. Box specs are .7 cubes net, 12.75 sq in of port area and 32 Hz tuning. This box is only going to see around 400 watts, so I could get away with a bit less port area, this port is 39" long.

I apologize for the repeated replay, internet was down and i kept pressing the replay button haha. Thank you for your replay. Ok so getting more than 16 square inches of port area should actually be better and not bad like i thought, In this case then i can play a lot better with the port.

[dturro]

I did the calculations at .5 with 12 port area and i get way to much air speed, 68m/s at 20 inches long. If i do it with 30 port area, i get 63 inches long port 22m/s

[Triticum Agricolam]

I did the calculations at .5 with 12 port area and i get way to much air speed, 68m/s at 20 inches long. If i do it with 30 port area, i get 63 inches long port 22m/s

.5 cubes with 12 sq in of port area on 600 watts should be like 30 m/sec, not 68. 30 m/sec is still on the high end of things, but you could probably get away with it. What frequency are you tuning to?

You are never going to be able to fit a 30 sq in port in a .5 cube box. You really don't want the port getting much over 45" or so long. You will end up with a really poor working transmission line instead of a ported box.

[Joe X]

I did the calculations at .5 with 12 port area and i get way to much air speed, 68m/s at 20 inches long. If i do it with 30 port area, i get 63 inches long port 22m/s

SA-8v3 0.5net @33Hz 12 sqcm:

12 square inches of port area look just fine, check your model.

[dturro]

I did the calculations at .5 with 12 port area and i get way to much air speed, 68m/s at 20 inches long. If i do it with 30 port area, i get 63 inches long port 22m/s

.5 cubes with 12 sq in of port area on 600 watts should be like 30 m/sec, not 68. 30 m/sec is still on the high end of things, but you could probably get away with it. What frequency are you tuning to?

You are never going to be able to fit a 30 sq in port in a .5 cube box. You really don't want the port getting much over 45" or so long. You will end up with a really poor working transmission line instead of a ported box.

tuning at 35 hertz. Then i am probably using WinISD wrong if i am getting 68m/s @ .5 with 12. I have two subs, what if i put them both in the same chamber? that would give me better numbers and smaller overall than if i go individual chambers.