6th order bandpass design advice.

[carlife]

Hello all.

Wanted to ask for some advice. I have been building and working on cars for the past 15 years, but have never done a bandpass box. I have been following Doug Bernards build and want to build something exactly like that.

Can someone tell me how I can determine what kind of box size for the front chamber and for the rear chamber? I know a lot has to do with the TS parameters of the woofer, but I am pretty open on which woofer to get as well. I have always used JL but open to Rockford, CT sound, sundown or whatever you can advise best for a bandpass box.

I am looking to do a single 10 or 12 as I am limited in space.

Here are my questions:

Can you tell me how I can determine the ratio or sizing for the woofer of choice when building the box?

I already know length x width x height

Also can you tell me how I can determine the port length for both chambers?

Whatever else you can give me would be great information and appreciated as well.

Thanks.

[Triticum Agricolam]

Doug built a parallel-tuned 6th order, which is definitely the easier of the two to get right (the other being a series-tuned 6th order). Parallel-tuned boxes are larger though.

WinISD can model that style of box and that (or other simulation software) is probably going to give you the best chance of success right off the batt. As far as subs go, any sub that works well in a ported box should work decently in a parallel-tuned 6th order BP. Since the chambers are separate, tuning them is exactly like tuning a regular port box (unlike series-tuned BP6 boxes). There are no standard "ratios" you just have to size the chambers independently.

[carlife]

Thanks for the reply Triticum. Forgive the ignorance, but maybe you can help the light bulb click in my head. Say for instance a JL audio's website says a 12w7ae wants 1.75 cu feet to be tuned at 36.7HZ with whatever slot port size it is specifying. Do I split the 1.75 cu feet in half? One for the front chamber and one for the rear? I believe the port sizing will determine the tuning frequency. How do I determine the length of the port? I have winisd but am new to it.

[Triticum Agricolam]

So to understand how parallel-tuned 6th order bandpass boxes (BP6 for short) work, you first have to understand what a regular ported box does. As you make a ported box larger you get more output, but only around the tuning frequency. If you make a ported box too big you get peaky, one-note-wonder bass, along with other problems. With a BP6 you get two chambers that can be tuned differently. The lower tuned chamber (also called the rear chamber) handles the low frequency output. Then the higher tuned chamber (front chamber) handles the higher output. By changing the size and tunings of these chambers you can get more output out of a sub without getting the peaky bass you get from a large ported box. You also have a LOT of control over the frequency response of the sub. These benefits come at the cost of a larger box and increase complexity.

Here is an example:

The green line is a 12w7 in 1.75 cu ft tuned to 36 Hz. The blue line is a BP6 with a 3 cu ft rear chamber tuned to 28 Hz and a 1.25 cu ft front chamber tuned to 55 Hz.

The BP6 has more output through most of its usable bandwidth, it really kills the ported box below 40 Hz. It also has fairly flat frequency response. Its over twice as big though, so that's the price you pay.

When it comes to determining port sizing you calculate tuning like a regular ported box. You can use WinISD for this or an online calculator. As with any bandpass box, I recommend you plan ahead and make your ports removable or otherwise adjustable so you can tweak the tunings once the box is playing.

[carlife]

Wow, that is some good information! That does make a lot of sense. The only thing I didn't understand (or figure out) is where you got the BP6 3 cu ft rear chamber and the 1.25 cu ft front chamber figures from? I don't think you just guessed on the sizes did you? And I believe you have to tell WINISD the volume figures?

Thanks again.

[Triticum Agricolam]

To get those chamber sizes I just played around with the numbers in WinISD until I got the frequency response I was looking for.

Generally speaking you want your chamber tunings to be about an octave apart. 28 and 55 hz usually seem to work out well. The rear chamber is always going to be a lot bigger than the front chamber. For a starting point for the rear chamber you can use the largest recommended ported box size from the manufacturer and then adjust from there. The front chamber is then set to give fair flat frequency response.

[carlife]

Thanks for the great information. That gives me a good starting point. I will try and post up what I build.

[Smoove]

To get those chamber sizes I just played around with the numbers in WinISD until I got the frequency response I was looking for.

Generally speaking you want your chamber tunings to be about an octave apart. 28 and 55 hz usually seem to work out well. The rear chamber is always going to be a lot bigger than the front chamber. For a starting point for the rear chamber you can use the largest recommended ported box size from the manufacturer and then adjust from there. The front chamber is then set to give fair flat frequency response.

I have seen several where the rear chamber is smaller .

How does that effect things?

[Triticum Agricolam]

I have seen several where the rear chamber is smaller .

How does that effect things?

Were they parallel-tuned or series-tuned boxes? With a series-tuned box its not uncommon to have a smaller rear chamber. With a parallel-tuned box have a smaller low-tuned chamber is going to result in a huge peak in output around the higher tuned chamber's tuning frequency.

Here is an example of what I'm talking about:

The yellow line is the BP6 box from my previous example, but with the chamber sizes flipped so the rear chamber is 1.25 cu and the front chamber is 3 cu ft. You can see the big peak in output centered around 55 Hz.

[Smoove]

I'm guessing the blue line is the rear chamber.

My box will be 6' rear 28hz and 9' front 55hz.
So from what the graph is showing. I wont be burping at 40hz anymore with the new box?