Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 112 - diyAudio
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Old 13th August 2006, 02:38 PM   #1111
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Nope, I did mean up the front of the sloping internal baffle, and the front of the rear baffle.

If your enclosures are half as well-built as I suspect Dan, I'm not surprised you don't fancy opening them up -especially the way you use them too, where it likely wouldn't make much of a difference.

I reckon this will work at it's best with the smaller drivers, which obviously have more of a problem in this respect than the larger ones, but it was a big step forward with my boxes. 3mm is the stuff to use. One of those occasions where you don't know you have a problem until it's gone, and you wonder just how you lived with it before. Just to reitterate what Dan mentioned though: please, please make sure you have that floor layer of stuffing or foam guys: it makes a big difference.

My impression is that the cork is particularly good at eating any remaining HF leakage, and of killing reflections inside the horn. Most of us use something directly behind the driver, but this seems to work better, to my ears at least, probably due to the greater coverage preventing off-axis reflections through the driver cone for example. Cheap and easy, and plenty of room to experiment! I might try some on a side wall, and on the rear of the internal baffle as well, out of interest.
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Old 13th August 2006, 02:53 PM   #1112
GM is offline GM  United States
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Greets!

You can post pics via Image Venue which has a resizing feature for images <1.5 mb, or for sites that allow posting from your computer, Snagit 5 allows you to screen capture and save it to a folder in a much smaller file size.

http://www.imagevenue.com/

http://www.addget.com/technote/main....me=snagit5.exe

GM
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Old 13th August 2006, 02:55 PM   #1113
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Useful tips -thanks Greg.

Any ideas re the cork BTW? I seem to remember you like lining parts of your MLTLs, so do you reckon I could be seeing a similar (milder!) effect here?
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Old 13th August 2006, 04:05 PM   #1114
GM is offline GM  United States
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Greets!

You're welcome!

'Thin' acoustic rated cork (0.5 - 0.875" thick) typically has a peak in its noise reduction response curve centered in the upper mids/lower treble with a lower Q (wider BW) up to a point of diminishing returns with increasing thickness. Really thin cork such as drawer liner only damps upper treble BW, which is high enough to get attenuated in the pipe folds if no reflectors are used, so it seems to me that covering large areas such as the angled baffle board with it would mainly damp the spurious panel resonances that strong pipe action can generate.

Anyway, IMO parallel surfaces and low incident angles are the main problems in a BIB, so lining one wall all the way through the bends and on the bottom with whatever density material that doesn't overdamp the transients (dynamics) is what I've done, then adjust in-room pipe Q with stuffing at the point. Never having used cork inside a speaker though, I don't know how it 'sounds' compared to the various felt/fiberglass densities I've used, only that it can work well on its exterior and room first reflections if the decor (SAF) allows it.

GM
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Old 13th August 2006, 07:14 PM   #1115
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Interesting. Useful information, and, as always, many thanks for the input Greg. I might try experimenting a bit more as I've plenty of the stuff lying around.
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Old 13th August 2006, 08:33 PM   #1116
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Is anyone reading this thread considering building the Jumbo GM Hempsters? If so, if this accelerates your decision making process, I just added phase plugs to the Hemp 8.0 V.20 drivers last night and can tell you they became a whole nother animal, with the usual spectacular improvements in treble dispersion, beaming, etc.

These are ValueKing drivers at least on the level of the Visaton B200. I love that big BIB. Or, perhaps, BAB. Bad-A$$ BIB.
Someone please build one. Not me, I'm on Project Lockdown presently.
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Old 13th August 2006, 09:59 PM   #1117
Jim G is offline Jim G  Canada
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Default Jumbo GM hempsters

Hi, I couldn't get the jumbos past my wife but built the smaller 200 sq. inch mouth model on the BIB site. They are in (near) corners. I also have the Visaton B200 on open baffle. My wife and I both much prefer the BIB Hemp8.0 and this is primarily because of the mid range. These are incredible in the bass dept. as well. The hemp driver is really something special. Better in my opinion than the Visiton B200. When my wife first saw these she had no enthusiasm at all. After the 1st couple hrs of listening she said we have to keep these. I don't have pics ( just as well -Haven't veneered or otherwise prettied them yet) Jim G

P.S. I have been thinking about phase plug too (sometning I usually do) Thanks for the recommendation.
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Old 13th August 2006, 10:41 PM   #1118
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JimG

Thanks for that, it never occurred to me to sell the idea of the 200^2" job. Did you use Scott's DIM's or your own? More info please, as possibly I could take another swipe at the idea armed with scissors and cardboard, and make another 'sales' presentation...

Glad you like the Hempsters. I also prefer them to the B200, which sound too hi fi in comparison, IMHO, the warmth of the midrange, especially the lower midband right down to 200Hz is to die for in my book. It combines warmth, with resolution, and TONE is out the window. And now someone whom has built some Hemp BIB's.
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Old 13th August 2006, 11:22 PM   #1119
Jim G is offline Jim G  Canada
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Hi, I used Scott's DIMS. sim for this one and sim for GM's are there to be compared. I was surprised at how well these image and as has been said before there is some similarity to OB sound. Maybe because of being spread over the ceiling and off the walls. Jim G
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Old 13th August 2006, 11:35 PM   #1120
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Another one falls prey! And if 'she who must be obeyed' likes them too, bonus! (big bonus). Hemp FR8 BIBs. I would like to hear those.

Dan -judging from the responses in MathCad at least, I don't think there's going to be a massive difference between the Monolith and the 200in^2 version, providing you can corner load them (not that I need to tell you that). Although the curve looks like it rolls off more than some others at first glance, check out the SPL levels at 30Hz: 91db. And that's before you factor in room-gain. Gulp. By contrast, the FE168ESigma is 82db at 30Hz.
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