Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 511 - diyAudio
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Old 23rd January 2013, 02:16 AM   #5101
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Default A lucky break!

While waiting to build one of the more popular boxes for the Alpair 7.3, I stuck it into a BIB that I had built for the fostex fe126 many years ago and had abandoned. What luck! In the 6 months or so I have had them they have blossomed into a delightful set of speakers.
One of the problems I had earlier with the fe126 was that I had to stuff it lightly to get any decent bass out of it. Which also resulted in quite a bit of the mid frequencies coming out of the mouth killing all imaging and soundstage. Because of the Alpair's built in baffle step I am able to stuff it well and still get great bass.
So if any of you have this BIB and are in the mood for some speaker rolling, try this and you wont be disappointed. Just remember that the Alpair's require a gradual and gentle break in. So give it a month or two. Also despite its specs it is a very efficient speaker. I am driving it with an SE2A3(3-4 watts).
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Old 23rd January 2013, 06:27 AM   #5102
xrk971 is online now xrk971  United States
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Default Can a "Flat" BIB work?

I was wondering if the BIB can be "squashed" flat, preserving the cross sectional area but making the aspect ratio a flat box with the driver mounted on the flat side so that the BIB can be mounted on a wall like a painting? For example, the driver I intend to use will produce a BIB with cross sectional area of about 48 sq inches based on 6 in wide x 8 in deep. Can I make this 4 in wide by 12 in deep (with driver on the long side)? I would imagine that it might change the "character" of the BIB sound. Nonetheless, I am thinking of trying it out quickly in foam core.

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Old 23rd January 2013, 03:12 PM   #5103
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If you do this make sure you have enough room behind the driver.

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Old 23rd January 2013, 03:16 PM   #5104
GM is online now GM  United States
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Yes, though the divider board will need to be offset between the sides to ensure it doesn't create a choke point, ergo maybe longer or shorter, but don't know of a rule-of-thumb or easy math to calculate it, so a bit of scale modeling/folding with heavy paper is what I do.

GM
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Old 23rd January 2013, 04:08 PM   #5105
Squeak is offline Squeak  Denmark
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You could straighten the BiB out to get the mouth closer to the ceiling if the specs permit. Otherwise you will probably have to split the divider board into a v shape (seen from the front) or alternatively shift the driver to one side.
The usual configuration will not work with a very squashed BiB, since the hornloading will be minimal and closer to parabolical. You'll end up with with a transmisson line instead of a horn.

Last edited by Squeak; 23rd January 2013 at 04:19 PM.
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Old 23rd January 2013, 04:28 PM   #5106
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All pipe horns with one set of parallel walls are parabolic, so a folded one with a straight divider[s] is a series of parabolic expansions, hence the need to tune it at least an octave below whatever the desired LF corner is.

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Old 23rd January 2013, 06:01 PM   #5107
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Quote:
Originally Posted by xrk971 View Post
I was wondering if the BIB can be "squashed" flat, preserving the cross sectional area but making the aspect ratio a flat box with the driver mounted on the flat side so that the BIB can be mounted on a wall like a painting? For example, the driver I intend to use will produce a BIB with cross sectional area of about 48 sq inches based on 6 in wide x 8 in deep. Can I make this 4 in wide by 12 in deep (with driver on the long side)? I would imagine that it might change the "character" of the BIB sound. Nonetheless, I am thinking of trying it out quickly in foam core.
Must be reading my mind. I was staring at the wall last night thinking this exact thought. Time was not permitting me to start my Cornu project. However, as I was looking through a notebook, I found plans that were drawn up to try to build a BIB into a wall. Basically it was a BIB with the driver moved to the side.

So enough rambling, what I imagined was a wall mounted BIB that had the paths split so one would fire up and the other down. This may or may not work. Was going to try to draw it up later. The big issue I saw was the size of the units. Most BIBs are large. A box that is quarter length may work better than the half wave monster.

Is this a bad idea in anyone's mind?
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Old 23rd January 2013, 08:21 PM   #5108
B00B00 is offline B00B00  Canada
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Hello one and all... I've been reading steadily for the last month and am at page 311 and going strong. I have decided to build a set of BIBs. I have a set of Fostex FE206en breaking in as we speak and have sourced some 100 year old barn lumber (spruce) for the front of the speakers.
1 inch thick, once sanded and finished, it should have a nice patina I would think.

I'm Going to build the sides out of 1inch plywood and the slant bottom and rear out of presswood or particleboard. (In this case it will mean I can buy one sheet of one inch plywood and one of half inch particleboard (which the pieces will be doubled up and glued together)

The dimensions from the excel Bib calculator give me 10*13*87inches w*d*h

Are these still accurate or have more recent builds pointed towards different dimensions?

I haven't decided what to do with the supra-baffle as of yet. I might make one a la frugalhorn or see if I can turn something on a lathe.

My two main concerns are:
Do my dimensions sound correct?
And is the use of particleboard optimal for the slant, bottom and back?
(I've read differing opinions as to if the back should or not be built with particleboard)

Thank you,
-andre-
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Old 23rd January 2013, 09:14 PM   #5109
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by GM View Post
Yes, though the divider board will need to be offset between the sides to ensure it doesn't create a choke point, ergo maybe longer or shorter, but don't know of a rule-of-thumb or easy math to calculate it, so a bit of scale modeling/folding with heavy paper is what I do.

GM
I was thinking of slightly curving the divider to bow concave on driver side to make room, and bow convex on horn mouth side which makes it kind of exponential horn. Easy to curve with foam core. How does this affect tuning? Do I need to run sim in Hornresp or just go for it?
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Old 24th January 2013, 03:41 AM   #5110
GM is online now GM  United States
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Quote:
Originally Posted by B00B00 View Post
The dimensions from the excel Bib calculator give me 10*13*87inches w*d*h

My two main concerns are:
Do my dimensions sound correct?
And is the use of particleboard optimal for the slant, bottom and back?
(I've read differing opinions as to if the back should or not be built with particleboard)
Greets!

Agreed, I’ve built, or at least ‘skinned’, numerous speakers with planks from a very old barn and once finished off can be quite stunning, whether rustic or planed to expose its inner beauty.

Hmm, the only specs I have are the published ones, which = 75.24” H, x 9.982” W x 14.117” D [inside].

45 Hz Fs
2.51 ft^3 Vas
0.1864 Qts

So, what specs are you using?

Also, are you going to use a high output impedance amp? If so, need to know how much since it will increase Qts.

FWIW, it takes at least 1.125” thick MDF to ~match 19 mm Baltic Birch or similar plywood’s stiffness, so probably 2-4x that with cheap pressboard.

For the bottom then, 1” pressboard is OK since the weight of the cab will mass load it to the floor, but the internal baffle board would need to be braced to both opposing walls with an offset vertical divider, which will of course stiffen up the pressboard rear panel also.

Anyway, you can build speakers out of most anything, but in most cases it’s all about getting the cab’s Fs either above or below the speaker’s intended pass-band, so below ~200-300 Hz it’s usually easier/cheaper to make the cab more rigid to push its Fs higher than making it massive enough to push it below the pass-band.

Bracing increases stiffness quicker than by adding mass, so when in doubt about a panel’s stiffness, just add [more] bracing.

GM
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