Box Design

[Frostedflakejake 148]

So i've been working on box design for my new SA-15's.

For external dimensions i have: 32 wide x 20.5 tall x 24 deep for 7.55 cubic feet before port volume or displacement. Wood thickness is .75" Then for a port, i would have the dimensions 30.5" wide , 4" tall and then 18.16" deep. I got the port dimensions from CarStereo.com. According to that site, the box is tuned to 32hz. I was wondering if that was correct or not because i know tons of those sites end up being wrong with tuning. Here's a picture describing my plan. The lines in that picture are parallel... I don't know why the camera says differently. So does that sound alright? If not, can someone please correct my math/design? Thank you!

[Frostedflakejake 148]

Edited March 5, 2011 by Frostedflakejake

[NB50 206]

I'm getting more like 5.7ft^3 @ ~44hz after all displacements.

[Frostedflakejake 148]

Yeah Bromo i didn't trust that. So i used winIsd and now my interior dimensions are 31.5 x 19 x 22.5. Then i'm using four 3" diameter cylinder ports that are 7.16 inches in height. Does that sound more correct?

[RAM_Designs 25]

Use a pair of 6" aeroports(real ones) instead.

[Frostedflakejake 148]

What's the advantage?

[NB50 206]

Yeah Bromo i didn't trust that. So i used winIsd and now my interior dimensions are 31.5 x 19 x 22.5. Then i'm using four 3" diameter cylinder ports that are 7.16 inches in height. Does that sound more correct?

Yes, I got it at around 33hz. But your port area is really suffering.

[Frostedflakejake 148]

So how do i tell if i have adequate port area?

On a side note, if i up-size the size of the port to 6" inches would that be more beneficial? two 6" ports at 14.31" long? Is there any special material that should be used for the ports? I was just going to use PVC because i had lots of it with an ID of 3" but since I need larger ports and am going to have to buy something then I might as well make sure it's something suitable. But i would like it to be something i can get at my local Home Depot so aeroports are out of the question.

Thank-you both for your responses

[Frostedflakejake 148]

And i remember why i was worried about 6" ports before. The box will be 22.75" tall with the double baffle. I was worried about clearance from the bottom of the subs to the ports. I know that may sound silly, but would that be an issue?

[Frostedflakejake 148]

Okay. So I know the usual recommended spec is a 12 sq inches of port for every cubic feet of box space. I must be too tired because that seems absolutely impossible! 7.8 cubic feet * 12 sq inches of port is 93.6 inches of port area right? Well a 6 inch diameter pipe has a surface area of 9pi ~ 28.26 sq inches. So i would need three 6" ports (84.78 sq inches) of port plus a 4" port (12.56 sq inches) to get the right amount of port area?! Is that right or am i overlooking/underlooking something...

[RAM_Designs 25]

If doing a pair of 6" round ports, you need to use flared aeroports. They can be found at www.partsexpress.com. The whole 12-16in^2 of port per ft^3 doesn't apply to aeros because the flared ends make them less susceptible to port noise, so you're able to get away with less port area. I've used single 6" aeros on a lot of 15" subs and they work fine. If you want, you can use three, but you're going to have to get your own thin-wall PVC to make the ports long enough; the kit from psp allows for just 17" total length.

Edited March 7, 2011 by RAM_Designs

[Quentin Jarrell 671]

minimum port diameter by Richard Small, the guy where they got the "s" from in T/S parameters

dv=39.37(FB x VD)^.5

dv= diameter of port in inches

FB= enclosure tuning frequency

VD= volume displaced by woofer(incubic meters)

to calculate VD

VD= sd(in square meters) x xmax(peak to peak in meters)

[Frostedflakejake 148]

Okay that makes sense. If the ends aren't flared though, the same old rule still applies?

Here's the skinny, i have till Friday to make this box. I didn't account for port area because I was stupid and lazy and just let winIsd do the work for me. So what I'm left with now is a box with all sides on it except for my baffle. I was going to put ports in the front side of the box and I'm really glad I didn't do it tonight because the port area is horrible too small. The box has to be done by Friday because on Friday I go back to school (9 hours away from home). This is why I'm trying to figure out other methods than PSP ports. I'm afraid if I order ports, they won't be here in time. I really don't want to pay for faster shipping. I could get two 6'' ports to my door by Wednesday for around $80 as a last resort. But that sucks. Do you understand my dilemma? I would love to use some 6" piping of other material but without the flared edges I would need three 6" tubes all 25" long. That's 6' 3'' of tubing and probably wouldn't be all that cheaper than getting two 6" PSP ports.

A slot port wouldn't be impossible at this point. I'd just need to do careful cutting. However I don't know how to calculate slot ports

So is there anything I can do? I'd rather do the slot port at this point than bite the bullet and buy those PSP ports. But then I also run into the problem of the slotport volume being high enough to put my net volume of the box too small. Can someone calculate a slot port for me? Or more likely, tell me how to? I just don't trust any of those online sites. I've heard way too many that give wrong numbers. i did try using the formula for box tuning with cross sectional area and length of port, but i ended up needing a port about 1243 inches long... so i obviously screwed up somewhere. Help?

Edited March 7, 2011 by Frostedflakejake

[Frostedflakejake 148]

Thanks Audibel. However, I don't know and don't know where to find the SD spec or even xmax on the SA-15. The specifications list on sundown audio's website is blank

[Quentin Jarrell 671]

after calculating net volume after port and sub displacement, using 3 6" ports, you will end up with about 3 cubic feet per sub. Or 2 cubic feet per port. If you use that much port area each port will need to be about 33" long to tune to 32 hertz

[Frostedflakejake 148]

I appreciate that

Ha if only my box wasn't only 24" deep

It's looking like i'm going to have to go back to the slot port idea eh?

[Frostedflakejake 148]

Okay I have an idea. I hope these posts don't get annoying, but I'd rather try this myself then just have somebody give me measurements and then walk away not learning anything. What if I turn the front into a slot port? 4.5 " wide, 19 " tall, and then 17.43" into the box? I know the cross sectional area isn't as much as 12" per square foot, but if i kerf the side of the port that's inside of the box will I be able to get away with if? I was afraid that with the 5" wide port the port length would be so close to the back of the box. I got a port length that would have to be about 20" leaving only 2.5" from the end of the port to the back side of the box.

Thoughts? Feelings? Concerns?

[///M5 2,833]

Are you still using WinISD? What does the peak port velocity come out to with the power that you will be applying?

[Frostedflakejake 148]

Yes I've been using WinIsd for all calculations except for the improper first vent dimensions. That's why im so confused. I thought the "vent match" number on winIsd was a measurement of port velocity and if that number was low, port velocity would be low and then port noise would be low as well. Obviously I'm not fully understanding the concepts.

Now to your question, I'm not sure where to enter the power that I'll be using. I was under the impression that you enter the power you're using under the PE section in the T/S parameters. Is that correct (i have 600 in that slot right now)? And is peak port velocity the number in the "vent match" section? I thought it was since that measurement is in Mach. That must not be right though because on all the port options i've listed so far i've gotten good vent match numbers; all around .03