Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 513 - diyAudio
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Old 24th January 2013, 08:29 PM   #5121
Squeak is offline Squeak  Denmark
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Exactly, the two mouths become one and the waves combine.
Some old horns with this construction also make the divider slightly asymmetric to combat ribbling and avoid too much stuffing to do the job.

It won't completely solve the problem of space because the basic geometric problem is the same no matter how much you slice the space. But it will allow for more flexibility on the placement and shape of the divider since now it doesn't rely on the frame.
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Old 24th January 2013, 09:04 PM   #5122
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Yes, xrk, I'm talking about the FIB.
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Old 25th January 2013, 12:06 AM   #5123
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OK, so I am torn. Should I build the FIB as I have drawn it above or with the inverted "V" in the middle like below? I think if I stick with the one as drawn (single diagonal) it will have more of a chance of sounding like what I expect a BIB to sound like. Going with two horn mouths could result in something totally different.
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Last edited by xrk971; 25th January 2013 at 12:16 AM.
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Old 25th January 2013, 12:39 AM   #5124
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Quote:
Originally Posted by Squeak View Post
xrk971, I know you love your curves, and with the high Qts of the Vifa driver it might work fine, but for drivers with lower values it might not.

You are after all starting with a clearly parabolic horn going into an exponential-ish, it's almost an MLTQWT with a horn on the mouth.

Why not just make a V shaped divider, that would also take care of a lot of the bracing?
Squeak,

That is a mouthful... MLTQWT... mass loaded tapered quarter wave tube? How is it mass loaded - there is no constriction on the mouth? I think the slight exponential mouth will enhance the performance if anything. Not sure why this is limited to low Qts drivers - as long as you use the BIB calculator, which, IIRC relies on the magic alignment formula that GM came up with: BIB volume is proportional to Vas*Qts^1.2.
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Old 25th January 2013, 09:43 AM   #5125
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Well maybe the ML part was overdoing it. :-) The point was that it starts of with expanding less and less. Essentially something like a transmission line with only a little hornloading, which is good for high Qts drivers but not for something like FE126. Then it goes into an almost straight section with a turn and expands into a horn.

Have you considered not folding it? If you have reasonably tall ceilings you will get the mouth closer to them. You will also get a different, perhaps more elegant visual impression that way.
If you make them a long wedge, and you put the driver on the flat side you'll have the driver pointing slightly down, which is perhaps not a bad thing if you put them a bit above ear level.
If you put them on the other pointed side you'll run into the same problem of space that you solved by curving the divider. You could also solve it, again i guess more elegantly, by squashing/flattening the wedge more than 4 inches to make it wider.
Then you'd of course have to make sure that the magnet doesn't create a choke point. Perhaps by making the whole, or part of the front baffle thicker.
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Old 25th January 2013, 10:30 AM   #5126
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With regards to the difference between the two different folded versions, I can't see why it wouldn't be minimal. The openings point the same way and each carry the exactly half the wave.
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Old 25th January 2013, 08:49 PM   #5127
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Squeek,
Interesting thoughts about unfolded BIB - kind of like upside down Voigt pipe without mass loading. could be interesting visually and I like idea of pointing driver down. However, it becomes too imposing and WAF goes down. The V in the middle, if it splits the mouth, the circumference of the horn is cut in half and this is what affects the ultimate low freq. That is why I wanted the horns to combine and form same circumference again.
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Old 25th January 2013, 10:52 PM   #5128
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There will be virtually no difference whether the two wavefronts combine shortly before exiting the cab or just outside it.

About WAF: If the wife has the last word, I'm not so sure she wouldn't be more inclined towards longer more slender cabs, rather than having two of the monolith from 2001 a Space Odyssey on the wall? And If the former gives better bass and is easier to build (no extra braces and bending), then why not?
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Old 25th January 2013, 11:07 PM   #5129
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The long ones require joining two sheets of foam core as max length is 30 in. If I made it in plywood or masonite then no problem. Not sure if the single long one would sound better. The fold allows one to put stuffing at the turn to absorb some of the higher frequencies and the corners act as naturnal low pass filters.
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Old 26th January 2013, 12:11 AM   #5130
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The long one would be just as easy to stuff if you put an X of string in the pipe to keep the stuffing from sliding down.
True, the corners will to some small degree work as filters, but you will also gain some efficiency with the straight pipe. You'll be able to better fine tune and balance between efficiency and HF output with stuffing alone.

You'll need exactly the same amount of baffle material for both approaches. Just cut the sheet into two strips and make sure the seam is airtight.
Clad the whole thing in wallpaper for a fast and wife friendly finish.

Last edited by Squeak; 26th January 2013 at 12:14 AM.
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