need advice for port on custom box.

[knogoodidleft 0]

Aight, Ive got 2 18" daily Fi BLs dual 1 ohm, with cooling and flatwind option. Then I got a sundown saz-3000d, iraggi alternator, and more 1/0 welding wire than you could shake a stick at.

Now I have very limited box building experince, and I know someone that knows someone, that has some experince. But I think he is limited in proper port designing, maybe.

He has a shop called 352 Kustomz, small shop, two guys, do some crazy custom stuff. Very skilled in body work.

So they start grinding away on my project, Its going to be more of a show box than a performce one. But he keeps on asking me the "port size" recommendation from Fi. I told him 5-10 cubic feet @ 30-37Hz , and I want 32Hz. He keeps on insisting that the site should give me deminsions for the port . he went to audio school. I did not say anything like, doesent the port size have to do with deminsions of box? thus different box = different port deminsions, thus no "1 port size fits all" thing.

I do not have the deminsions of the box on hand, I can call them tomorrow and get the plans. Though the plans have changed 3x, mainly for the good. Orginaly the box was going to be ~16cubes after displacement, but with a fiberglass lid, anything short of measuring foam peanuts in cubes and dumping them in until full, is going to be a guess.

was with them most of the day while they worked, should of took some more pics, and sorry for the cellphone pics, I spent money on my audio before camera .

Just did the lid today, will finish next weekend I'm off. The box is going to roll towards the front of the truck (05' silverado crewcab) pretty much going to be 1'' behind my seats all the way back with them leaned to where I drive. With the port firing right to the middle of the front of the cab, between the seats where my arm rest folds down.

coming together

as far as we got

and from this side

and from that side

friggin' sick looking

inside angle of sub <---little blurry, but you can see how it looks like from the middle going up to the sub.

Just a shell still, Going to put a ton of fiberglass on it, and a layer inside. Then gonna paint it the same color as my truck (forest green), throw a few coats of clear. And yes, When I wax my truck I'll throw a coat on my box as well. When bottom box is constructed people out side will just see the lid above the rear windows, the wood box below is going to be carpet. The faceplate/port is going to be fiberglass and colored as well.

Advice time : Should I just get dimensions and ball park cubes, then plug them into ROE or some other calculator and give him those port dimensions, or ??? I don't know.

I'm not stressing over maxing the performance out of the subs/box, I know it will have enough knock to make me smile, And look good to boot. I just don't want ports too small and have 2 18''s tuned super high, I listen to all music, mostly rock/rap then country/classic rock almost equally as much.

Thanks in advance.

Edited February 2, 2009 by knogoodidleft

[BigDaddy13440 3]

You've really gotta know the enclosure volume before figuring out the port size.

If you've got 12 cu ft gross, then you want a port with a cross-sectional area of between 144 and 192 sq in (12-16 sq in / cu ft). A single port 8" x 18" would be minimal (144 sq in), but it would only be 9" deep tuned to 34hz. That would decrease your volume by .96 cubes (if made of 3/4" mdf), dropping you to about 11 cu ft before driver displacement. I don't know the driver displacement of the 18" Fi's, but (just for instance) say they displace .25 cu ft each - now your box is 10.5 cu ft, and that same port would now be tuned to approximately 36.5hz.

Port calculator

Tune that same 12 cu ft box to 30hz, and your port would need to be 17" long. Again with the math (9.5"x19.5"x17"), you'd lose 1.82 cubes for port displacement. Add in the .5 cu ft for the two 18's, you're at about 9.7 cu ft, and the port would now be tuned to about 33.4hz.

Contact Fi, see what they recommend for a port tuning frequency for the 18's. Go from there. :bigclap: