help designing Box for two Sa-8's at 30 Hz

[bbeljefe]

Circles are cut out. Im still a little confused. The smallest area i seem to be able to fit them in is 1'3'' x 1' 4 11/16''. Thats a little to wide. Rather have it taller. Is my port the right size and dimensions? Wish someone would just design me quick one.

Well then, it won't work I suppose. I didn't model the box for fitment but since you did, you have the answer. As for the port, it looks correct, although your measurements are hard to decipher, given that there are no visible indications of exactly which measurement applied to which portion of the box.

Perhaps that's not the case on your screen but it is on the photos you shared.

Oh and, on other idea (if feasible) would be to place the port at the bottom and load one driver in the front and one on the top. Or, vice versa, by adding a few inches of height to the side panels and getting the bottom face up off the floor a bit.

I wouldn't mind designing you one if I was a Sketchup guy but I'm not. I'm old and I use pen and paper to sketch my boxes and I don't make cut sheets, I just build.

EDIT: So basically, in the time it would take me to draw a box on Sketchup, I could build two of them, lol.

 

[Pyrofan]

Well then, it won't work I suppose. I didn't model the box for fitment but since you did, you have the answer. As for the port, it looks correct, although your measurements are hard to decipher, given that there are no visible indications of exactly which measurement applied to which portion of the box.
Perhaps that's not the case on your screen but it is on the photos you shared.

Oh and, on other idea (if feasible) would be to place the port at the bottom and load one driver in the front and one on the top. Or, vice versa, by adding a few inches of height to the side panels and getting the bottom face up off the floor a bit.

I wouldn't mind designing you one if I was a Sketchup guy but I'm not. I'm old and I use pen and paper to sketch my boxes and I don't make cut sheets, I just build.

EDIT: So basically, in the time it would take me to draw a box on Sketchup, I could build two of them, lol.

Well, im going to pen and paper now. Ill come back with the new revision.

 

[Pyrofan]

Ok, so i got a box that may work. I did the math i think its all right. The only problem is port speed. Its WAY to fast. like 160 ft/s. Does that mean this isnt gonna work? Its SHOULD be 1.3 ft^3

Pic of the box.

ImageShack® - Online Photo and Video Hosting

ImageShack® - Online Photo and Video Hosting

 

[bbeljefe]

Honestly, I've been building boxes since 1987 and I've never, ever wondered or worried about port speed. Port area, on the other hand, is important and it changes with the piston displacement of the driver(s). As for how fast the air moves through the port, that depends on the speed of sound and the amount of restriction the port provides.

Only thing that doesn't look right with that box is that it looks like the end of the port is too close to the side of the box. It really needs to be at least one full port length from the side wall.

 

[Pyrofan]

Honestly, I've been building boxes since 1987 and I've never, ever wondered or worried about port speed. Port area, on the other hand, is important and it changes with the piston displacement of the driver(s). As for how fast the air moves through the port, that depends on the speed of sound and the amount of restriction the port provides.
Only thing that doesn't look right with that box is that it looks like the end of the port is too close to the side of the box. It really needs to be at least one full port length from the side wall.

So if my port length is 26, then their needs to be 26in from the end of the port to the side. Is that even possible

 

[bbeljefe]

So if my port length is 26, then their needs to be 26in from the end of the port to the side. Is that even possible

No no... port width, not length. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif If your port is 1 5/16" or whatever we came up with, you need that amount or more between the end of the port and the side of the box.

 

[Pyrofan]

No no... port width, not length. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif If your port is 1 5/16" or whatever we came up with, you need that amount or more between the end of the port and the side of the box.

When i did the math myself, my width was 1.25. the distance from the end of port to wall is 1 in. Is that .25 gonna matter that much?

EDIT: So, i revised the box so that it wouldnt be closer then 1.25in. Its even. The box is about 1.46 ft^3. little on the big side but do yall think it will work?

