Rate my 4th order design please.

[Triticum Agricolam]

My understanding of a 4th order is that tuning frequency is where youll see drop off in output. So this box would be loud from whatever lows the sealed will allow up to 46 hz. Not the case?

Yeah you pretty much have it right. The problem is with a front chamber of that size you are getting so much boost in output from the front chamber the output from the rear chamber below tuning kind of becomes irrelevant. So you have a big peak in output right at your tuning frequency and then things drop off quickly both above and below that. Its a one-note-wonder.

[CleanSierra]

Build it and see how it goes. That port area seems a bit low to me. I like LOTS of port area in a 4th order BP though. My blowthrough box has 264" for 4 12s tuned around 48. The truck peaks at 44(resonant frequency of a regular cab GM).

My box smashes from 32-55 pretty well and does a 150 from 35-47ish(solid 10+ Hz bandwidth over a 150) on 4K.

[germanyt]

Cant afford to build it and see how it goes. Someone is buying the wood and im building the box. There cant be any re-dos. I don't need a fart box. Just something that'll play music and be loud.

[CleanSierra]

All the modeling and guessing in the world won't guarantee success on the first shot. Bandpass boxes aren't typically "nailed" on a drawing board or on the first attempt. A box IS built and tweaks are made once you know how it performs.

So it's cute that you want it perfect on the first run but good luck on that.

No one here can guarantee you that you'll be musical or loud. All we can do is guess, just like you.

[afrakes]

Then maybe it would be beneficial to propose some ideas on a box that can easily be "tweeked". Things as simple as using aero ports so you can find the tuning that sounds the best. I know u really can't tweek chamber sizes once they are glued into place, but some adjustment on one box is better than a set in stone final product hoping it sounds good.

[Triticum Agricolam]

+1 to what CleanSierra said.

The only way you are going to know for sure what the box will sound like is to build it. I can show you what the raw output should be using software, which can be useful for comparing design changes, but that's assuming the T/S parameters are accurate and it doesn't factor in any cabin gain, which will change the sound significantly.

My suggestion would be to make the port removeable or otherwise adjustable. It's a lot less work to build a new port vs building a new box. If the front chamber ends up being too big you can always use filler blocks to take up space. There are things you can do to tweak the design after its built but it's a lot easier to do if you plan ahead.

[germanyt]

Thats a good idea. I had been thinking about a removable port luke Meade's. I just don't know whats the best method of installing it. Double up the loading wall with a cutput and recess large enough for port to bolt in place?

[Triticum Agricolam]

Thats a good idea. I had been thinking about a removable port luke Meade's. I just don't know whats the best method of installing it. Double up the loading wall with a cutput and recess large enough for port to bolt in place?

Yeah, that's pretty much how I do it. Your port should just have a big flat flange on the end that you can bolt/screw to the face of the box.

[afrakes]

How do you keep that area from leaking air though? My first thought is weatherstripping but unsure how that would hold up?

[germanyt]

How do you keep that area from leaking air though? My first thought is weatherstripping but unsure how that would hold up?

I'd think a fat bead of silicone would do the trick and be easy to remove if need be.

I've been doing some reading on the caraudioclassifieds 4th order thread. 1000+ posts actually. Thinking of going with a new ratio. 3:1 with 1 cube sealed per sub. So 4 cubes sealed and 12 ported. I ran across a formula for determining sealed resonance in that thread and am using it but coming up with silly numbers. The square root of Vas/Vb+1? Not sure I'm doing it right. My impression is that the answer to this formula will give me my best ported tuning frequency. Also, is it okay that I fire the subs at each other in the box? Soundqubed assures me that it won't cause any cancellation but I've heard one person say it's a general 'no-no'. Build begins this weekend BTW.