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Old 29th October 2006, 02:43 PM   #1
gychang is offline gychang  United States
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Default BIB with 167E, open top exposed

Due to enthusiasm with the 167E speakers in BIB, I also plan to build my 2nd BIB (just finishing one with a cheapie MCM speaker as a trial) this time with 167E.

According to the BIB site:

L = (Line length) 136in
Zdriver = Driver 27.5" down from sealed end of cabinet
Sm = 87.75in^2

L is to short and will expose the opened top of the cabinet for normal sized adult. Building up the base will make the speaker sit up higher. I don't want to close the top since it may affect sound.

Will elevating the base 5" affect sound? any comments particularly one's who have built the combination will be greatly appreciated.

gychang
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Old 29th October 2006, 03:20 PM   #2
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A simple grill frame with the typical thin material sold for the purpose will not affect the sound. It's a horn terminus -the frequencies coming from it are too low a wavelength to be in the least affected, unless you decide to use a duvet as grill cloth of course.

If you build the base up, make sure the cavity is filled with something solid, and brace it well, or you'll get unwanted resonances creeping in. Remember it might put the driver up a bit high too.
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Old 29th October 2006, 03:40 PM   #3
holdent is offline holdent  Canada
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I was just thinking about building the BIB for the FE167E last night and unfortuantely can't answer your question but have some questions of my own!

For an 8" internal width, the depth is just under 11". I calculate A = B = C to be ~5.5" and the internal height to be ~61.53". The "divider" board should be ~55.8".

I modeled the FE167E BIB also using King's MathCad model and got the same ragged SPL response curve. I understand that these sound much better than they model but am concerned about how ragged it appeared. To "flatten" in the model I added stuffing with increasing densities. Here's 0.125 lbs/ft3:
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Old 29th October 2006, 03:41 PM   #4
holdent is offline holdent  Canada
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Next 0.25 lbs/ft3
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Old 29th October 2006, 03:43 PM   #5
holdent is offline holdent  Canada
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Last at 0.5 lbs/ft3. This is now looking like the response curve for a transmission line.
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Old 29th October 2006, 03:46 PM   #6
holdent is offline holdent  Canada
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Stuffing does "flatten: the peaks and nulls but also rolls off the low end response - probably not a good trade off. It does however greatly improve the impulse response; some maybe it is a good trade off..?

Does anyone have experience with BIB's and stuffing?

Here's the impulse response lightly stuffed (0.125 lbs/ft3):
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Old 29th October 2006, 03:48 PM   #7
holdent is offline holdent  Canada
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And now heavily stuffed (0.5 lbs/ft3):

(The impulse response of an unstuffed BIB is surprisingly bad modeled)
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Old 29th October 2006, 04:24 PM   #8
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Yes. It's all on the thread, though you won't want to wade through all that.

The response you are geting looks the way it does because you're modelling a 1/2 space response. But the BIB is specifically intended for 1/8 space placement (corners). The vent is actually a terminus, not a horn mouth: the room itself completes the flare and forms the mouth. None of this is currently accounted for with Martin's worksheets. This is not me denigrating Martin's work; I'm one of his most vocal supporters, and he's a good friend of mine; I'm just pointing out the current limitation[s] of the software with regard to modelling corner horns. FR, impedence and impulse response are all dramatically smoothed by the correct corner placement. This is why the BIB was ignored for a while; people forgot that this speaker actually uses the room as a continuation of the cabinet, and that they were only modelling part of the resultant system.

Stuffing the BIB is simple enough. The harmonics we want to clobber are best done with about 0.25lbs ft^3 in the point above the driver, some wadding behind the driver to to prevent reflections back through the cone, and a nice thick layer of damping on the cabinet base. That's about it.
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Old 29th October 2006, 05:01 PM   #9
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The BIB does have a ragged response. Its in the physics of Voight type enclosures.
Consider mass loading the port to smooth things out. Thats what I did and am very happy with the result.

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Old 29th October 2006, 05:05 PM   #10
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Agreed and disagreed in equal proportions. It's not LS3/5a monitor flat, but most horns aren't, and it's no worse than others if placed correctly. These traditional P.G.A.H. Voigt chamberless corner-horns operate over a very wide passband, but the ripple this would cause is negated by the room, providing the driver / cabinet are properly matched. Mass loading is a useful tweak, but transforms it into a QWR cabinet rather than a horn. A good move if the driver has characteristics that would render it unsuitable for this loading (e.g. too high a Q or Vas). Are you still running those iosphon (I think?) drivers in yours BTW? Last I recall, one had died. Hope you managed to get them going again -be a crying shame if they had to go off to that great scrap-heap in the sky.
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