 

[bbeljefe]

When i did the math myself, my width was 1.25. the distance from the end of port to wall is 1 in. Is that .25 gonna matter that much?
EDIT: So, i revised the box so that it wouldnt be closer then 1.25in. Its even. The box is about 1.46 ft^3. little on the big side but do yall think it will work?

Yes, it will make a big difference in that it would introduce turbulence and thus, noise. You're better off with higher tuning than noisy lower tuning. And if you mean the net volume is larger, that's too much of an increase for those subs. Your tuning will likely be lowered to the point that you have a nasty dip above Fb and too much peak at Fb.

 

[Pyrofan]

Yes, it will make a big difference in that it would introduce turbulence and thus, noise. You're better off with higher tuning than noisy lower tuning. And if you mean the net volume is larger, that's too much of an increase for those subs. Your tuning will likely be lowered to the point that you have a nasty dip above Fb and too much peak at Fb.

That 1.46 is after displacement. So great. i dont think the box can go any smaller. I did what the tutorials said.

 

[bbeljefe]

Not great. Here's the response curve for what you've drawn:

Remember me saying you'll have a nasty dip above tuning? That dip starts at 34Hz and goes almost -3dB throughout the entire bass range above it. And it falls off like a wall below tuning. Essentially, that's a 30Hz burp box with no acoustical gain.

Do what you want but again, those drivers do not do well in large boxes. One cube is about the max they're gonna be happy in and that's at 35Hz.

 

[Pyrofan]

Not great. Here's the response curve for what you've drawn:

Remember me saying you'll have a nasty dip above tuning? That dip starts at 34Hz and goes almost -3dB throughout the entire bass range above it. And it falls off like a wall below tuning. Essentially, that's a 30Hz burp box with no acoustical gain.

Do what you want but again, those drivers do not do well in large boxes. One cube is about the max they're gonna be happy in and that's at 35Hz.

Back to the drawing board! The biggest problem is port length. Some are want very long ports.

EDIT: im getting a port length of 33. Seems like that gonna be to long

 

[bbeljefe]

Back to the drawing board! The biggest problem is port length. Some are want very long ports.
EDIT: im getting a port length of 33. Seems like that gonna be to long

Again... one cube tuned at 35Hz. Port length as stated previously (25" iirc) and ~16in² of port area. ;-)

 

[Pyrofan]

So, i got 1.05 net volume ( using Torres)

Port area- 18.13

port length-34.10

34.86 hz.

Please say this will work

http://img203.imageshack.us/img203/9744/q9fw.png

ImageShack - SketchUp 2013-10-07 10-39-47-89.bmp

 

[jdawg90 10+ year member]

I've been designing a box for my sa-8's myself. I've done a TON of searching.

That port area sounds small. What I have gathered on here is you want 15-18 inches PER SUB (I think it was buck that said that but I'm not 100%). With the small space requirements of these subs that results in a port length of around 50 inches giving each sub ~.6 cubes.... yea fun I know.

I thought that sounded like a lot so I mapped out the vent velocity in BBpro and the velocity was pretty close to the velocity of an sa-12 in the recommended box size with 14 inches of port a cubic foot (what I read they like).

 

[Pyrofan]

I've been designing a box for my sa-8's myself. I've done a TON of searching.
That port area sounds small. What I have gathered on here is you want 15-18 inches PER SUB (I think it was buck that said that but I'm not 100%). With the small space requirements of these subs that results in a port length of around 50 inches giving each sub ~.6 cubes.... yea fun I know.

I thought that sounded like a lot so I mapped out the vent velocity in BBpro and the velocity was pretty close to the velocity of an sa-12 in the recommended box size with 14 inches of port a cubic foot (what I read they like).

Yea. I talked to Buck also. My port is 41in long tuned to about 34-35hz. The box is about 1.5 cubes with is the smallest it can be in my layout. Finishing up my box today.