could someone calculate this tuning?

[DBBOOM 10+ year member]

I know the picture looks confusing but if you look at it you will see a double dimention line on the bottom indacating that he is not measuring from the bottom of the box but the bottom of the port opening.

Small screen, sorry. Maybe that is why hes getting such a varied number from the other guys also.

 

[Mike465 10+ year member]

Small screen, sorry. Maybe that is why hes getting such a varied number from the other guys also.

It's all good man, I forgot to add sub displacement so I came up with 3 numbers. Yeah, but if he wants it tuned to 38Hz he will have to increase the port lenght to 17.36 inches long

 

[tommyk90 5,000+ posts]

After a closer review I switched two of my dimensions in the port calculator. //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

Sorry about the mistake. Lemme whip something up here. (i'm the designer in case you haven't guessed)

 

[tommyk90 5,000+ posts]

Here, try this one instead. Sorry about the brainfart there.

This one actually drops the tuning down to 36 hz according to the online calculators, but I trust my measurements more. Besides, 2 hz is not going to be a noticeable difference, especially if you plan on playing music. And actually, that will benefit you anyways if you plan on adding some bracing to the inside. That will decrease the net volume which will effectively raise the tuning anyways.

 

[Lil Poot 5,000+ posts]

Here, try this one instead. Sorry about the brainfart there.
This one actually drops the tuning down to 36 hz according to the online calculators, but I trust my measurements more. Besides, 2 hz is not going to be a noticeable difference, especially if you plan on playing music. And actually, that will benefit you anyways if you plan on adding some bracing to the inside. That will decrease the net volume which will effectively raise the tuning anyways.

whats the volume after sub displacement of this one?

 

[Lil Poot 5,000+ posts]

better yet, could someone explain to me how to calculate the volume and port area of a box myself? getting the volume of a sealed box is simple, but i've never seen a writeup on how to do a ported box. do you subtract the volume the port takes up from the total volume of the box?

the port is calculated in area and not volume though right, i'm guessing just the surface area of the port wall itself front and back?

 

[Lil Poot 5,000+ posts]

lol nevermind... reading stickies ftw.

 

[Lil Poot 5,000+ posts]

ok so as far as i can tell, its right at 12 cubes net and tuned to 36 hz. wouldnt i be better off using a slightly shorter port, increasing the net volume and raising the tuning just a cunt hair?

the outer dimensions i like, i dont really want it any taller than that, or any deeper, (closer to the hatch) and 41.5 is as wide as i can go.

 

[Lil Poot 5,000+ posts]

another thing i noticed, is that dj recommended 16 sq inches of port per net cubic foot. with 12 cubes, that comes out to 192 sq inches, 4.8 inches tall, since i have to keep it 40 inches wide, would that even be a noticable difference in the final product?

 

[tommyk90 5,000+ posts]

whats the volume after sub displacement of this one?

Still 12 cubes.

The box has to be substantially larger because of the increased port length, and thus port displacement.

It's a hair over 15 cubes gross.

 

[tommyk90 5,000+ posts]

ok so as far as i can tell, its right at 12 cubes net and tuned to 36 hz. wouldnt i be better off using a slightly shorter port, increasing the net volume and raising the tuning just a cunt hair?
the outer dimensions i like, i dont really want it any taller than that, or any deeper, (closer to the hatch) and 41.5 is as wide as i can go.

When you decrease the port length, you effectively make the box larger.

If you cut the port length down 2" (making it 18" total), that will make the box 12.3 cubes and will make the tuning ~38 hz.

another thing i noticed, is that dj recommended 16 sq inches of port per net cubic foot. with 12 cubes, that comes out to 192 sq inches, 4.8 inches tall, since i have to keep it 40 inches wide, would that even be a noticable difference in the final product?

I would do a hair less port area because of the large enclosure size and tuning you are shooting for. You want to maintain some control over the sub excursion at high volume levels.

If I were to bump it up to say 4.75" with 20" of length, that gives me 11.9 cubes net and a tuning of roughly 38 hz again.

 

[defdaboss 10+ year member]

okay guys. my turn..

box dimension

31"L x 13-1/2"D x 13-1/2"H SEAL BOX

port circle

4" W x 4 1/2" D

what's my hz?

 

[tommyk90 5,000+ posts]

better yet, could someone explain to me how to calculate the volume and port area of a box myself? getting the volume of a sealed box is simple, but i've never seen a writeup on how to do a ported box. do you subtract the volume the port takes up from the total volume of the box?
the port is calculated in area and not volume though right, i'm guessing just the surface area of the port wall itself front and back?

Here is the way I do it if i'm using a pencil and paper.

1)Find out what net volume you want (dimensions you can work in as well)

2)Find out how much port area you need

3)Knowing the net volume desired, find out how long the port has to be

4)Calculate the port displacement. In the case of a slot port: height x (width+.75) x (length-.75). Add .75 to the width for the port wall, subtract .75 from the length because the port goes through one of the sides

5)Port displacement + sub displacement (and any bracing) + net volume=gross volume

6) Draw up a box that has the gross volume desired.

For instance, you want your box to be 12 cubes net. Say the port for that size enclosure will displace 1.5 cubes. Sub displacement is .5

So 12+1.5+.5=14 cubes.

So you want to draw up a box that is 14 cubes gross.

 

[Lil Poot 5,000+ posts]

cool, thanks for all your help.