Exactly, the two mouths become one and the waves combine.
Some old horns with this construction also make the divider slightly asymmetric to combat ribbling and avoid too much stuffing to do the job.
It won't completely solve the problem of space because the basic geometric problem is the same no matter how much you slice the space. But it will allow for more flexibility on the placement and shape of the divider since now it doesn't rely on the frame.
Some old horns with this construction also make the divider slightly asymmetric to combat ribbling and avoid too much stuffing to do the job.
It won't completely solve the problem of space because the basic geometric problem is the same no matter how much you slice the space. But it will allow for more flexibility on the placement and shape of the divider since now it doesn't rely on the frame.
OK, so I am torn. Should I build the FIB as I have drawn it above or with the inverted "V" in the middle like below? I think if I stick with the one as drawn (single diagonal) it will have more of a chance of sounding like what I expect a BIB to sound like. Going with two horn mouths could result in something totally different.
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Squeak,
That is a mouthful... MLTQWT... mass loaded tapered quarter wave tube? How is it mass loaded - there is no constriction on the mouth? I think the slight exponential mouth will enhance the performance if anything. Not sure why this is limited to low Qts drivers - as long as you use the BIB calculator, which, IIRC relies on the magic alignment formula that GM came up with: BIB volume is proportional to Vas*Qts^1.2.
Well maybe the ML part was overdoing it. 
The point was that it starts of with expanding less and less. Essentially something like a transmission line with only a little hornloading, which is good for high Qts drivers but not for something like FE126. Then it goes into an almost straight section with a turn and expands into a horn.
Have you considered not folding it? If you have reasonably tall ceilings you will get the mouth closer to them. You will also get a different, perhaps more elegant visual impression that way.
If you make them a long wedge, and you put the driver on the flat side you'll have the driver pointing slightly down, which is perhaps not a bad thing if you put them a bit above ear level.
If you put them on the other pointed side you'll run into the same problem of space that you solved by curving the divider. You could also solve it, again i guess more elegantly, by squashing/flattening the wedge more than 4 inches to make it wider.
Then you'd of course have to make sure that the magnet doesn't create a choke point. Perhaps by making the whole, or part of the front baffle thicker.
The point was that it starts of with expanding less and less. Essentially something like a transmission line with only a little hornloading, which is good for high Qts drivers but not for something like FE126. Then it goes into an almost straight section with a turn and expands into a horn.Have you considered not folding it? If you have reasonably tall ceilings you will get the mouth closer to them. You will also get a different, perhaps more elegant visual impression that way.
If you make them a long wedge, and you put the driver on the flat side you'll have the driver pointing slightly down, which is perhaps not a bad thing if you put them a bit above ear level.
If you put them on the other pointed side you'll run into the same problem of space that you solved by curving the divider. You could also solve it, again i guess more elegantly, by squashing/flattening the wedge more than 4 inches to make it wider.
Then you'd of course have to make sure that the magnet doesn't create a choke point. Perhaps by making the whole, or part of the front baffle thicker.
Squeek,
Interesting thoughts about unfolded BIB - kind of like upside down Voigt pipe without mass loading. could be interesting visually and I like idea of pointing driver down. However, it becomes too imposing and WAF goes down. The V in the middle, if it splits the mouth, the circumference of the horn is cut in half and this is what affects the ultimate low freq. That is why I wanted the horns to combine and form same circumference again.
Interesting thoughts about unfolded BIB - kind of like upside down Voigt pipe without mass loading. could be interesting visually and I like idea of pointing driver down. However, it becomes too imposing and WAF goes down. The V in the middle, if it splits the mouth, the circumference of the horn is cut in half and this is what affects the ultimate low freq. That is why I wanted the horns to combine and form same circumference again.
There will be virtually no difference whether the two wavefronts combine shortly before exiting the cab or just outside it.
About WAF: If the wife has the last word, I'm not so sure she wouldn't be more inclined towards longer more slender cabs, rather than having two of the monolith from 2001 a Space Odyssey on the wall? And If the former gives better bass and is easier to build (no extra braces and bending), then why not?
About WAF: If the wife has the last word, I'm not so sure she wouldn't be more inclined towards longer more slender cabs, rather than having two of the monolith from 2001 a Space Odyssey on the wall? And If the former gives better bass and is easier to build (no extra braces and bending), then why not?
The long ones require joining two sheets of foam core as max length is 30 in. If I made it in plywood or masonite then no problem. Not sure if the single long one would sound better. The fold allows one to put stuffing at the turn to absorb some of the higher frequencies and the corners act as naturnal low pass filters.
The long one would be just as easy to stuff if you put an X of string in the pipe to keep the stuffing from sliding down.
True, the corners will to some small degree work as filters, but you will also gain some efficiency with the straight pipe. You'll be able to better fine tune and balance between efficiency and HF output with stuffing alone.
You'll need exactly the same amount of baffle material for both approaches. Just cut the sheet into two strips and make sure the seam is airtight.
Clad the whole thing in wallpaper for a fast and wife friendly finish.
True, the corners will to some small degree work as filters, but you will also gain some efficiency with the straight pipe. You'll be able to better fine tune and balance between efficiency and HF output with stuffing alone.
You'll need exactly the same amount of baffle material for both approaches. Just cut the sheet into two strips and make sure the seam is airtight.
Clad the whole thing in wallpaper for a fast and wife friendly finish.
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I have been thinking about the flatness of the FIB and think I may want to go with 3 in deep as 4 in is still kind of thick for a wall hanging. That will make it 16 in wide now. I am still leaning towards the folded approach as that makes transport and more flexible to mount in smaller rooms without tall ceilings.
Squeak, you ought to make the straight FIB and I will make the folded one. I think if is straight it is no longer a BIB design but a generic conical tapped horn.
