Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 525 - diyAudio
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Old 13th June 2013, 02:45 AM   #5241
GM is offline GM  United States
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It will affect it, but you'll need to sim it in MJK's software to see how it is affected by the room. FWIW, a long time ago, he suggested moving it down to 0.434*L for 'subs', so a position to consider.

Consider too that a max flat alignment for this driver is around a 67.29 Fb, or a ~100" path-length BIB if inputted as Fs, shifting the driver down to ~21.7", so if you can tolerate the extra height and willing to gamble some time/wood...........

GM
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Old 21st June 2013, 12:33 PM   #5242
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Default Model of Generalized BIB with Room Placement

I have a generalized model of a BIB in AkAbak where I just input the Width x Depth x Height and driver T/S parameters and it lets me look at the effect of placement near or away from a wall. As a test case, I tried the Betsy K in a BIB which for some reason, I do not ever recall anyone trying out. If you have measurements to compare that would be great.

The simulations are with the BIB mounted flush against a wall with mic at 1 m (first plot), then 5 m away (second plot). Now place the BIB 60 in away from a back wall with listening position 5 m away (third plot). Notice that the response is very uneven when not assisted by wall-loading.

If you put the BIB 60 in away from either wall in a corner and stand 5 meters away it helps to restore some of the low end bass extension that was lost from the above case, but you get a response that has holes at 70 Hz and 220 Hz, and general uneven response (fourth plot).

The case of 1 m away flush against a wall looks very good but as one starts to move away from speaker, the response degrades. Nonetheless, the BIB still has a decent response for such a simple design.
Attached Images
File Type: png Betsy-BIB-1m-flush-wall.png (32.7 KB, 231 views)
File Type: png Betsy-BIB-5m-flush-wall.png (33.3 KB, 222 views)
File Type: png Betsy-BIB-5m-60in-wall.png (31.9 KB, 217 views)
File Type: png Betsy-BIB-5m-60in-CORNER-wall.png (35.4 KB, 219 views)
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Old 21st June 2013, 04:22 PM   #5243
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I'd say with a driver with those specs, don't put it on the wall and don't put it in a BIB of any kind.
It looks to be very directive and with a soft top, so unless assisted by a tweeter, you need to toe in.
The Qts is quite high and so is the FS for a driver this size, so I'd say some kind of transmission line would be good. Maybe a big TABAQ?
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Old 21st June 2013, 06:33 PM   #5244
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Hmm, the BIB is a TL, which as you imply is best suited for high Qts drivers, so why the seeming contradiction?

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Old 21st June 2013, 06:38 PM   #5245
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Quote:
Originally Posted by xrk971 View Post
The case of 1 m away flush against a wall looks very good but as one starts to move away from speaker, the response degrades. Nonetheless, the BIB still has a decent response for such a simple design.
From here: A Speaker that Kicks Butt in Large Spaces

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Originally Posted by GM View Post
Hmm, many folk's listening experiences and occasional measurements don't line up hardly at all with these or other long distance sims you've posted, so I'm inclined to ignore all of the room modes BW of those more than a meter away.........

For sure, I wouldn't use them for tweaking a design.

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Old 21st June 2013, 07:02 PM   #5246
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Quote:
Originally Posted by xrk971 View Post
I have a generalized model of a BIB in AkAbak where I just input the Width x Depth x Height and driver T/S parameters and it lets me look at the effect of placement near or away from a wall. As a test case, I tried the Betsy K in a BIB which for some reason, I do not ever recall anyone trying out. If you have measurements to compare that would be great.

The simulations are with the BIB mounted flush against a wall with mic at 1 m (first plot), then 5 m away (second plot). Now place the BIB 60 in away from a back wall with listening position 5 m away (third plot). Notice that the response is very uneven when not assisted by wall-loading.

If you put the BIB 60 in away from either wall in a corner and stand 5 meters away it helps to restore some of the low end bass extension that was lost from the above case, but you get a response that has holes at 70 Hz and 220 Hz, and general uneven response (fourth plot).

The case of 1 m away flush against a wall looks very good but as one starts to move away from speaker, the response degrades. Nonetheless, the BIB still has a decent response for such a simple design.
Is that taking into account the ceiling with the BIB, when away from the wall?
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Old 21st June 2013, 07:16 PM   #5247
Squeak is offline Squeak  Denmark
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Quote:
Originally Posted by GM View Post
Hmm, the BIB is a TL, which as you imply is best suited for high Qts drivers, so why the seeming contradiction?

GM
It's a horn! ;-) Of course almost everything in audio is rather fluid, but I'd say that a BiB is mostly a horn. Why else would all those low Qts Fostex drivers work so well in them? It's expanding and has compression in the throat area. In my book that makes it a tapped horn.
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Old 21st June 2013, 07:23 PM   #5248
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Quote:
Originally Posted by gafhenderson View Post
Is that taking into account the ceiling with the BIB, when away from the wall?
I don't have a way to simulate a ceiling unless the the floor is left off. There is a way to do a wall and floor or ceiling and floor, or two walls and ceiling in corner. But not a floor and a ceiling far away from walls. So having a ceiling will certainly improve the bass away from walls for a tall BIB.
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Old 21st June 2013, 07:25 PM   #5249
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Quote:
Originally Posted by Squeak View Post
It's a horn! ;-) Of course almost everything in audio is rather fluid, but I'd say that a BiB is mostly a horn. Why else would all those low Qts Fostex drivers work so well in them? It's expanding and has compression in the throat area. In my book that makes it a tapped horn.
In my experience, a BIB works well with low or moderately high circa 0.9 (not super high) Qts drivers. It is almost as universal as an enclosure can get.

A horn is an expanding TL, a restricted terminus horn is a mass loaded tapered TL, there is no distinction in AkAbak - they are all waveguides.
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Old 21st June 2013, 11:14 PM   #5250
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Quote:
Originally Posted by Squeak View Post
It's a horn!
Acoustically, it's a waveguide since it's a parabolic expansion and why pretty much anything works in them, at least in a sim up to a 2.56 Qts, though of course a really high Qts would make it unacceptably large if the BIB calculator is used [~75.13 ft^3 Vs the sim's ~6.13 ft^3].

This one is tuned to ~reactance annul the driver's impedance at Fs [AKA max flat impedance TL].

GM
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