Need Help Designing a 4th order blowthrough

[Bubohms]

Looks like a parallel-tuned 6th order would work pretty well. They aren't without their drawbacks though.

Compared to a 4th order bandpass box a parallel-tuned 6th order will get you wider bandwidth, more low frequency output, and smoother frequency response. All good things. The disadvantages though are its significantly more complex to design/build, will require a much bigger opening between your bed and your cabin, and will probably be an overall larger box.

Anyway, if it's something you are interested in I can post frequency response graphs showing the differences in output, cone excursion, etc.

Yeah that sounds good

[qu1cks1lver56]

Tuned in because I know nothing about 6th orders except I've heard some great sounding, loud ass 6th orders and want to learn and build some.

[Triticum Agricolam]

OK, here are some graphs comparing a 4th order bandpass vs a parallel tuned 6th order bandpass.

Frequency response:

The red line is the 4th order box (4 cf sealed, 7 cf ported @ 45 Hz), the blue line is the 6th order design (10 cf @ 30 Hz, 4 cf @ 55 Hz).

From a frequency response perspective, the 6th order box gives you pretty much the same peak output, but has a MUCH wider frequency range and will provide significantly more output in the 25-35 hz range. It will also play well up 65 hz or higher.

Please note this graph does NOT include any cabin gain. With your vehicle cabin gain should boost low end output significantly. Just how much is impossible to tell.

Cone excursion:

Again, red line is the 4th order box, blue line is the 6th order. The red horizontal line is the Xmax of the HDS212 subs.

The 6th order has lower cone excursion over about half of the usable frequency range. Of particular interest is below 35 hz, where the 4th order is pretty much maxed out, the 6th order box still has room to spare. You could probably get away with putting more power to the 6th order box, at least from a cone excursion perspective. With the 6th order design a properly set subsonic filter is required, just like with a regular ported box.

Based on the graphs, the 6th order design is better is pretty much every single way, but graphs aren't everything. The 6th order design is a larger box, it's a good bit more complex, and these designs can be rather difficult to lay out. It's basically two ported boxes attached face-to-face with the sub sitting between them, routing the ports so that they exit where you want and you get the proper port lengths is usually the difficult part. Sometimes you just can't make it work out. You are going to want at least 120 sq in of port area for the rear (30 hz) chamber and at least 100 sq in for the front (55 Hz) chamber. Like with any other bandpass design, I strongly suggest you make the ports adjustable so you can tweak the tuning if needed.

I'm not trying to push you towards one design or the other, they both have their advantages and disadvantages.

[Joe X]

And here is the same as above with average cabin gain factored in (orange 6th BP, red 4th BP):

Here is the same but added a ported enclosure (yellow plot) 10 cubic feet net @34Hz:

A ported box placed instead of the rear seats would be by far the easiest and cheapest to build and it seems it would have pretty much comparable performance to the bandpass boxes presented. Is hard to justify the challenge and cost of building a blowthrough to install entry level stuff.

[Bubohms]

I was going to do the ported box but then I wanted to keep my back seats so that's when I decided to do the blow through but now i don't really know what to do haha.

[MrSkippyJ]

The blow through can be ported, right?

[CleanSierra]

The blow through can be ported, right?

Only way would be more of a clamshell type of design with the subs on a V and port in the middle. I would suspect quite a bit of metal would need to be cut as well to accommodate that design.

[MrSkippyJ]

Ahh that makes sense. I'm a noob when it comes to blow throughs

[Bubohms]

I've decided to do a sealed box in place of my back seats so if anyone could help me with a design on that that'd be cool

[Joe X]

Not sure if you mean you want to seat people over the box but sealed would be very inefficient.