Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks? - Page 514 - diyAudio
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Old 26th January 2013, 02:12 AM   #5131
xrk971 is offline xrk971  United States
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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.
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Old 26th January 2013, 11:20 AM   #5132
Squeak is offline Squeak  Denmark
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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.
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Old 26th January 2013, 12:22 PM   #5133
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Default 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.
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Old 26th January 2013, 01:16 PM   #5134
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Originally Posted by xrk971 View Post
I thought about the inverted V divider (if that is what you mean by a V shaped divider - good point about bracing), would that not split the mouth into two horns and thereby change the lowest freq the horn can reach due to reduction of the mouth circumference. The curved single divider wall is merely to provide additional clearance for the driver. One option is to make the V divider lower than the top of the box so that the two horns can merge back into one and maybe provide the larger horn mouth?
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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Last edited by zayne742; 26th January 2013 at 01:21 PM.
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Old 26th January 2013, 02:00 PM   #5135
xrk971 is offline xrk971  United States
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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.
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Old 26th January 2013, 04:17 PM   #5136
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It looks like you're making a desktop model of a Cerwin Vega Earthquake sub.

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Old 26th January 2013, 07:07 PM   #5137
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At present I have an Cambridge integrated amp and a Sonic T-amp (that I plan to modify) but think that something along the lines of a bottlehead S.E.X. lamp is on the way. Basically, I'll build the speakers and then tailor the amp to them.

So if I interpret what you are saying correctly, the presswood or particleboard is a bad idea for the rear panel and should build it with 1 inch ply to increase the stiffness of the cabinet. If need be, I can adjust damping with felt or stuffing. What about the slant? Optimally, do I want particle board or plywood?

-andre-
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
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Old 26th January 2013, 10:12 PM   #5138
xrk971 is offline xrk971  United States
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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.
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Last edited by xrk971; 26th January 2013 at 10:28 PM.
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Old 26th January 2013, 10:48 PM   #5139
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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.

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Old 26th January 2013, 11:03 PM   #5140
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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.
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