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-   -   Turning BIB 90 degrees (http://www.diyaudio.com/forums/full-range/226816-turning-bib-90-degrees.html)

AJ 1st January 2013 04:58 PM

Turning BIB 90 degrees
 
I've been looking into running an FX200 in a BIB in a small (already crowded) room. The most I want to deal with is an 18 inch depth and these really need 26-27 inches. The BIB has become a BAB (Big A$$ Box). :D

I sketched up the boxes and started looking at maybe turning them 90 degrees and mounting the drivers on the long side of the box. This would keep the depth down to 18 inches, but possibly with some new problems getting them to act right. My first thought was to mount them outboard of the original baffle location in a (ambiguous) compression chamber like the drawing below. It would obviously create some kind of filter chamber, but other than trial-error experimenting, I'm way out of my league here. :)

http://www.lakerfly.com/images/fx200-2.jpg

Then I looked at mounting the drivers directly into the line at the same location and I'm a little more comfortable trying this approach. I suspect it'll need some pretty aggressive dampening on the back panel directly behind the driver, but other than that, do you guys see any major problems with this? I'd need to relieve the side of the baffle, but it would be minimal, and even less than I've sketched it in here.

http://www.lakerfly.com/images/fx200-6.jpg

http://www.lakerfly.com/images/fx200-7.jpg

http://www.lakerfly.com/images/fx200-8.jpg

If you have any experience doing this or any thoughts, I'd appreciate the input. Thanks.

Allan

xrk971 1st January 2013 06:08 PM

What about making the bumpout internal on divider wall? Probably won't affect performance too much. Keeps box exterior rectangular.

AJ 1st January 2013 07:16 PM

Quote:

Originally Posted by xrk971 (Post 3306923)
What about making the bumpout internal on divider wall? Probably won't affect performance too much. Keeps box exterior rectangular.

You might be on to something there. I took a closer look at the drivers, and there's a good chance it'll fit with no changes at all. The basket starts to taper about 5/16" from the back of the flange, less than half way thru a single sheet of 3/4" baffle. It would probably clear both the baffle and the divider, if I were careful about the placement. Worst case would be some small dimples in either or both.

http://www.lakerfly.com/images/relief.jpg


Allan

xrk971 1st January 2013 07:29 PM

Another option is adjust location of driver vertically until it clears, again, if you don't stray too far, it's probably ok. The effect would be easy to model in HornResp. And in fact, I think the ideal location is really 1/3 the distance from the closed end. It will put location of driver lower and that may not be ideal as it is lower than ear level when sitting.

AJ 1st January 2013 07:45 PM

The cabs will be 84" tall and I've already squeaked the driver down a bit. I should be seeing about 48" from the floor so it'll be above ear height. I don't mind being a little off-axis with Fostex drivers. :)

Allan

Godzilla 2nd January 2013 05:51 PM

I would just move the internal panel over an inch or two at the top and call it a day.

Zilla

AJ 2nd January 2013 06:33 PM

Quote:

Originally Posted by Godzilla (Post 3308208)
I would just move the internal panel over an inch or two at the top and call it a day.

Zilla

:) I like it! I can spin the drivers 45 degrees to a diamond look and completely miss the baffle and divider. No sweat.

Allan

gafhenderson 2nd January 2013 08:10 PM

Quote:

Originally Posted by Godzilla (Post 3308208)
I would just move the internal panel over an inch or two at the top and call it a day.

Zilla

That will make a massive change in response, as it changes the cross sectional area of the closed end by a pretty significant amount, won't it?

xrk971 2nd January 2013 10:32 PM

This should be simulated first and that should set any fears to rest. My gut feeling is that it won't change much if divider is rotated with axis of rotation at edge on top, within reason maybe 2 or 3 degrees to make just enough room.

GM 3rd January 2013 02:24 PM

Quote:

Originally Posted by gafhenderson (Post 3308415)
That will make a massive change in response, as it changes the cross sectional area of the closed end by a pretty significant amount, won't it?

Right, in theory this will cause an increasingly broadband [decreasing Q] mid-bass suck out if the driver isn't shifted downward with decreasing taper [increasing 'throat' area at the closed end].

FWIW, when this situation came up with the original BIB builds, I theorized that just notching out the divider baffle as much as required and covering it with a scrap piece on the backside since the volume around the driver will be sufficiently stuffed to audibly negate any discontinuity in the expansion and on the backside the expansion has slowed/expanded so much that any effect it may have is to further attenuate any unwanted HF.

The main thing is to create enough of a clearance to not constrict the expansion much since it will create a band stop filter, adding an unwanted notch somewhere in the response.

I don't recall any negative responses WRT performance that could be attributed to this, so lacking any proof to the contrary; it's what I would do.

GM


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