Triticum Agricolam

An 8" port should be about 27.5" long to tune 2.0 cu ft to 45 Hz. As with all bandpass boxes I suggest making the port removable so the tuning can be adjusted after the box is playing. Bandpass boxes can be fickle things. As far as the layout goes, that's always the hardest part with these things. You may have to go with a slot port just so you can put bends in it to get the length you need.

I crunched some number is Win ISD real quick. I'd shoot for 1.2 cu feet sealed and about 2 cu ft ported size tuned to 45 Hz. 40 sq in of port area would be the minimum and 50 would be even better. This is going to make for a fairly long port though so fitting everything in the space you have available is going to be the challenge.

I completely agree with Dafaseles, you don't need that 6.5" sub. What is the dimensions of your armrest opening?

Hey man, the first thing I would do is verify your tuning frequency, its probably fine but weird things happen sometimes. The best way to do this is to get a sine wave generator app, play a sine wave tone at moderate volume and watch/feel cone movement, you are looking for the frequency where cone movement is the least, that will be the tuning frequency. Decreasing box volume generally does improve sound quality, but it usually isn't a huge change. Going from 5 cu ft down to 4.4 probably isn't going to be enough change to really make a difference. I would go down to 4 cu ft or even less. Any reduction is box volume is going to reduce output around the tuning frequency as well, but that's the price you pay.

No, that's not how it works. You will most likely be fine. The whole concept of "16 sq in per cube" is an oversimplification. There is a number of factors that go into how big your port should be for optimal performance. Things like input power, tuning frequency, etc. It actually pretty hard to have a port that's too big. At 18 in per cube I can almost guarantee it won't be too big. Too small is where most people get into trouble.

So with an aero port you would want about 70 sq in of port area minimum. The hard part is you are kinda limited to what size aero ports there are available. A 10" port will be great from a port area standpoint, but its going to have to be really long to get the tuning you want and will probably be very difficult to implement. Two 7" ports would work too, but that's a really weird size and you probably can't even get them.

Yeah, for whatever reasons, a lot of manufacturers recommend less than optimal port area for their subs. Adding more port area in your situation will certainly be beneficial though.

My suggestion would be to use more port area. Ideally I'd like to see a minimum of 75 sq in of port area based on the amount of power you are going to be running. At 52 sq in you will likely have significant port compression and port noise. Port compression can eat up half your power pretty easily, so it not something you want to have if you can avoid it.

How much power you running?

These are other parallel-tuned 6th order bandpass boxes. They have two tuning frequencies which allows you to shape the frequency response in ways you can't do with a regular ported box. That does not make them better however, just more sophisticated. If I can give you some advice, for 98% of applications a regular ported box is going to provide the best performance relative to how much space it takes up, and how difficult it is to design/construct. Bandpass boxes generally only perform better when you have a specific problem you are trying to address, and they almost always have drawbacks.

The box in the picture is symmetrical, so the left and right chambers are going to be the same volume/tuning. The center chamber would be tuned differently though. In the end its just another way to layout a parallel-tuned enclosure. Its similar to have a ported box with a port on both sides vs one port in the middle.

Nope that’s a parallel-tuned 6th order. If someone wants to go down the 6th order road those are actually the least difficult to get right.

No problem. Should be fine.

Yeah the 12-16 sq in rule is often far from ideal. It doesn't take into account input power or tuning frequency, both of which have a big impact on how much port area you need. For what you want to do, I would go no lower than 25 sq in of port area, and if you could get up to 32-34 sq in that would greatly reduce any port noise/port compression you might have. It will require a pretty long port though. Everything is a trade-off.

I can help you out with a design, you are going to need more space than just 14" H x 32" W x 20" D though. How much bigger can you go?

They have any pictures of what this looks like?

If you post your max dimensions, I can give you some recommendations and possibly a design.

This is what I would do with that amount of space. Its ~3.2 cu ft net tuned to 32 hz with just under 50 sq in of port area. If this looks good to you I'll give you a cutsheet.

Oh yeah, you can totally work within that space. Let me see if I can come up with something for you. I assume you are going to want to tune to the low 30s?

What are the dimensions you have to work with? Can't say for sure without knowing that. How much power are you going to be running?

Sure, its possible. Its going to be a fairly long port though depending on where you tune to. Layout can be tricky.

So what are you goals for this system? What kind of usable bandwidth are you looking for? Unfortunately ratios are just a really oversimplified way of designing a bandpass box. Its not that they are wrong, its just that they aren't always right. I'm glad you are looking at things in WinISD, its a powerful tool and is very useful for making comparisons between different enclosures. Just keep in mind that the frequency response you are going to get in a vehicle is going to be very different than what WinISD shows.

Good choice, I avoid MDF whenever possible, plywood is just a much more pleasant material to work with, in addition to the weight savings.

Sounds good. Loose polyfill in the sealed side is perfectly fine. Polyfill in the ported side would be very detrimental to output.

So do I understand you correctly, do you plan on adding polyfill to your ported side?