Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 516 - diyAudio
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Old 27th January 2013, 08:25 PM   #5151
xrk971 is offline xrk971  United States
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Kec,
The external dimensions are 27 in tall, 16 in wide, 3 in deep. Thickness of material is 3/16 in. The divider is an inverted V (mildly curved to make room for driver) and V comes down to 4 in from bottom so that 8 in x 3 in cross sectional area is preserved. V is laterally offset so that top of (vertex) is 2 in to the side of centerline. Driver is located 10.75 in from top edge. I offset V to reduce phase interference from centrally located driver and to reduce possible phase cancellation issues from two identical mouths combining at top. The curve in the V divider is such that an additional 3/8 in on each side of V is provided to original space next to driver location. Hope that helps.

Last edited by xrk971; 27th January 2013 at 08:32 PM.
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Old 27th January 2013, 09:00 PM   #5152
xrk971 is offline xrk971  United States
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Default FIB as built

As built dimensions in inches.
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Old 27th January 2013, 09:15 PM   #5153
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Man xr, you are quick. You are my hero
Thanks.
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Old 27th January 2013, 09:19 PM   #5154
kec is offline kec  United States
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Xr,

Isn't the depth 3"?
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Old 27th January 2013, 09:39 PM   #5155
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by kec View Post
Xr,

Isn't the depth 3"?
Sorry, my blunder. 3 inch depth is correct. I just mounted it on wall and hooked it up to a real amp (45 w/ch ) and this thing rocks! It is very loud and moves a lot of air through the mouth. Great bass that fills room. Very nice
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Old 27th January 2013, 10:06 PM   #5156
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Quote:
Originally Posted by Squeak View Post
Just a little OT question: When you talk about protecting the driver in this way, as you often do, you don't mean the resistive pressure actually stopping the driver from moving?
Rather you're saying that you don't have to EQ it so much to get the same bass, and thereby protecting the driver from over-excursion at peaks?
Am I right?
What I mean is that the horn's air 'plug' has mass, so it mass loads the driver, lowering its effective Fs, Fp. The extra acoustic efficiency is due to confining the output over a narrower arc same as any horn.

Since the BIB is normally tuned an octave below driver Fs combined with the simple math used to determine its net Vb, its effective Fs/Fp will theoretically be a 1/2 octave lower [~0.707x Fs] in 2pi [1/2] space.

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Old 28th January 2013, 12:35 AM   #5157
xrk971 is offline xrk971  United States
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Ok, so if I were to measure the horn output, expect peak freq to be about 88 Hz for the 125 Hz fs of the TC9FD. If one were to restrict the horn mouth, would it drive the freq lower at the expense of output? Kind of like mass loading.
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Old 28th January 2013, 03:49 AM   #5158
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If by 'peak' you mean the pipe's resonant frequency, then yes, if you used the BIB calculator to design it and the driver's measured Fs is fairly close.

It would shift it down some if you really restricted it, but at the expense of bass output higher up, which might be a good thing if it has an overpowering mid-bass unless heavily stuffed.

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Old 28th January 2013, 08:57 AM   #5159
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How much stuffing is usually required and where do you put it? I have the section under the driver loosely stuffed and notice a big bump at circa 200 Hz, maybe corresponding to the 16 in wide half-wave mode? I think that is what it is because it is shifted slightly depending on whether I measure the small or big mouth's output. It is huge, 10 to 15 dB above rest of bass platform. I am getting bass down to about 70 Hz so maybe combo of stuffing bottom and adding constrictor at top?
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Old 28th January 2013, 10:38 AM   #5160
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Quote:
Originally Posted by GM View Post
What I mean is that the horn's air 'plug' has mass, so it mass loads the driver, lowering its effective Fs, Fp. The extra acoustic efficiency is due to confining the output over a narrower arc same as any horn.

Since the BIB is normally tuned an octave below driver Fs combined with the simple math used to determine its net Vb, its effective Fs/Fp will theoretically be a 1/2 octave lower [~0.707x Fs] in 2pi [1/2] space.

GM
Ok. I just don't understand what that has to do with the boundary loading you were talking about in your post. Surely something that is outside the mouth of the horn (or indeed the loading chamber or immediate throat section of the horn) can't have much effect on lovering the Fs of the driver?
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