Okay, I need to know if I designed this ported box right...

[SomeGuyDude 10+ year member]

It's been a while since I've done it, but here we go. My aim for the RE SEX15 was 4.0cu with a port at around 34Hz. Got 'em from the RE site

So here's what I did:

I took optimal dimensions as 16.5" tall and 30" wide. These are INTERNAL dimensions, judging by the numbers in the later steps, hence 16.5" so I can get it 18" tall total. Then a 16.5x3" port, which means a length of 21.15" according to WinISD.

From there it's adding up the displacement (17.25x3x29.19 for the port) 0.633 + 4 + 0.17 for the sub = 4.80cu, yes?

Now it's that fancy-dan formula for my mystery dimension: depth. Take our above numbers and slam them together (4.80*1728)/(16.5*30) = 16.75

So my internal numbers are LxWxH of 16.75x30x16.5 internal, and 18.25x31.5x18 external, correct?

Now, figuring out the dimensions of the WOOD will require a whole lot of sketching, but I think I can do that just fine. I just need to make sure I've got all my digits correct.

My final question: how does one factor in a bending vent? If it has to be 21" long and I've got an 18" deep box, that's an extra three inches. Do I just take the 21" piece of wood that would normally go straight, then just cut it and re-glue/screw it where it would need to be? Seems to me that would affect its effective length, but maybe not.

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[dappa5 10+ year member]

if you need to turn the port you must measure down the center of the port

this will affect you overall volume due to the ports displacement

if you want a net (after all displacements) 4.0 ft^3 you will need to re figure your overall dimentions a 3 " port 21 inches long would make your internal volume 4.02 ft^3

that's before sub so add a little depth and you'll get the volume you want

 

[dappa5 10+ year member]

if you increase the overall depth to 19.5 " you'll get 4.45 after port b-4 sub that's with a three inch prt idk if that port length is even valid just going off what you provided

hope this helped next time just post max dims and ask for suggestions plenty of ppl here will add their $0.02

 

[SomeGuyDude 10+ year member]

Well I used WinISD for the port length. Punched in a 16.5x3 port in a 4cu box tuned to 34 and it told me 21.15" long. That's really all I know. I'm using the formulae from the EDU sticky.

EDIT: did all that wrong, re-sketching.

 

[GearGuy2001 10+ year member]

To bend the port since its longer then the depth of your box run your first wall back until you reach the width of your port as a distance from the back wall

IE 3" wide port then cut Internal Port Wall to 12.25" if 16.75" is your total OD dimensions

16.75" - .75" for back wall and .75" for front wall and 3" for port width= 12.25"

This picture might give you a better idea of how to "stack" the wood...

 

[SomeGuyDude 10+ year member]

That's what I was thinking. Looks like I'd need a 13" piece front to back and then a 3.5" piece at the back end for 21" total of length. It'd give me an effective front length at 16" and then 5" at the side. The only issue I see is that the less wood means a SLIGHTLY larger box thanks to less displacement. But nothing serious, right?

 

[GearGuy2001 10+ year member]

If you were doing a double baffle front thats 1.5 + 13 + .75 (width of wall 1) + 3.5 = 18.75

Youll have to tell me more about the box for me to help (double or single baffle front) Width of Port and Total Length(OD) of the box.

 

[SomeGuyDude 10+ year member]

The way it looks now:

Box DepthxWidthxHeight: 16.75x30x16.5 (internal), 18.25x31.5x18 (external)

Port: 16.5x3x21 (obviously internal dimensions)

Single piece of wood for the baffle

The top and bottom would be full size, left side full size, the baffle piece would be on top of the port piece and the right side like the image you gave. The numbers I've got so far with that would be like this, assuming .75" thick MDF (forgive the crudity):

 

[GearGuy2001 10+ year member]

The way it looks now:
Box DepthxWidthxHeight: 16.75x30x16.5 (internal), 18.25x31.5x18 (external)

Port: 16.5x3x21 (obviously internal dimensions)

Single piece of wood for the baffle

The top and bottom would be full size, left side full size, the baffle piece would be on top of the port piece and the right side like the image you gave. The numbers I've got so far with that would be like this, assuming .75" thick MDF (forgive the crudity):

With that pic you have 18" of Port Length, if you need 21 then you need to make the 2nd port wall 3" longer.

 

[SomeGuyDude 10+ year member]

Okay, I'm not doubting you, I just need to get an understanding of why that is.

I was under the impression that a bent port length is calculated by going down the center of the vent. So that means you'd start at the front and go down 16" (the center of that corner being 1.5" from each side) and then another 5" to the right from there, meaning a 1.5" gap before you hit the wood, then .75" for the wood thickness, then 2.75" for the remaining five. Like this:

What's the right way to calculate vent length when it has to turn a corner? The 18" is just the length of the inner wall of wood. And if it's as simple as that, life just got a LOT easier.

 

[csu87 10+ year member]

Okay, I'm not doubting you, I just need to get an understanding of why that is.
I was under the impression that a bent port length is calculated by going down the center of the vent. So that means you'd start at the front and go down 16" (the center of that corner being 1.5" from each side) and then another 5" to the right from there, meaning a 1.5" gap before you hit the wood, then .75" for the wood thickness, then 2.75" for the remaining five. Like this:

What's the right way to calculate vent length when it has to turn a corner? The 18" is just the length of the inner wall of wood. And if it's as simple as that, life just got a LOT easier.

thats how i do it. hope its right:crap:

 

[GearGuy2001 10+ year member]

Okay, I'm not doubting you, I just need to get an understanding of why that is.
I was under the impression that a bent port length is calculated by going down the center of the vent. So that means you'd start at the front and go down 16" (the center of that corner being 1.5" from each side) and then another 5" to the right from there, meaning a 1.5" gap before you hit the wood, then .75" for the wood thickness, then 2.75" for the remaining five. Like this:

What's the right way to calculate vent length when it has to turn a corner? The 18" is just the length of the inner wall of wood. And if it's as simple as that, life just got a LOT easier.

Hrm I always thought it was measured on the inside wall, but I guess I could be wrong lol

I guess it does make more sense to measure down the center.

 

[SomeGuyDude 10+ year member]

Yeah I was kinda grappling with that myself, and it's about all I can figure. After all if you take a length of bendable tubing that's 20" long and you kink it, the outer side gets longer and the inner side gets shorter, but the center distance remains the same. Or here's another way of looking at it, with an inner wall (the red line) that stays two units long:

But since we added a curve, now the area of the path is 5sq instead of 4sq. But again, I'm just a guy with a calculator, if anyone with more experience wants to correct me, please do.

 

[SomeGuyDude 10+ year member]

thats how i do it. hope its right:crap:

LOL yeah it's kind of an important thing since it can create a massive alteration in the tuning of the sub. I mean three inches off the port length can be the difference between a 34Hz box and about 36Hz, which could potentially be enough to throw the whole project off.

 

[atlninja82 10+ year member]

im pretty sure your port length would be 13.75 + .75 + 2.75 + .75 + 3. which would make it 21