My current box pounds in the 30-32hz range and I love it but I also love to compete in local competitions so I need a new box for all out spl. My trucks frequency is 41hz. Can someone help me with the correct box volume and port specs for a box that will peak at 41hz for spl only? The subs are a pair of Fi Bl 18s. Thanks.

Let us know your rough dimensions you want to work with and we can come up with something for it. Its easier when we have sizing to come up with a port that makes sense dimensionally for it.

49"wide x 19"height x 36"deep are the max external dimensions I would like to use, but I can go taller if needed. My current setup has the subs and port facing the rear but everyone is telling me it'll be louder with subs up so I plan on switching to a subs up port back setup to at least try it. I'm not sure if it'll matter but the vehicle is an '06 Yukon and I'm powering the subs (dual 2ohm) by a pair of RF T10001BDs.

Hey derrick. Hope to see you at the next show- I might be hauling up 1 btl up there to see what it has in it before I rebuild.

If you're sure the truck wants 41 hz a good rule of thumb is ~ 7hz lower. I forget where you said you were tuned to, but 34-35hz would be a good starting point, but I'd really try the crx style box.

Why not make the crx box tuned the same as your current, and see how they compare? If you make it so you could interchange the ports that would save you a whole lot of time building different boxes, and you could really spend some time experimenting with the vehicle.

Its my understanding that rounding the corners (or 45s in them) will help some too. More port area will generally help too. Again, interchangable ports could allow you to experiment with the port area as well.

Hopefully someone else will have some more ideas, just thought I'd throw that out there.

Good luck.

Hey derrick. Hope to see you at the next show- I might be hauling up 1 btl up there to see what it has in it before I rebuild.

If you're sure the truck wants 41 hz a good rule of thumb is ~ 7hz lower. I forget where you said you were tuned to, but 34-35hz would be a good starting point, but I'd really try the crx style box.

Why not make the crx box tuned the same as your current, and see how they compare? If you make it so you could interchange the ports that would save you a whole lot of time building different boxes, and you could really spend some time experimenting with the vehicle.

Its my understanding that rounding the corners (or 45s in them) will help some too. More port area will generally help too. Again, interchangable ports could allow you to experiment with the port area as well.

Hopefully someone else will have some more ideas, just thought I'd throw that out there.

Good luck.

So far no matter what sub setup I've used it hits its highest scores at 40-41hz. To get the best scores I've had to tune my boxes to 32hz. I've tried tuning higher with my old and new sub setup but my scores get worse. My current box with the pair of 18s has a removable port and with anything higher than a 32hz tuning my scores drop. The sub up port back configuration will be my next test. I tried it before with my 12s and they did better with subs and ports facing the rear. Hopefully these 18s will react differently.

Lots of SUVs like subs up ports back. I have no specfic experience in a Yukon, so I cant say. Ill have to ask Shawn as I know he has done a couple installs in them. Still seems too low being tuned to 32 and peaking at 41 for a daily setup (lower pressure). But your experience far outweighs my "feeling"...lol

Id try subs up ports back, and as tejcurrent mentioned, areoports are a very easy/quick way of tweaking things to find peaks and to swap between that and a "better" daily tuning, although you seem to be tuned there already.

I have four 4" aeroports from previous installs. How many do you recommend for use with the 18s? I'm thinking of lowering box volume to 10ft.