Dual chamber bass reflex design

[Reid Malenfant]

I said i'd get this up for Steve (activexp) but feel free to make use of this if you happen to want to try it out

First up lets get a full sized standard bass reflex enclose design on here, here we go Martin (macca) might be interested in this as i happened to use the Eminence LAB12 bass driver to model it on..



That is about as flat & deep as you can go with no boosting via an electronic network, the slight rise in output near 100Hz is due to voicecoil inductance but 0.5Db isn't really noticeable.

The important thing is we have the enclosure volume (140L) & a tuning frequency (21.9Hz). Just remember that any volume taken up by the driver & the port will mean you need to make the enclosure slightly bigger to keep that 140L! That is a classic single chamber reflex, now comes the fun bit

So you want to damp the driver over a much wider band rather than have it flapping away like a goodun at 40Hz What you need is a double chamber reflex & here is how to build & tune it.

First of all work out 140L divided by 3 = 46.6666L, now double that = 93.3333L. You have now divided the whole enclosure into thirds!

The bass driver needs to be mounted in the 93.333L section of enclosure or if you like the 2/3 of the original, so put a complete baffle accross so that the bottom chamber of the enclosure is isolated. Now this might seem too simple but this is all there is to it! What you now need to do is tune that 93.3333L to the original tuning frequency of 21.9Hz ported to the outside world, i'd suggest on the front baffle, you'll find out why shortly.

Having done that you now have the diameter of the port & it's length is also known. Now comes the easy bit Cut two more ports of exactly the same dimensions & place one of them going from the primary 93.3333L enclosure to the 46.6666L enclosure & the other from the 46.6666L enclosure to the outside world...

You now have a properly tuned double chamber reflex that will damp the driver over nearly two octaves of bandwidth Just make sure that any volume taken up by the driver & the ports will mean you need to make the enclosure slightly bigger to keep that 140L! Or as the case is now 93.3333L & 46.6666L

It's best to port the primary enclosure out the front as this will be radiating (in this enclosures case) @ about 44Hz & above up to nearly 80Hz. as the frequency drops both the primary & secondary chamber ports will begin both radiating until at 21.9Hz they be radiating evenly...


Hope that helps someone

[aquapiranha]

Mark, is that boxcalc you are using there? Do you have any other recommendtions for software?

Ta! Steve

[Reid Malenfant]

Hi Steve, no, it's winISD pro version, great bit of kit it is to. Saves me hours upon hours of calculator use

The best things in life are free

I couldn't explain all that this program is capable of, you name it & it does it just about sums it up

[aquapiranha]

Thanks Mark, I will check it out, I hope it works OK on W7.

Steve

[Reid Malenfant]

You can only try Steve, must admit i'm still using XPpro Nothing will get me to shift either

[aquapiranha]

Well I have installed it but get an error when trying to exit the prog. I will have a look later thanks, Steve

[Reid Malenfant]

Ah crap, i guess this is why i'm still old school operating system

[aquapiranha]

You are right of course, XP is fine for most people. I have used Linux too in the past and that is great except for some compatibility issues. I have a laptop here that I may just put XP on for running these old progs as the laptop is past its best anyway!

[Reid Malenfant]

It'll run fine on XP, whether it be home or pro versions I'd download it to that Steve & then have fun

[activexp]

That's a very interesting design you've got there Mark, can't say I've ever seen anything like it before with 2 external ports and the driver in the larger of the two chambers. Have you got any pics or drawings of it?

I've got WinISD Pro so I'll give it go using your formula.

My DBR is somewhat conventional and influenced by published designs from Fostex.