Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 448 - diyAudio
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Old 26th April 2009, 12:25 AM   #4471
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Default Re: "Offset" a good idea?

Quote:
Originally posted by Brisso57


Yes. I'd noted that. Frankly, suprabaffles can look a bit weird sometimes. I'd go for the extra-wide front baffle. I've also noted suprabaffles are sometimes used to pack out the driver if rear clearance is tight. In that case, I'd be inserting a whole extra thickness of some cheap material, chipboard maybe.

cheers

Doug

PS If I do make the front baffle wider, is there any benefit in (i) keeping it symmetrical? or (ii) deliberately adding more to one side, to create an "external" offset? (The driver remaining symmetrically set as far as the internals go.)

Well, if you really want to get into this.... A while back some peeps showed a spiral conch shape baffle with a defined ratio for expansion to the edge of the baffle. If you made a left hand and right hand baffle to this ratio and if you stood them together they'd look like a heart as in ..

I heart BIBs.




Maybe someone remembers this and can give the link.

A number of experiments have shown asymetrical wings with the bib design.
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Old 26th April 2009, 01:13 AM   #4472
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Default Re: Re: Date set for the Int'l Build-a-BIB Day!

Quote:
Originally posted by loninappleton

That's what I did with the FE127e: you optimize the height of the driver and GM would say even put it higher to give a good concert effect.
Right, though fill the cavity so it won't 'drum', preferably with something fairly dense such as kitty litter, sterile sand or similar.

GM
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Old 26th April 2009, 01:20 AM   #4473
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Default Re: "Offset" a good idea?

Quote:
Originally posted by Brisso57

.........or (ii) deliberately adding more to one side, to create an "external" offset? (The driver remaining symmetrically set as far as the internals go.)
Ideally, the driver would be offset internally also if the baffle is wide enough, then the external 'wings' would have to overhang both sides to maintain the offset, though the ratios could be different, so there might be an acoustic ratio that only requires a 'wing' on one side.

GM
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Old 28th April 2009, 07:54 PM   #4474
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Default coral 4A-70 project

hi,

reading more, digesting.... with the response from the little 4a-70's being limited below 500hz and a bib filtering backwave energy above 300hz, am i barking up the wrong tree with a bib.

would it be more sensible to jump threads and continue on the open baffle discussion -
saw peter strassackers translucent exponential baffles on lautsprechershop.de....

still waiting for t/s values on corals, will follow that up today,

thanks all, a
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Old 29th April 2009, 04:17 AM   #4475
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Default Internal Offset of Driver

GM, could you expound a little more. After playing with the computer program called The Edge, and experimenting with temporary baffles that are offset, I have concluded that good things happen. The program, and my ears tell me that the FR gets smoothed out, and the missing mid and upper bass get filled in, with my ongoing speaker project.

What will happen if I also move my driver slightly to the left or the right in relation to the vertical center of the cab? I am right at a place where I could do it for my final stage of the longest BIB build in history. I am inclined to position my driver up to a half inch (that is all the room I would have) in the same direction as my "wing".

As far as the wings go, when I played with The Edge, it seemed logical to me to add a second wing on the opposite side, but even a tiny amount would make the FR bumpy again.

Sincerely,

Benjamin
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Old 29th April 2009, 03:05 PM   #4476
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Default Re: coral 4A-70 project

Quote:
Originally posted by arustyrednail

reading more, digesting....
Greets!

Obviously, small drivers can only sound truly 'big' if compression loaded with a large horn to increase its radiating area, which severely BW limits them, but pipe horns (especially if corner loaded) can provide enough acoustic gain to ~tonally balance a small/low Xmax driver to well below its Fs and where it begins filtering backwave energy is a function of its effective Qts and surrounding boundary loading (baffle, etc.), so we won't know anything definite until the specs are in.

If you want to get the best out of a 'FR' driver though, then OB with both a woofer and super tweeter system is required, which of course drastically increases design complexity with its own set of performance trade-offs.

Your call..........

GM
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Old 29th April 2009, 03:17 PM   #4477
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Default Re: Internal Offset of Driver

Quote:
Originally posted by BenjaminWebber
GM, could you expound a little more.
'Expound' in what way? I haven't used the 'Edge', much less compared it with real world measurements, but considering who designed it I imagine it's theoretically correct, which is about all one can reasonably expect from a sim, so it can be used to to see how moving the driver across the BIB baffle affects it internally or externally, though I assume it won't do both at the same time, ergo a certain amount of interpretation on your part is required to 'see' the summed effect.

That said, unless a cab is wide enough for its wall's eigenmodes to be down in its BW, then offsetting a driver is a waste of time since the internal wall damping will quell them, so concentrating on getting the external baffle size/shape and driver offset right is all that matters.

GM
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Old 29th April 2009, 07:05 PM   #4478
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Default coral 4A-70 project

to the woodshop!

picked up my corals from axent - still no t/s figures.... making a tiny enclosure to test 'em is , it seems, in the too hard basket for them....

however, i cornered kelly the bossman there - he's sure they have the specs for the corals from '83 when they used them last....

confirmed that the 4a70 will work in a back loaded horn, a super slim tl or bottom ported mltl.... can rummage up appropriate filter components to blend to a woofer if needed......

suggested tuning to about 90hz and working down, so it seems best thing for me to do is the classic bib form for mk 1 and just see how it sounds.

thanks gm, confirmed my very rough understanding of tiny-driver/bib principle....

will see if i can get panels cut this weekend,

a
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Old 30th April 2009, 12:12 AM   #4479
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Default coral 4A-70 project

hello again,

checked in with friendly woodworker, going ahead with mk 1 dimensions, maybe ready by sunday ( hope someone touching wood )

for mk 2 - any advantage to 'stretching' the recommended line to a full ten feet, (5ft folded...) keeping volume equivalent... making taper longer ratio, narrower baffle, longer delay to backwave?

(room actually tall enough to take 10 ft unfolded - a couple of feet to spare, art nouveau apt, originally had gas light fittings; front room roughly 12w x 19l x 14h, going by my 6ft reach and a bit of squinting...)


thanks, a
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Old 30th April 2009, 06:33 PM   #4480
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Greets!

Increasing its path-length lowers Fp and its 3rd harmonic dip, so it may, may not be beneficial and the lower it's tuned below Fs the more critical the need for room loading to protect the driver from over excursing, so based on your room's dims, I'm thinking there might not be enough corner loading to do it, but only one way to know for sure...........

GM
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