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Old 9th October 2006, 12:38 PM   #11
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Well now, a BIB is on the cards. The site is at www.zillaspeak.com/bib.asp for those interested -Jeff (Godzilla) very kindly offered to host & design the pages, and GM has quite a few of his variations of this cabinet there too.

For those who haven't seen the BIB before, it's a traditional P.G.A.H. Voigt style chamberless corner horn that vents upward -the top is left completely open, and that forms the terminus. The horn mouth is actually formed by the 1/8 space loading of the room; the reflectional boundary conditions creating a virtual mouth 8 times larger than the cabinet terminus. The idea dates back to the 1930s -probably to the late '20s so high tech it is not, but it is very effective.

1/2 space MathCad FR graph attached. Word of warning: this is a big cabinet. Very big. As they're intended for corners this makes life easier, but they're still not small. Most of the ripple you see in the response will be killed by the room, leaving them pretty flat BTW (true -just ask any BIB builder). No worse than a lot of traditional TLs anyway. Add ~6db to the response to account for room-gain. That means theoretically around 100db efficiency for 1watt at 30Hz, and still about 90db at 20Hz.

Cabinet internal dimensions are 16.5in wide, and (wait for it) 23.5in deep. Add 2x and 3x width of your chosen build material to these for external width and depth. Cabinet is 75in tall, roughly 150in path length, driver 30.25in down from the internal top (point above the driver).

Hope you Like Jurassic Park guys.

Enjoy
Scott
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Old 9th October 2006, 05:14 PM   #12
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I used the Beta 8 in a mass loaded transmission line, and I tell you- Martin Kings worksheets seem to work quite well. Further, I believe that a really large box could be configured in such a way to get some unusually good bass out of a pro 12" woofer.

However, a problem I ran into was beaming. Even running the 8" driver to a high crossover point, I noticed a big change in sound as I walked around the room. I expect the 12" to be worse.

It might sound great at the sweet spot, but don't expect a big sweet spot. Also, room treatment could become critical in order to get even bass where the 12"s dictate as the sweet spot.
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Old 9th October 2006, 05:35 PM   #13
Variac is offline Variac  United States
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Joe, please keep in mind that the 12" we are discussing has a whizzer cone and is rated as having respnse to 8,000 hz. The small center cone will disperse the higher sound as well as produce it , no?

This particular driver is the key to the idea- it is "full range"- or almost



http://www.partsexpress.com/pe/pshow...90-409&scqty=2


It will still have a cheap, efficient tweeter to get the highest notes.
That tweeter should be rated to go to almost 20k, after all, it only has to cover from 8k up, so a pro driver isn't nevcessary- especially because they don't have the highest top end..
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Old 9th October 2006, 05:41 PM   #14
Variac is offline Variac  United States
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Here are some photos Punkrockr, Remember- yours would be more than twice as wide and a lot deeper- with a 12" driver!!The photos show 6" drivers.They don't need to have the tapered stairstep bottom that one photo shows. The standard model is as shown in that photo that shows the interior- two side panels and edges on three sides with the top open and a single diagonal partition in the middle. If you study the site you will see how this creates a horn inside the box. Easy to make ..

http://www.zillaspeak.com/bib-pics.asp
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Old 9th October 2006, 05:44 PM   #15
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16.5in wide internal just ain't bing enought for some folks...
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Old 9th October 2006, 05:49 PM   #16
Variac is offline Variac  United States
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Check out this tweeter- its pretty flat from 5k to almost 30k. Really good for Punkr's youthful eardrums! and over 98 dB efficient. As I said I have a pair and they sound decent. Lots of people just love them, and pretty cheap at around $35 each. (cheaper from me if punkr actually DOES something!) The important part is that we have TWO designs that use this tweeter with the same 12LTD driver so we can recommend a decent crossover to Punkr.



http://www.madisound.com/pdf/fostexdrivers/ft17h.pdf
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Old 9th October 2006, 05:52 PM   #17
Variac is offline Variac  United States
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Whoops, I missed Scotts' post. Got that Punkr?: 18" wide, two feet deep- no need to turn the cabinet. Also over six feet tall!!!

Those photos are wimpy things compared to this box!

If we can hold the 2' deep dimension, then a sheet of plywood will give you 2 sides.

The other speakers that give us info on the tweeters:
http://melhuish.org/audio/super12.html#forum
http://www.fortunecity.com/rivendell...terburner.html
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Old 9th October 2006, 09:00 PM   #18
tinitus is offline tinitus  Europe
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From what I can read the BIB is a compromise by simulating a number of drivers.... from 5" to 8" .... with a fixed length

Are you really sure this will work with a 12"

I am not good in maths ... but dont you get a big change in exstension of the horn when the slanted inner baffle is that much wider in relation to the BIBs with smaller drivers
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Old 10th October 2006, 06:28 AM   #19
Variac is offline Variac  United States
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heres a pic of the size Scott mentioned, with a 12" driver and a tweeter below.(could be above...) The woman is 5'-6" tall

Since the speaker puts out almost 100db per watt at one meter, lets say you want 10 times that for dynamics and you probably sit more than a meter from the speakers..- That means a 20 watt per channel receiver you can pick up for $25 at Goodwill would blast you out of the house. Especially considerig that you would have TWO speakers!

How come other speakers need hundreds of watts?
Well a lot of people actually find large speakers to be a problem, not a cool thing, and smaller boxes are generally less efficient. Luckily you don't have that problem- maybe Also these are horns, or transmission lines or somethin' with a pretty much full range driver.
Some love 'em some don't. I don't think you are so picky that it would matter.. They will have lots of bass and lots of volume and probably sound pretty cool indeed.
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Old 10th October 2006, 06:46 AM   #20
Pano is offline Pano  United States
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Cool drawing, Mr. V. Not as huge as I had imagined them.
But I think the little girl is scared.

What are we looking at - 4 or 5 sheets of Ply/MDF?


Wonder if I could talk my wife into letting those into the living room - if they were real pretty....
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