Bandpass box for 2 SA 12s

[CleanSierra]

I've heard from a lot of reputable guys with ground pounding 4ths that ratios are not something to worry about, but it's the individual volumes for each section that you need to worry about, and that tuning doesn't play as much of a factor where as port area plays more of a factor as to how well/flat it sounds.

I hear 18-19 square inches of port per cube in the ported section is a good place to start.

I'd say 1 cube per sub after displacements for sealed, and 1.75 per sub after displacements for ported.

I'm running like 24ish per cube on mine

[ncochran]

If 2:1 is flat, would 1.5:1 be even flatter? And if so, would that totally ruin the spl? I am not trying to win any comps, but I would like to demo and move as much air as possible on the bottom end.

[Raptorman]

I gave you some advice up there ^

[CleanSierra]

The thing is, no one can tell you. It's build-specific. Your Scion has different characteristics and Resonant frequency than my Reg cab truck(and so many other vehicles too). What may work flat or peaky in mine, may have a different effect in your car. You really need to build to find out. I'd start at 2:1, and then make adjustments on ratio after you've tested awhile.

[ncochran]

Right on, thanks! Will see what I can come up with hehe. Am waiting to find out if I need surgery on my spine/shoulder then am gonna start build. Should be about 2 weeks. Just trying to compile as much info as possible before I start.

[Bradprobert]

I have 2 sa8v2s in a 4th order and here are my mistakes that may answer some of your questions.

1. not enough port area. i had 50 sq in which was half my cone area. it would be best to mulitply that by your xmax to get a better estimate of what your port area should be.

2. ratio was slightly too big. it was about a 3:1 ratio. if i could do it again i would do a 2:1.

any questions let me know i smashed my finger at a party so its kinda hard to type lol

[ncochran]

I can squeeze about 6.3 cubes out of that cargo space and still keep it level with the back seat. If I have to go taller it will suck but I might have to lol.

Bradprobert, thanks man! Good stuff.

Edited June 2, 2013 by ncochran

[ncochran]

Just to share some info. Jacob from Sundown recommended .75 sealed and 1.5 ported per sub, tuned to between 40 and 45. The only thing he didn't mention was port area. I will have to figure that one out on my own, but there is definitely some good info here I think. I think I can fit that box in my space. Figuring 1.5 sealed, 3 ported + port/sub/bracing, I think I can get that somewhere in the ballpark of my available space.

Edited June 3, 2013 by ncochran

[RobertR]

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

Good read for 4th order boxes ^^here^^

[ncochran]

Thanks! I have read that one a couple of times already but I appreciate the post anyway (I just read the whole thing again lol)

There is one final detail that is fking me up right now. And that is port area. I imagine the answer is going to be for me to experiment lol. But...

If Jacob recommends .75 sealed and 1.5 ported that leaves me with 3 cubes ported for the 2 subs. Most recommendations are for massive port area (1/2 sd of subs or around 100 inches of port area in this case). Most recommendations are also to keep port ratio at around 15 inches per cube. The tuning I can handle, gonna tune it around 40 to start, and chop my way down as far as needed (probably settling closer to 50 if I had to guess). But I can't follow both recommendations on port area at the same time lol.

I wish I had a termlab lol.. I am the type of guy that would spend every waking hour tweaking and testing, but I just can't swing a meter right now hehe.

I think I will build 3 seperate load walls and ports, and go with those barbed insert nuts (or whatever they are called) for the load walls. One will be 15" per cube (so 45" total), One will be about 22 per cube (66" total) and the other will be a massive 33 per cube (almost 1/2 sd of subs).

Also is there a difference between port requirements for 4th order walls and 4th order ~normal~ enclosures? Maybe that would account for the differences in port suggestions?

I really apreciate everyon'es input here. Hopefully this thread will help someone else. As I start the build I will update both my build log and this thread with results. And if anyone in the Hampton Roads area or in Northern NC could lend me some time on their Termlab (or any other meter for that matter), I am guessing I could share much more meaningful results. If so, hit me up! Also, please continue the discussion, I haven't started building yet hehe.

Edited June 4, 2013 by ncochran