I'm just catching up on the last week or so, and I see that GM has put forth an easy way to design a BIB. Just so I've got my head around it, here's what I've gotten from it, correct me if I'm wrong:
(variable names refer to those in this diagram, I've also added some annotations.)
Inputs:
Outputs:
Tom.
(variable names refer to those in this diagram, I've also added some annotations.)
Inputs:
- Fs (tuning frequency of BIB)
- Vas
- Qts
Outputs:
- formula: L = (13464.54(SpeedOfSound in inches/second))/2(half wave) /Fs (tuning Freq)
- formula: H = L/2 (folded)
- formula: Vb = 20*Vas*(Qts^1.25)
- formula: Sm = Vb(in ft^3)*(12^3 (inches in ft^3))/L (should be H?)
- formula: D = (Sm * (2^.5))^.5(pseudo golden ratio?)
- formula: W = Sm/D
- formula: Zd(So?) = L * 0.217 (fudge factor?)
- formula: a,b,c = D/2
Tom.
renfrow said:
Greets!
Yes, should be 'H'.
Not really, though it's a very good acoustic ratio also, but it was chosen due to it ~preserving the expansion through the bend.
No, it's the driver off-set from the closed end chosen for a good balance between flattest response and max gain BW.
GM
Re: Re: Bib tweak update attn: GM
I can't breathe through foam padding either. That's what's in there now but not cut to the right size. 'Don't know what some gauzy stuff in there would do.
As to shape, depending on the orientation, the bottom part can be
pretty much parallel to the top or if hung crosswise would be tapered.
The goal is to control boominess. I'm trying to get my ears working to identify what it is I should be hearing out of the top.
In normal listening position, the foam thingy has provided some benefit. The only interior treatments are a square of stuffing at the base and a bit up in the closed end peak.
Perhaps use the felt along the divider (as others have done) or hung loose at the rear?
GM said:
I can't breathe through foam padding either. That's what's in there now but not cut to the right size. 'Don't know what some gauzy stuff in there would do.
As to shape, depending on the orientation, the bottom part can be
pretty much parallel to the top or if hung crosswise would be tapered.
The goal is to control boominess. I'm trying to get my ears working to identify what it is I should be hearing out of the top.
In normal listening position, the foam thingy has provided some benefit. The only interior treatments are a square of stuffing at the base and a bit up in the closed end peak.
Perhaps use the felt along the divider (as others have done) or hung loose at the rear?
Greets!
If I can't breathe through it (or blow very low pressure air through it if fiberglass or similar), then I don't use it in a cab for reducing reflective energy. To control 'boom', the traditional method was to stretch a membrane across the vent or mouth and one reason why speakers, BLH horns were 'voiced' with very taut, close fitting grill cloths, sometimes even multi-layered.
GM
If I can't breathe through it (or blow very low pressure air through it if fiberglass or similar), then I don't use it in a cab for reducing reflective energy. To control 'boom', the traditional method was to stretch a membrane across the vent or mouth and one reason why speakers, BLH horns were 'voiced' with very taut, close fitting grill cloths, sometimes even multi-layered.
GM
Im sure its somewhere in these 299 pages, but how do I get from the line length and mouth areas given on Godzilla's site to actual interior dimensions? Height and interior divider length in particular.
L = (Line length) 136in
Zdriver = Driver 27.5" down from sealed end of cabinet
Sm = 87.75in^2
Will likely be using 3/4" wood. Driver is Fostex FE166 ES-R.
L = (Line length) 136in
Zdriver = Driver 27.5" down from sealed end of cabinet
Sm = 87.75in^2
Will likely be using 3/4" wood. Driver is Fostex FE166 ES-R.
Quite easy, if you think about it for a sec...
The sound travels HORIZONTALLY at the bottom....
If you take the center of the line, the horizontal distance is HALF of the 'depth'...
See the red line here: http://www.zillaspeak.com/bib-howtobuild.asp
Cheers, Paul
The sound travels HORIZONTALLY at the bottom....
If you take the center of the line, the horizontal distance is HALF of the 'depth'...
See the red line here: http://www.zillaspeak.com/bib-howtobuild.asp
Cheers, Paul
ChrisMmm said:
Greets!
I've repeatedly posted that if you use a SQRT(2) 'Sm' width:depth ratio, then dividing L/2 preserves 'close enough' the area expansion through the bend AFAIK, so no need to add any depth to it as Dave's calculator does or any internal baffle thickness as others keep saying. AFAIK no one has shown me where I'm wrong, so that's my 'story' and I'm sticking to it.
Once you move away from this ratio though, for best accuracy you have to figure out how the expansion changes and any impact it has on the acoustic path-length (L). Regardless, IIRC Scott used MJK's more advanced WS that plots the expansion through bends to sim the original BIB, mine, and some other combos and they were all acoustically close enough that I doubt the differences would be audible in-room unless the ratio deviates too far from the ~ideal.
As always though, YMMV.
GM
resident said:
Do I need to leave the base removable?
For damping or whatever?
Some use felt, some not, what to do?!
Greets!
If you don't have a way to install/remove damping material till you find what sounds best to you, then a removable side or bottom seems mandatory in the case of a pipe horn. I never used felt in them other than on the driver or any stuffing in the bend IIRC, instead dealing with any excessive reflections/'boom' with damping at the throat and/or at the mouth. Parallel wall reflections were dealt with by selective damping around the driver and by various means/materials as required, so the bottom line is that it's too subjective for anyone to arbitrarily spec what material(s)/quantity is to be used where inside BIBs for all systems.
GM