i asked a friend of mine who is very knowledgable with car audio (but puts a lot of stock in modeling programs, which i dont) to help me with the port designs on my box. i was shooting for a 4 ft^3 @30 hz box, when i asked him about it, this is the reply i got. he recommends 33hz, but i was shooting for 30 because i want this to hit LOW.

To be honest with you, I think 4 cubes for those 2 subs is too big. The Qts on these subs is so low, that they really want a smaller box. I found that 1.5 cubes (each) tuned to 33hz gives a nice flat response. With the 1.5 cubes per sub (3 cubes total), you'd need 2 4" ports at 17.4" long each, or 3 3" ports at 15" long each.

If you jump up to 2 cubes per sub (4 total) tuned to 30hz, the response thins out between 40 and 70hz, which I feel will hurt your overall bass response. But... at that size, your ports would be 15.5" long for the pair of 4" ports, and 13.37" long for the 3 3" ports.

i was thinking 2 ft^3 was perfect for a ported rl-p 12. should i go ahead and do the 4 ft box or take his advice and do only 3? for the ports im using 2 4 inch aeroports. are the lengths he gave me about right? anyone else have any thoughts on this? if i have to, i can build it another inch and gain about another cubic foot, so i can go up to 5 if i have to.

also, its goin in a firebird trans am, so the design is quite unorthodox. here is a picture of my current sealed box. im basically going to build the same thing, just with a rectangular section extending about 1 and a half feet up to the backs of the back seats.

Edited March 13, 200619 yr by Slumpin

Here are your numbers:

4 ft^3 two 4" ports at 15" = 28 hz.

3 ft^3 two 4" ports at 15" = 33 hz.

4 ft^3 two 4" ports at 17" = 27 hz.

3 ft^3 two 4" ports at 17" = 31 hz.

go with at least two 4" ports, not three 3" ports. Thoes woofers move a lot of air and if you under port them you will have major chuffing. I would even suggest two 4.5" or 5" ports

4 ft^3 two 4.5" ports at 15" = 32 hz.

3 ft^3 two 4.5" ports at 15" = 37 hz.

4 ft^3 two 4.5" ports at 17" = 30 hz.

3 ft^3 two 4.5" ports at 17" = 35 hz.

where would i find 4.5 inch ports? this is what i was looking at, didnt see any 4.5 inchers there.

http://www.partsexpress.com/pe/showdetl.cf...tnumber=268-352

When in doubt, you can always run to your local hardware store and rig up some PVC pipe in all sorts of lengths and sizes. Of course, they won't have that nifty built-in flare, but you could rig that up too if you're so inclined! I'd personally run with 2 cu ft per RL-p12, tuned to 28 Hz (at least 20 square inches of port area per driver would be ideal, since as I'm gathering, your woofers and port will be firing into the cabin of your ride, and you definitely wouldn't want to have port noise in there).

yeah the subs are going to be just like they are with this box, with the ports firing straight towards the front of the car. i think i could also fit them in between the woofers, firing straight up, might that sound better, being at the very rear of the car?

Edited March 14, 200619 yr by Slumpin

ok well i got the 4 inch aeroports, and finalized the design for the box. i had to make it bigger than i thought in the front to accomadate the ports, and angle the woofers towards the back to fit under the hatch towards the rear. however i ended up with a lot more space than i thought, it looks like i have 5.06 cubic feet before the ports and woofers. if i remember correctly the rl-p 12's displace .18 each, so that leaves me with 4.7 before the ports.

when i subtract the ports volume from the box, i subtract in entire volume of the inside of the aeroport right?

when i first did it it was way too big, so i took away the very bottom section, the real skinny piece at the bottom. if i wanted to, i could build this back in and have enough room for 2 ported 15's (rl-p's of course)

i have the 2 4 inch precision ports from parts express. i believe they're 18 inches long before being cut. would that be enough port for a pair of 15's, or wouuld i need a third?

> when i subtract the ports volume from the box,

> i subtract in entire volume of the inside of the aeroport right?

Net internal volume, is the effective useable airspace by the subwoofer, not including the displacement of the driver itself, any bracing, the walls of the enclosure, including the entire port. Entire port meaning, the volume inside the port, as well as the volume of the material that makes up the port.. since obviously that material wouldn't be "useable airspace".

> i have the 2 4 inch precision ports

Two 4" round ports come in at about 25 square inches of cross-sectional area. Definitely not enough for two 15's, as you're ideally aiming for 35 square inches per RL-p15! With the flared precision ports, you can go a little lower, but I wouldn't go as low as 25 square inches even on a single RL-p15.

Them b