Squeak, you ought to make the straight FIB and I will make the folded one. I think if is straight it is no longer a BIB design but a generic conical tapped horn.
Semantics... Personally i don't bother with that in cases like this. ;-)
FiB, BiB, tapped horn etc. It's all more or less the same thing going on.
Good choice with the folded version if the portability and generality is your criteria. And I don't think you'll regret making it less deep and wider. Just make sure there is room on the wall where you plan to put them.
FiB, BiB, tapped horn etc. It's all more or less the same thing going on.
Good choice with the folded version if the portability and generality is your criteria. And I don't think you'll regret making it less deep and wider. Just make sure there is room on the wall where you plan to put them.
Update on FIB build in foam core
I decided to go with the 16 in wide x 27 in tall x 3 in deep FIB with an offset inverted V center channel. I am just about to glue the face on with PVA. The size feels good when I hold it up to a wall - like an average sized poster or painting.
I decided to go with the 16 in wide x 27 in tall x 3 in deep FIB with an offset inverted V center channel. I am just about to glue the face on with PVA. The size feels good when I hold it up to a wall - like an average sized poster or painting.
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Looks good! How high will the driver placement be on the wall?
You could possibly put a bend, think very open V, in the end cap for strength. This could keep it from rattling. You could go from each end to the center brace you added. It could be one solid piece, with a crimp in the middle.
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Zayne,
The driver will be ear/eye level so works well as a painting if I decorate it. I was going to add a shallow V on the bottom cap to reduce direct reflections back up. I will make it removable to adjust stuffing easily. The PVA glue is drying right now clamped with books and dumbells. I hope it works.
The driver will be ear/eye level so works well as a painting if I decorate it. I was going to add a shallow V on the bottom cap to reduce direct reflections back up. I will make it removable to adjust stuffing easily. The PVA glue is drying right now clamped with books and dumbells. I hope it works.
Greets!
You’re welcome!
Hmm, best overall to tailor the speaker to the amp, i.e. build them too large acoustically, so that it won’t cause the flea power amp to ‘lay down’ trying to drive a smaller than optimum net Vb due to the amp’s high output impedance effectively weakening the driver’s motor [raising Qes/Qts].
lacking any SEX amp specs, I can only assume it’s a ~matching impedance, so using a ~0.4 Qts to calculate the BIB should be plenty high enough and if it should sound too ‘boomy’/’loose’ and/or has too much mid-range coming out the terminus with the higher DF amps, then you can either add some series resistance and/or more stuffing initially.
No, I explained why it’s not the best choice for any of the BIB’s panels, but will be fine if braced well, especially if it will be hard up against a wall or corner, i.e. not ‘gapped’ by a baseboard, chair rail, wainscoting or similar; and since scrap material is cheap, bracing would be my choice if keeping overall cost down is required.
I wish I had pictures of some of my old builds, there were some that looked more like a ‘Birdcage’ Maserati’s frame than simple speaker cab since I would use up as much scrap as I could when I knew it would be getting some type of veneer to cover up any visual mismatches.
GM
GM,
I just put the FIB together with the driver and it just does not sound like a BIB at all. I am afraid the split path with inverted V is completely different in character as the huge BIB mouth circumference is now replaced by two much smaller mouths. I had to really pull the stuffing to very little in closed end above driver and a little beneath. It could be that I have not sealed the bottom cap on with glue as I needed to adjust the stuffing. A tiny leak can cause problems in a horn- that might be the reason... Right now the bottom cap has a lip to help provide a static seal but probably still not airtight. Sealing it with glue will committ me to the stuffing in the lower section, although you can still pick at it thru driver cutout, just more difficult. Maybe all I can do is seal with glue and see.
I just put the FIB together with the driver and it just does not sound like a BIB at all. I am afraid the split path with inverted V is completely different in character as the huge BIB mouth circumference is now replaced by two much smaller mouths. I had to really pull the stuffing to very little in closed end above driver and a little beneath. It could be that I have not sealed the bottom cap on with glue as I needed to adjust the stuffing. A tiny leak can cause problems in a horn- that might be the reason... Right now the bottom cap has a lip to help provide a static seal but probably still not airtight. Sealing it with glue will committ me to the stuffing in the lower section, although you can still pick at it thru driver cutout, just more difficult. Maybe all I can do is seal with glue and see.
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Yeah, in the right place, a near pin prick is sufficient to let most of the horn's pressure bleed off. I've seen many drivers not perform well because their surround was a little porous.
You can temp seal it with neoprene gasket or even BluTak.
Two smaller mouths shouldn't make a difference if they sum to same CSA except higher up due to the shorter eigenmodes across them, so at worst you may need to damp their perimeters.
GM
You can temp seal it with neoprene gasket or even BluTak.
Two smaller mouths shouldn't make a difference if they sum to same CSA except higher up due to the shorter eigenmodes across them, so at worst you may need to damp their perimeters.
GM
As already said there is very little physical difference between the one-mouthed and two mouthed approach. If anything it probably has more to do with the radical shape of the cab. But I can't think of what the exact problem could be.
Have you boundery loaded it?
Idealy a BiB should be pushed in a corner or at least have some half-space boundary loading, like ceiling and wall.
Try inverting them.
Your spiral horn worked fine and since this looks to be the same driver, you shouldn't get that much of a difference in result. At least more bass quantitatively, because of the larger size of the cab.
Have you boundery loaded it?
Idealy a BiB should be pushed in a corner or at least have some half-space boundary loading, like ceiling and wall.
Try inverting them.
Your spiral horn worked fine and since this looks to be the same driver, you shouldn't get that much of a difference in result. At least more bass quantitatively, because of the larger size of the cab.