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Old 11th September 2007, 06:03 AM   #1
GratefulTony is offline GratefulTony  United States
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Join Date: Sep 2007
Default BIB doublefold

Hi everybody... long time reader, first time poster...
There really is a lot of information on these forums, and I have learned a lot!

I have a newbie question regarding the "bigger is better" cabinet design.
As I understand, the BIB is some sort of a transmission line, or a giant folded voight pipe (or something). Generally speaking, is it of the overall consensus that adding folds to the resonant chamber greatly decrease performance? I know there are already a lot of different horn designs out there, but has anyone heard of a re-folded Bib? (or maybe it has a different name)
Perhaps with 2 reversals rather than 1?
(reducing the height 33% or so, but increasing the depth (or width?))
(I know... BIGGER is in the name... but do they really need to be so... big?)
I have heard different things from different sources: some claim that adding folds to a (tqwt) for instance will only slightly alter performance, while others claim that this will make the response a lot less even. Im sure the truth lies somewhere between these extremes, but how serious is it realistically?
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Old 11th September 2007, 11:50 AM   #2
Scottmoose is offline Scottmoose  United Kingdom
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Join Date: Mar 2005
Location: UK
The BIB is a back loaded horn (chamberless pipe-horn to be exact). Yes, it really does need to be that big. That's the way it works -the room completes the expansion of the horn -it needs to couple to the room to work properly. So long as you got the vent low-down & near a wall with a twin fold, it should do OK. I wouldn't recommend a short upward venting type. It won't couple to the room anything like as effectively, and the driver position will be pretty low. Personally, I like the height -adds a bit of character & it's certainly different to the average box.

Adding folds to a horn does a couple of things. Folds are the enemy of efficiency, but in a sense that can be used to the designer's purposes. HF, with it's short wavelength, hates folds. As the BIB has no filter chamber, the fold helps attenuate some of the unwanted mids from coming out of the terminus. The LF we want, OTOH, with its longer wavelength, isn't that bothered by a fold, and is preserved.

I did a twin & a triple fold study for a pipe-horn with Seas co-ax units as a bit of Christmas fun for the lads last year. That unit has a very low Fs (25Hz) though, so the height was preserved.
"'That'll do", comes the cry of the perfectionist down the ages.' James May -The Reassembler
www.wodendesign.com Community sites www.frugal-horn.com http://frugal-phile.com/
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