Box too big for ported 12" P3's?

[Towlieee]

So rockford recommends a ported box size of 1.79cf3, I thought it was a hair small, and went for 2.5cf3 at 35hz with 33sq inches of port.. The box isn't finished yet, so wondering if I should make modifications to drop it down to 2 or 2.25cf3 before finishing it?

1.79 seems small to me.... The 12" P3's will be getting 500w rms a piece, 4 of them in separate chambers, subs aiming up, ports aiming back along the bottom in an escalade.


Mock up picture

[DLHgn]

So each one will have 2.5 ft3 and ~33 inch2 port area? Why not running all of them in the same chamber?

[Towlieee]

So each one will have 2.5 ft3 and ~33 inch2 port area? Why not running all of them in the same chamber?

I was considering doing it that way, but its for a friend and he's using 2 different amps on them. Not ideal I know, but at least I gave the all their own chamber, plus it's just extra bracing. And yeah, 2.5 after port and sub displacement per chamber, 33"port area per chamber

I just feel rockford is being conservative in their box size to sell more to general public "hey it needs a small box", plus since we are only gonna throw around 500w rms at each one I figured a bigger box couldn't hurt and maybe give it a little more low end extension. He was impressed with my RE audio SE 15" in 3.7 @33hz on 600w rms, so I'm sure this will work for him. Just before I glue and screw the box together, if 2.5 is going to hinder them noticeably, now's the time I can still change it easy!

edit: oh yeah and my bad, I actually was going to finish it out with 38.5 sq in port area using 3.5"x11" slots for roughly 15 inches of port area per cube

[DLHgn]

So each one will have 2.5 ft3 and ~33 inch2 port area? Why not running all of them in the same chamber?

I was considering doing it that way, but its for a friend and he's using 2 different amps on them. Not ideal I know, but at least I gave the all their own chamber, plus it's just extra bracing. And yeah, 2.5 after port and sub displacement per chamber, 33"port area per chamber

I just feel rockford is being conservative in their box size to sell more to general public "hey it needs a small box", plus since we are only gonna throw around 500w rms at each one I figured a bigger box couldn't hurt and maybe give it a little more low end extension. He was impressed with my RE audio SE 15" in 3.7 @33hz on 600w rms, so I'm sure this will work for him. Just before I glue and screw the box together, if 2.5 is going to hinder them noticeably, now's the time I can still change it easy!

edit: oh yeah and my bad, I actually was going to finish it out with 38.5 sq in port area using 3.5"x11" slots for roughly 15 inches of port area per cube

Every driver is different and will want more or less space. I know my 12" does just fine in 2.5 ft^3 but it's also tuned to 26Hz and is for Home Theater. Plus it's a completely different sub. So just because mine work doesn't mean yours will. As for the bigger box means more low end extension, I don't think it does (could definitely be wrong) but I do know that it will give you more output at the tuning frequency but I believe it will in be sacrifice for cone control at higher powers. For the port area, your main goal is to make it big enough to reduce port noise and to not have port compression. The whole in^2 per ft^3 rule isn't that great and assumes way too many things for it to be accurate. Your best bet for all of your questions would to put your box, driver and power specs into a program such as WinIsd (it's free) and graph it. That will give you an idea of how it will all act (just keep in mind that the cabin of a vehicle boosts low end frequencies).

[Jessica]

My concern is with the driver orientation. they will all move different because they will be either closer or further from the port openings

Edit: punctuation

[ShadeTreeMechanic]

The reason people use a common chamber for multiple subs is so that the port will take up less room. Two different amps of the same kind right?

[DLHgn]

My concern is with the driver orientation. they will all move different because they will be either closer or further from the port openings

Edit: punctuation

If they're all symmetrical it shouldn't matter though

[ShadeTreeMechanic]

If they were symmetrical then two ports would need to go forward.

[DLHgn]

What do you mean? Aren't the drivers and ports on the same face?

[ShadeTreeMechanic]

Drivers up ports back. Some drivers are to the front some to the back. Having the ports in the back will put the port opening inside the box in the front. Some drivers will be closer to the port opening.