custom made2x12" bandpass box with port firing from ski

[Guest]

ive got 2x12" infiniti kapa series 300rms 1200watts each in a free air exogon shap box it is loud!! with infinti conponent speakers in the front and 6x9s in the rear shelf but the boot rattles like hell i dont think any soundproffing will stop it so i was thinking of geting my mate to build me a bandpass box for my 2x12" with the port firing through the ski hole that way the sound is pushed through to the cabin and not rattling the boot,the free air boxes use the boot as a cavity so it acts as somewhat a bandpass would any one be able to tell me if it would sound better or LOUDER with a bandpass or a free air box in a 1991 on H plat 325i sport any feedback would be great as i dont like the weight of the boxes as its 65 pounds 2gether with the subs and does slow me down when im driving sideways the car

[amit325i]

the rule is this- ported boxes marginally not louder than sealed, free air subs work well on a specified volume (too tricky to get right)

Ported goes much lower than sealed, which is what i prefer and it goes loud enough that my ears hurt with the bass pressure!

2 12's to get the best out of them will require a large box, = heavy, better for you as a compromise is to build a custom ported box for your 1 12' and tweek the sound from your amp, I would recommend your amp has a variable cross over, as my amp is variable from 30hz to 150hz.

Get the spec from the manufacturer regarding box dimensions, this would be in cubic feet, i have a 2 cubic foot box with a 4 inch diameter/ 10.9 inch length port for a rockford HE 12 sub.

the main rattles in the e30 is the number plate surround and number plate, i removed and fitted some foam adhesive strips and the rattles are gone, i have not done any other sound proofing yet, don't need to, there is a slight rattle from the boot lid at high volumes but you can't notice it unless your in a quiet place.

[mrLEE30]

I have a 3cuft box with a 12in JBL with a 4inch port and 13inch length firing sideways to the left as you see the picture. Boot was not soundporoofed but as amit says the number plate boot and the air flaps behind the bumpers rattle. if you have a ski flap then you shouldnt' have this problem as enough air can move into the cabin,mine is a cab so to get around this i ran lenghts of pipe from the boot into the cabin under ther back seat foam to allow air movement as the cab boot is well sealed. take a look, i reckon it sounds well good, nice and low, plenty of resonance. but dont forget if you are designing a box to remember that you need to get it out on a sh$tty dark night when you have a flat tyre. Oh yeah if its weight you are worried about then junk the spare, buy a tube of fix-a-flat and use the spare wheel well space as extra volume when you design your box.

mr lee

[Markymarc]

bandpass boxes deffinatly work in a e30, i got 2x10" diamond audio subs in a custom bandpass box with 2 4" ports by 13cm long which come through the rear shelf. you can have it turn right up and not a rattle from the boot or no plate to be herd, and it is loud,got it tested and was rather impressed with the 132db it produced
when i brought the subs i was gonna get 2 12"s, can't help but wonder what that would have produced