The important parts?

[sackamous 10+ year member]

50in^2 per side. Why two chambers?

Was thinking the devider would make a stiffer box. Would one chamber be fine with out a hole lot of bracing?

 

[Phoenix Risen 10+ year member]

you can always brace the box with 1" dowel rods.

 

[ciaonzo 5,000+ posts]

Definitely want to go with a common chamber on this one. Bracing is one thing, tuning is another.

 

[RAM_Designs 5,000+ posts]

Was thinking the devider would make a stiffer box. Would one chamber be fine with out a hole lot of bracing?

Yeah, using a common chamber is pretty...common. Bracing shouldn't be an issue and using a single port will save you on MDF and save you some box volume(if you're restricted on your dimensions).

 

[pro-rabbit 5,000+ posts]

I agree. Common chamber allows you to skemp on space a bit as well. You can do a slot port instead of pvc and just use to sheets of 3/4" MDF for that large of a box.

Subs forward with the port up is ideal in most ext cab trucks where the box is this large. Do the port on the drivers side firing up.

 

[sackamous 10+ year member]

Ok need a little clearing up here.

I know I need a box that is 7.5ft^3 after sub displacement tuned to 32htz. I run that through this formula LV= [(1.463 x 10^7 x R^2) / (Fb^2 x Vb)] - 1.463xR with a 100in^2 port and get a lenght of 26 and 13/16. That means my port will take up roughley 1.55ft^3 not counting the wood. That leaves me around 5.95ft^3 after takeing out the port. Do I just increase the box size to get back to the 7.5ft^3 (would this mess up the tune?) or to I need to start with a bigger box size before I do the port calculation to end up with the right volume and tune afterwords?

 

[RAM_Designs 5,000+ posts]

You need to start with a bigger box size. Figure out how much total air space your port is going to take up, and account for your subs and bracing as well. Then add that figure to the volume you used to find your port length, and you have the total volume that you need. Next, just plug and chug on some calcs to find what dimensions will work well for you. I normally go a little larger with easy dimensions(like solid inches, no fractions) and throw some 45's in the corners to take up the extra room.

 

[sackamous 10+ year member]

Ok so to make sure I got it right, I know 7.5 is the net I need the subs to see. Use that for the formula for port lenght. Then I just need to account for the port volume, subs and bracing in the box. So I just need to figure my box so the subs see the net of 7.5 and my tune will be correct no matter the total volume of the box?

 

[sackamous 10+ year member]

Oh if I end up with a turn in the port how do u measure for that? On the inside corner or the outside or split the difference?

 

[speakerdude123 10+ year member]

So I have a question about calculating port length, what volume do you use when calculating?

Do you use the total volume including port and displacement. Or do you use the actual volume that is available (subtracting the port and displacement)

 

[RAM_Designs 5,000+ posts]

You use the volume that you're wanting to have after all displacements, ie: what the subs will actually see.

 

[RAM_Designs 5,000+ posts]

Oh if I end up with a turn in the port how do u measure for that? On the inside corner or the outside or split the difference?

Travel down the middle of the port.

 

[speakerdude123 10+ year member]

You use the volume that you're wanting to have after all displacements, ie: what the subs will actually see.

So say you have a box with 2.5cubes and after displacement it is 2cubes, you would use the 2cubes for your calcs in the port length, correct.

 

[RAM_Designs 5,000+ posts]

So say you have a box with 2.5cubes and after displacement it is 2cubes, you would use the 2cubes for your calcs in the port length, correct.

Right. Post #22 is the best way I can explain it, and the easiest way for me to do it.

 

[sackamous 10+ year member]

ok this is what I have so far

the outside is 41.5 x 23 x 20 5/8. The port is 26 13/16 long down the center u can prob still see the measure marks, its 2.5*40 so 100in^2. If i done the numbers right it should be 7.5ft^3 net after the port and sub displacement tuned to 32htz. This look right?