Need advice on building a 4th order bandpass

[cashmonkey38]

Hey guys, new to this forum but have looked through some old posts and saw a lot of helpful info given by members so I thought I'd try this place out, not having a lot of luck elsewhere. Here's my situation - have two 12's that I know from experience have the potential to be very loud, but the box I have them in now (I'm pretty sure) is too small with too small of a port (I built it off specs someone gave me for free, without really checking anything) and I want to build a new box. Also the box I have now is fairly loud, but with the back seats in my car a lot of bass is lost - have confirmed others have had this issue with my type of car. So looking around a little it seems like the best option would be to build a bandpass box that is ported up through the rear deck of the car, have read that a ported box will not have the same effect that a bandpass would have when used in this manner, no idea if this is actually the case or why

So - I don't know a lot about designing bandpass boxes, or really about designing boxes in general. I wouldn't have too much trouble fabricating the box, it's more of designing one based on what would be best for the subs I have and so forth. Basically I need help figuring out how much ported box and how much sealed box I need for my subs, and the ratio of the two, and since this box will be ported through the deck I need to know if this will affect the box beyond port displacement, seems like bandpass boxes have a lot more factors than ported. That being said I have to build the box to go over this shelf in my trunk that the gas tank is under, so also wondering if that's going to affect the bandpass or if I can just build it any way so long as ported and sealed volumes equal a certain number, I can post pics if needed.

Any help would be appreciated, and I would be willing to pay for a decent design I just don't really know what to do on it. I'll paste the info for the low end of my system below. Thanks guys!

Subs: Two 12" Rockford Fosgate T2D212's 1200w RMS each

Amp: Kicker ZX2500.1 2500w RMS at 2ohms

Current box is 2 cubes net internal, so yes 1 cube per sub, slot port is 12" x 3" and tuned to 30 or 32hz

Full specs for subs:

Power Handling (Watts RMS): 1200 Watts RMS
2400 Watts Max
Voice Coil Diameter: 4.0" (101 mm)
Magnet Weight (oz): 292 oz. (8.28 kg.)
Speaker Connector: Compression Terminal
Fs (Hz): 38.7
Re (Ohms): 3.4
Le (mH): 1.64
Qms: 5.15
Qes: 0.54
Qts: 0.49
Vas (Liters): 13.6
Sd (cm2): 430
SPL (dB @ 1w/1m): 83.5
Xmax (mm): 22.32
Woofer Displacement (in): 0.151 cu.ft. (4.28 Liters)

[cashmonkey38]

Ah also my car is a Mercury Marauder, very similar to a grand marquis

[Meka]

http://www.stevemeadedesigns.com/board/topic/126478-basics-of-a-4th-order-bandpass-enclosure/

[cashmonkey38]

Thanks for the info. So does the shape of the box not matter at all so longer as the ratio and internal volumes are correct? And should I just use the manufacturers recommended for the sealed side? Also why does he say to tune around 45hz, is there a particular reason not to tune down around 32hz? I've found that's what I like for ported

[BEEMDUB]

Thanks for the info. So does the shape of the box not matter at all so longer as the ratio and internal volumes are correct? And should I just use the manufacturers recommended for the sealed side? Also why does he say to tune around 45hz, is there a particular reason not to tune down around 32hz? I've found that's what I like for ported

what shape are you wanting to make the box? and yes use the recommended for the sealed side, it should be a 2:1 ration between the sealed and ported side... and tuning is not the same as a ported as it is for a 4th...45hz for a 4th order is the equivalent of low 30s in a ported so I would tune it to that if I was you

[Eroc3k]

hmm interesting

[cashmonkey38]

Thanks for the info. So does the shape of the box not matter at all so longer as the ratio and internal volumes are correct? And should I just use the manufacturers recommended for the sealed side? Also why does he say to tune around 45hz, is there a particular reason not to tune down around 32hz? I've found that's what I like for ported

what shape are you wanting to make the box? and yes use the recommended for the sealed side, it should be a 2:1 ration between the sealed and ported side... and tuning is not the same as a ported as it is for a 4th...45hz for a 4th order is the equivalent of low 30s in a ported so I would tune it to that if I was you

Noted, yeah I'm just trying to make it whatever shape will fit, most likely just a large rectangular box, but again I need to port through the rear dash so the port will be coming out of the box and extending to the deck. Question about that - what's a good way to calculate what the port dimensions should be? Looked at minimum area on one calculator and it said 80in but when I checked the 'band pass' box it shot up to 250?? Is it different for bandpass?

[cashmonkey38]

So should I just calculate the tuning for the ported section as if it was a regular ported box?

[CleanSierra]

My advice is to go with someone like Ram Designs or a professional box designer so that its a design that will work. He will charge you for a design but he will give you a picture and a cut sheet so you can just make your cuts and assemble the box. If this is your first bandpass, I'd highly suggest having someone like Ram Designs or Bass Heads Ent. design you up a box. BHE is kind of backed up right now but you can email them nonetheless. I don't think Ryan at Ram Designs is backed up currently but I'm not sure.

You want to calculate the tuning to be higher than a normal bass reflex box. Typically, tuning on a bandpass 4th are in the mid to high 40s and even into the low 50s. Your low end response comes from the sealed chamber and your high end roll off comes from the ported chamber in a bandpas environment. I'd suggest looking into Aero ports since you're wanting to kind of port through the deck. id sound deaden like crazy on that shelf to avoid rattles as well.

Port area suggestions will vary if you search around the forum and you'll find much debate. if you had a 2:1 ratio and had 1 cubic for per sub sealed(2 cubes total) you'd get 4 cubes ported. If you wanted to tune at say... 48Hz, I'd do two 6" aero ports. After port displacement is where you want your 4 cubic feet net(and subs depending on if you wanted them in the ported or sealed chamber). 2 ports that are 6" diameter and for 4 cubic feet would need to be JUST a little over 12" long. That should be enough port to avoid any kind of noise and perform well.

[CleanSierra]

If you want more specifics, PM me or message here