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Old 27th June 2009, 12:23 AM   #1
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Join Date: May 2009
Default When is a liter not a liter? The shape of things to come.

The double base reflex enclosure published by Fostex for the FE127e is a tall rectangular cabinet. If the volumes were the same for both the chambers, and the vents were all the same, etc., how would it change the driver's performance to use a tube cabinet of similar stature?

There are two issues that seem to interact as I think about it. One is the issue of front baffle and I know people go round and round on this. But I have not seen a discussion of the internal dynamics. Is it just an issue of volume and the spring it creates or does the shape of the first chamber and placement of the vent make for a different spring or harmonics than a cylindrical chamber with the port in the center, for instance? Will the first port remain tuned to (FB) 120Hz and the second to 53Hz?

I wanted to do something different and I like the looks of a tall floor standing cylinder in the placement I am thinking of. It would be a piece of cake to take a 6" PVC and fashion this puppy. Relatively cheap and almost no dust!

Anyone have experience with this or can anticipate the results?

Thanking all in advance.

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Old 27th June 2009, 12:52 AM   #2
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Join Date: Jan 2007
Hi Bruce, from what I've read, nobody has been too impressed with Fostex double-bass reflex cabs.

The gurus here will tell you that as a BR becomes tall and skinny, it transitions into a quarter-wave resonator a.k.a transmission line (TL). So it's not just a question of the Helmholz resonance (a function of the cab's volume) and it becomes a function of the height.

But PVC is a definitely cool way to go. You might find this of interest: http://www.t-linespeakers.org/projec...son/index.html
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Old 27th June 2009, 03:35 AM   #3
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You're essentially correct. The ports net different tunings. The gain of such a design is decreased excursion compared to a single reflex design. I have no experience with this driver but the DCR I built for the CHR70 works great, but I used 3 ports and the driver chamber is twice the volume of the second chamber.
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