Bandpass Box...

[jimbo_limited]

I have a Bandpass box for my three twelves and each sub has its own chamber. My problem is that the woofers dont sound as "boomy" as it should with the bandpass encloser. My friends dual twelves hit harder than my three twelves and has they the same type of sub box but his twelves share chambers.

My specs for the box is

1.1 Cu Ft per port chamber

About .46 Cu Ft per sealed chamber... 1.4 Cu Ft total

The port size are 2 5x5 inch for side subs and 2 4x5 inch for center sub.


Here is a picture of my box

http://i17.ebayimg.com/06/i/000/81/66/c5c5_1.JPG

[D.Kreft]

On Feb 4, 5:59 pm, jimbo_limited <jimbo_limited.
> wrote:

> I have a Bandpass box for my three twelves and each sub has its own
> chamber. My problem is that the woofers dont sound as "boomy" as it
> should with the bandpass encloser. My friends dual twelves hit harder
> than my three twelves and has they the same type of sub box but his
> twelves share chambers.

Well, I'm not sure what you mean by "hit harder"--that's a pretty
loaded term. Ask ten people what "hits hard" means and you're likely
to get about eleven different answers.

There could be several things going on here...

1. You may have a bad bandpass alignment.

Bandpass ensloures are remarkably picky beasts--screw up just a little
bit and you'll wind up with an enclosure with a gross frequency
response curve, horrible group delay, or both. It's absolutely
critical that such an enclosure be designed *specifically* for your
drivers and to fit your system as best as possible.

It's a big red flag to me that you've got three drivers in this
cabinet and you have two of the drivers tuned to the same frequency,
but one driver tuned to something completely different. Whoever built
this thing is demonstrating that he doesn't have a really good grasp
of how this stuff is all supposed to work together...your two outer
chambers are tuned to a wildly different frequency than is the middle
chamber. I would not be surprised if the one sub is effectively
cancelling-out part of the work being done by the other two subs. Have
you tried disconnecting the middle driver and seeing what the system
sounds like with just the two like-tuned subs going? I would almost
bet you'd get an improvement in sound, providing that the alignment in
those two outer chambers isn't complete FUBAR.

2. You may have really weak midbass drivers or have midbass drivers
that are not in phase with the subwoofer at adjacent frequencies.

Bandpass enclosures have not only a high-pass that cuts off the very
low frequencies, but it also has a low-pass that cuts off the highs--
this is why it's called a "bandpass"--only a relatively narrow band of
frequencies will be produced by the subwoofer system. Because of this,
you have to have *really* good midbass drivers to make up for what the
subwoofer enclosure naturally filters-out. A more conventional system
(sealed or ported) does not inhibit the natural harmonics that would
otherwise reinforce midbass performance, which could be what you're
expriencing in comparing your system to your buddy's system.

Also, by "in phase" I'm not talking about the polarity (+ and -) on
your speakers. Phase isn't just as simple as making sure that all your
"+" and "-" terminals are hooked-up properly. Thanks to the magic of
filtering, you can have a situation where your subs and midbass
drivers are, say, 100 degrees out of phase with one another at a
particular frequency. It's pretty complicated stuff, and adding a high-
ordered cabinet like a single-reflex bandpass doesn't help (dual-
reflex and series-tuned dual-reflex boxes are even worse).

3. Your ports may be effectively choking your drivers.

Think about it...a 12" sub has approximately 113 square inches of
surface area with which to compress and rareify the air in your car. A
pair of 4" ports gives you approximately 25 square inches...which
might be enough to prevent port whistling, but you're not going to be
able to reproduce the same viceral sensation on transients (i.e.
kickdrums) when you drastically cut the effective piston area by
roughly 75%.

> My specs for the box is
> 1.1 Cu Ft per port chamber
> About .46 Cu Ft per sealed chamber... 1.4 Cu Ft total
> The port size are 2 5x5 inch for side subs and 2 4x5 inch for center sub.

Unfortunately, without the Thiele-Small specs for your subwoofers,
your box volumes and port specs are absolutely meaningless.

It sounds to me like you need to consult with a professional
installer, preferably with one who has experience with your particular
subwoofers, who can help you find the optimal subwoofer enclosure to
suit your car and your tastes.

-dan

[Matt Ion]

D.Kreft wrote:

> Unfortunately, without the Thiele-Small specs for your subwoofers,
> your box volumes and port specs are absolutely meaningless.

Assuming the subs themselves are cheap garbage to begin with! Somehow, it
wouldn't surprise me if they're some kind of $29.95 specials.