I need some help in designing a Band Pass ported box to take 2 Kenwood 12" 250wrms single voice coil sub on the boot (where else) of a TR magna. I've got a custom sealed box now, but ive heard good things about a well designed bandpass box. any help or links will be good.

Ive included pics of the amp and subs if these help, as i can remember modle names

Bandpass boxes are very ticky things to make. you actually need to get TWO box dimensions near-perfect for them to sound good. If they are out by even a tiny bit, all that gain that you can get out of them is lost, and it just sounds crap.

For the unititiated, Bandpass boxes is just both a sealed and a ported box which have the EXACT same tuning frequency stuck together. The sub(s) sit inside the box on the divinging wall between the boxes. The subs usually fire INTO the ported side.

Large amounts of gain and stratospheric SPL figures can be extracted from bandpass boxes. Those '150dB Plus from one 15" sub' type cars are using bandpass boxes most of the time, which are also tuned to the vehicle's resonant frequency also.

The problem with bandpass boxes is that they sound very one-dimensional, having a big spike in gain around the tuned frequency at the expense of frequency response across the whole sub-bass range. A bandpass box will generate 7-8db gain at the tuned frequency, a recommended ported box about 3dB, however it is a much flatter frequency response curve.

That said, most of the commercial 2x12" subs in a bandpass box you can buy at JB's, Autobarn, etc etc are mostly pretty good as the manufacturers have spend alot of R&D money getting the design right for best performance. They also sacrifice some gain for better frequency response - say maybe 4-6dB gain.

The biggest thing is getting BOTH chambers of the box tuned to the SAME frequency in order to get the gain. 1mm out on any of the measurements is enough to make it sound horrible. I have heard a couple of home-built bandpass boxes, and they got owned by my twin JBL GT4-12's for SQ! Mine was much louder too.....

If you really want a bandpass box, go to a JB's or Autobarn and get them to throw a demo box into your car, and wire it up to your amp. Have a listen, see if you like it.

EDIT: I won't mention anything about the Kenwood sub, except that I would not be sealing them inside a box as I think it would need replacing fairly quickly once you start feeding them the power that a bandpass needs to get going. There are better, cheaper subs on the market that are much more suited to bandpass duties, mainly the "american brands". When I think bandpass, I think of Audiobahn first - they have some very nice factory bandpass boxes with 2x12's for about $600. JL, JBL, Cadence, fusion, they are all up there too. The bigger and beefier the subs are, the better. Massive magnet structures and huge rolled surrounds for big excursion is what you are looking for.

Dude the time and money involved with doing the whole bandbass thing isn't worth it for everyday driving. Putting those subs in a ported box to suit is a much easier way to get those few db. Plus it will sound much much better.

If you had to go bandbass then look around into 4th order for those subs, use a common sealed chamber that they both fire into and have separate ported chambers tuned to the same Hz.

Really if you want to get a whole lot louder, you may want to look into sub(s) that are designed to do so with power to match :D

wood is cheaper than subs and amps

The cost to get a bandbass box made by someone is between $300 and $600 or more if you want perpex, turbo ports, vinal, carpet etc etc.

Find the model number, it will be KFC- blah blah and if you have the book get the T/S which has the Vas, Qtc, Qes etc on there so we can work it out. If not search the web to find the specs and then post them up.

i dont want someone else to build it, i want to build it, im at home with a broken wrist, so ive got a lot of time on my hands

Yes but what I am saying is that it is very hard to do and will cost lots of money to get it done properly. Sure you can build it yourself but you will probably be dissappointed at the result. Can you find the T/S?

You want Good Results with not alot of money???

Megavox had Two 12 inch Bandpass Enslosures loaded with some generic subs.. Went Hard for $250..

RT Design or Vibe make the Best Bandpass enclosures ever..
but they cost more then the Average Widescreen TV

This is Similiar to the Megavox one I have seen before

http://207.142.131.37/fullsize/BPASS12X.jpg


A Kenwood Twister wont last Very long in a Bandpass enviroment...
they are just not built to take the punishment a Bandpass will require from it..




Bandpass are my favourite Sort of Enclosure...
I had Two 10 inch Pioneer Diamond Plate subs in Seperate Bandpass enclosures and it Was Bass Heaven... a Bandpass enclosure when Tuned correctly can make a 12 inch Sound like a 15 With the Rumble and a 10 inch with the Punch..