If I have two 12 inch subs and a 15 inch sub in a box,do I have to keep the air space for each separated

For optimal performance there is really only one size for the box .Firstly, you get two different types of subwoofers, an open air, or closed air sub. If it is an open air sub ( hole with mesh in the center of the magnet) no ports are required, and the box should be sealed on the inside with silicone sealant. If it is a closed air sub ( no hole in the magnet) you need a 50mm port about 120mm long. If it is a 12 inch speaker, the box size will be 13 inches x 13 inches x 13 inches.

The MTX Thunder 6000 T61544A is a 15" Subwoofer meaning you will need a 15" hole to fit the subwoofer into. The mounting plate that surrounds the subwoofer will extend past 15" allowing you to screw the sub in properly. Be sure to use a box that is at least 12 inches deep (sub is 10 inches deep by specifications + 2 inches for good air cushion behind.

For optimal performance there is really only one size for the box .Firstly, you get two different types of subwoofers, an open air, or closed air sub. If it is an open air sub ( hole with mesh in the center of the magnet) no ports are required, and the box should be sealed on the inside with silicone sealant. If it is a closed air sub ( no hole in the magnet) you need a 50mm port about 120mm long. If it is a 12 inch sub the box size will be 13 inches x 13 inches x 13 inches. Hope this helps

For optimal performance there is really only one size for the box .Firstly, you get two different types of subwoofers, an open air, or closed air sub. If it is an open air sub ( hole with mesh in the center of the magnet) no ports are required, and the box should be sealed on the inside with silicone sealant. If it is a closed air sub ( no hole in the magnet) you need a 50mm port about 120mm long. If it is a 12 inch speaker, the box size will be 13 inches x 13 inches x 13 inches. 15 inch, the box will be 16 x 16 x 16

I honestly would go with 2 12 inch dual 2 ohm subs and wire them one per amp. That will give you a 1 ohm load to each amp and will give the HCCA's 2500 rms per sub... It will be stupid loud... 10s hit tighter than 12's usually and 12's tighter than 15's but u will get more air movement out of a 15 than the 12's and 10s... but... 2 10's require say a 4 cubic foot box to perform well... 2 12's require a 5 cubic foot box to perform well and 2 15's require about 7 to 10 cubic foot to perform to their fullest... no matter what if you put a sub in a box that's too small it will not perform or sound like what you want it to... go 2 12's and like a 5.50 cubic foot box or a 6 cubic foot box and you will love it...

Subwoofers differ in only one way. You get an "Open Air" and a "Closed air" subwoofer, That being said, you'll have to check on your magnet which one you have to make the boxes for that sub. If it is an "Open air" Subwoofer, you should see a "wire mesh" or "grid" in the centre, at the back of the magnet. If it is a "Closed air", the magnet will be solid with no hole whatsoever.

If it is a "Open air" sub, your boxes should be sealed with silicone, and no ports are to be cut in your box.

With "Closed air" subs, you should have 2 ports below your sub and the port sizes should be around 50mm in diameter. You should start with a 100mm long piece in the one box and add 50mm increments to "tune" the port up to 250mm, depending on the frequency of bass you require.

On a 15 inch subwoofer ranging between 80Hz and 120Hz, the box size required should be around 27 liters, meaning that you will end up with a box of 16 inches high, x 16 inches wide, x 16 inches deep. Or 320mm high, x 320mm wide, x 320mm deep.
Enjoy!

Subwoofers differ in only one way. You get an "Open Air" and a "Closed air" subwoofer, That being said, you'll have to check on your magnet which one you have to make the boxes for that sub. If it is an "Open air" Subwoofer, you should see a "wire mesh" or "grid" in the centre, at the back of the magnet. If it is a "Closed air", the magnet will be solid with no hole whatsoever.

If it is a "Open air" sub, your boxes should be sealed with silicone, and no ports are to be cut in your box.

With "Closed air" subs, you should have 2 ports below your sub and the port sizes should be around 50mm in diameter. You should start with a 100mm long piece in the one box and add 50mm increments to "tune" the port up to 200mm, depending on the frequency of bass you require.

On a 12 inch subwoofer ranging between 80Hz and 120Hz, the box size required should be around 27 liters, meaning that you will end up with a box of 16 inches high, x 16 inches wide, x 16 inches deep. Or 320mm high, x 320mm wide, x 320mm deep.
Enjoy!

I would try walling it up unless you are going to buy 2 brand new subs. the problem is the older power subs had such small magnets so they needed alot less air space inside the box. Unless you can find the EXACT subs this box was made for I would recommend chopping it and doing a single sub. if you try a replacement sub go with the 12" P1 series they are a close match for the power 12's of the past.

do you want the box ported or unported (holes or no holes) if you don't got a lot of room than you dont want a ported box. keep in mind the box has to have the correct amount of cubic air space or you could seize your sub... if you're building it make sure you use OSB board (oriented strand board) or MDF board(medium density fiber) your sub needs .7cubic feet of air space in an unported box

if its the box it only needs like a 1 to 2 inch hole. i have 4 tens in my car and alls i have is a single 1 inch hole. if this isnt what your talking about try and email me back.