exact dimensions of a BIB fe167e - diyAudio
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Old 20th January 2007, 04:07 PM   #1
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Default exact dimensions of a BIB fe167e

ok... i want to build a BIB fe167e.

I do have the link to the general position where the driver needs to be mounted and length of the line.

question is how wide and deep and high should the enclosure be???

also... do i need a baffle step filter on these?

basic questions i know.

finally, what thickness and type of wood should i use?

any stuffing?

Thank!!
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Old 20th January 2007, 04:37 PM   #2
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Rich, are you familiar with Godzilla's BIB page?

http://www.zillaspeak.com/bib-howtobuild.asp

I think for the driver you mentioned you're going to be around 68" tall, and 8" wide by 12" deep ID. This assumes 3/4" material.

Scott, MG, and the others can tell ya for sure but I think those are your dimensions.

Rick
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Old 21st January 2007, 12:51 AM   #3
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I have the same driver and was thinking about maybe building this also. With L=136", Z=27.5" and Sm=87.75^2" from Zilla's page, I came up with the final length of 68" and 8"x11" (WxD) for the internal dimensions. External dimensions will be a bit bigger due to the wood thickness. The internal baffle length will be determined by mid points near the bottom as explained in the web page.

I think it would be helpful if Zilla's page should how to calculate the width and depth. IIRC the width/depth should equal .707. So in my case 8/11=.727 with Sm=88^2". Close enough, I think...

Also, the length might have to be a bit longer due to the terminus of the internal baffle taking up some line length. Again this is an "I think" assumption.

Hope this helps, or ignore all of this if I am completely off track!

A little help please if I am...
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Old 21st January 2007, 03:40 PM   #4
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That agrees with the recommendation of just using L/2 as the inside height. I worked out the geometry and found that this results in an enclosure that's close, but not quite long enough. I'm not sure if the 'error' is significant...

The approximation made using L/2 is that the path around the fold is equal to D. Making the approximation that the path around the fold is a semicircle (still an approximation, but a better one I think) I find that part of the path to be close to pi*(D+T)/4 where T is the thickness of the sloping divider and D is the inside depth of the cabinet.

The difference between the two approximations is D - pi*(D+T)/4. For D=11 and T=3/4 inches that works out to be a about 1.77 inches.

You also lose a much smaller amount due to the fact that the opening in the top of the cab is horizontal. Looking at a cutaway drawing from the side, draw an imaginary line right up the center of the rear section. To match MJK's model the mouth should be perpendicular to this center line; the back of the BIB should be a little taller than the front. As far as I can tell the tiny bit of difference in length is about D^2/4L.

The little bit of line length that you lose is really small; less than 1/4 inch with D=11 and L=136 and I'm sure it's not worth worrying about on its own. But if we're making corrections we might as well throw it in. In fact, the two corrections add up to almost exactly 2 inches. So, for this particular design, I would make the inside height 1 inch taller than L/2 or 69 inches. (You gain an inch going down the front section and another going back up the rear.)

As for A=B=C=D/2 (see the drawing at http://www.zillaspeak.com/bib-howtobuild.asp) I figure that A should be smaller than B by approximately (pi/4)*(D^2/L). In this case it works out to be about 0.7 inches. That means moving the end of the divider a measly 0.35 (~3/8) inches closer to the front of the cab. C should be about half way in between the two.

Will any of this make a bit of difference to the way the thing sounds? Probably not, but refinements are OK, aren't they?

And, I know that it's irresponsible of me to give these results without showing the derivations, at least so that people can check my math, but that would require me to make nice clear drawings. I'm too lazy on this Sunday morning. I might get around to it if anyone actually cares, and they probably shouldn't as the already recommended approximations (L/2 and A=B=C) are probably more than good enough.

-- Dave
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Old 21st January 2007, 07:27 PM   #5
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so 69" x 8" x 11" ? ID

driver position same as Godzilla pages?
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Old 21st January 2007, 07:30 PM   #6
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what thickness of wood and type of wood recommended?

baltic birch ply?
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Old 21st January 2007, 09:13 PM   #7
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Quote:
Originally posted by AudioGeek
so 69" x 8" x 11" ? ID

driver position same as Godzilla pages?

With 3/4" material the ID should be 11 3/4" to 12" should it not?
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Old 21st January 2007, 09:19 PM   #8
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Default umm...

i thought that 69x8x11 was the inside dimensions... irrelevant of thickness of wood.

soooo... depending on how thick the wood is the OD or outside dimensions would be different.

anyways... where do i find 4x8 sheets of baltic birch plywood?
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Old 21st January 2007, 09:43 PM   #9
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If it were nothing but a box, but it has an extra internal baffle that occupies space. It probably wouldn't be the end of the world if this were ignored but I'm thinking it should be considered. YMMV.

Rick
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Old 21st January 2007, 09:49 PM   #10
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is that to account for the internal baffle 3/4" width at the top of the cabinet?
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