Need help on designing a good sub box or wall

[BAMABOY691]

I need help on designing a good box to handle the lows. I really dont want a wall but if I have to I will but I got three 18s re sx and need a good design the box im using for now two on top and one in front inverted its 38x24x24 the max space I want to use is 38"wide 28"long and 36"high only because I still want my back seat

[Stephen Raab]

So you are going to need more space for those subs..... you need about 5.5 ft3 per sub at a minimum..... so 16.5 total. Your dimensions give you about 12.6 ft3.

[BAMABOY691]

I know that much, I was asking for a different design some sort of 4th order or so. I have ideas Im going to post pictures of them and my box now .......really just want a couple of opinion for real....

[CleanSierra]

A 4th order bandpass takes up much more space than a regular bass reflex box(also a 4th order). So if you barely have room for two in a regular vented cabinet, you definitely won't have room for two in a bandpass 4th order.

That IS, unless you want to do a 4th order isobaric bandpass(those subs likely won't be good for that kind of loading).

Here is an isobaric 4th order bandpass I built for a local guy:

That would be about your only option if you want bandpass and both subs. If you want to run all three in a vented enclosure, you don't have space.

I didn't run your dimensions, I'm trusting the other guy's math from earlier in this thread.

[BAMABOY691]

But I thought thats what a 4th order box is for to maximize the small space........Well heres a picture of my current box and a UGLY sketch of the design im shooting for: [{IMG}[{IMG}[{IMG}[{IMG}

[CleanSierra]

A 4th order bandpass does not utilize space unless it's an isobaric loaded bandpass. A typical 4th order bandpass has the sealed and ported dimensions for the sub or subs in question. Because of this, the box is larger than that of a sealed box, and larger than that of a bass reflex(also known as a 4th order, just not bandpass), which is a regular vented cabinet.

Your design has a problem with it. You have that one sub firing directly into the port. You could have problems with that sub unloading and it will certainly "act" different than the other two. You could also experience cancellation in that design with the opposing two subs dieting at each other.

[CleanSierra]

I just ran the math on the dimensions you want to run. You have 13.7 cubes available. What kind of volume on the sealed and ported side are you wanting to use for this bandpass design?

If running, 3.5 cubes per sub sealed and keeping it at 3.5 ported, that's 21 cubes needed before any displacements are considered. The subs displace some of the volume as well as the port. Not to mention, that's only accounting for 3/4" of material on all sides. It's likely have some doubled up walls on that box or some good, GOOD bracing.

[Joe X]

But I thought thats what a 4th order box is for to maximize the small space........Well heres a picture of my current box and a UGLY sketch of the design im shooting for:

[{IMG}

Please man read something before grabbing a pen:

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

[john253a]

That just looks like a sealed box with the subs inverted

Idd just build your wall

38x28x36

Through in 6x 6" psp aero ports 17" long

Idd do 2 subs on bottom facing fwd

1 centred on top and 3 ports either side at top

[john253a]

38x28x36 in 0.75 is 19.3 gross

After bracing and double baffle front it's 18.5gross

So it doable with aero ports only just