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Old 19th February 2013, 08:48 PM   #1331
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One quick question; how the heck do you get the drivers mounted in the foam core? It is hard to imagine the screws holding well enough in that stuff.

Or, perhaps it is because you have all been typically using quite small drivers, with light magnets.

I would hesitate to put a pair of Alpair 10.2 in foam core without some re-enforcement.
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Old 19th February 2013, 08:51 PM   #1332
xrk971 is offline xrk971  United States
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Cogitech,
An option is to either butt-join the smaller 20x30 sheets from the dollar store with a simple hot-melt strip of 2 in wide foam core on one side and stiff paper and PVA on the other side. Build it as large as you need - the problem may be how thin it is. Can double up foam core sheets to 3/16 in thick as IG has done. Alternatively, 4x8 sheets in 0.5 in and 0.75 in thick isocyanuratae foam sheathing at HD or Lowes can serve nicely as the main side panels on a large double horn like the Silbury. These foam sheets are only $12 ea, although I don't think they have a paper facing so something like acrylic adhesive or caulking might be used as the glue. Hot melt works too but you have such long runs it can get expensive in glue. Or use hot melt to tack, and caulk to adhere and seal.

R-Matte Plus 3 R-3.2 1/2 in. 4 ft. x 8 ft. Foam Insulating Sheathing-754404 at The Home Depot
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Old 19th February 2013, 09:37 PM   #1333
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Yes, I considered the option of joining or overlapping the 20x30 sheets. Maybe will still try that.

I am actually also looking at OSB as a build material (although this goes way off topic, sorry).
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Old 19th February 2013, 09:45 PM   #1334
xrk971 is offline xrk971  United States
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Cogitech,
To mount the drivers in foam core, you need to reinforce the cutout area. Typically, for smaller drivers I glue small pieces of wood to the back where the screws go and drill through that so the screws have something to grab. For an Alpair 10, it weighs quite a bit, so double up on the foam for the baffle and reinforce with thin hobby plywood if needed - cut with a knife or small hand jigsaw - as long as you don't use a real power tool (gasp, shudder, heaven forbid the thought ). If you go with the half inch sheathing foam insulation, it is probably quite strong but needs wood to reinforce where the screws go. Dr Boar had great success with OSB on the MJK Horn thread in case you haven't see that. What are you thinking of building first? If you are new to this, believe it or not, the Cornu spiral is a great beginner project - it is easy to make, doesn't take much foam, and the rewarding beautiful sound can't be imagined considering what it all started as. If you want to try a more traditional looking box speaker, certainly a MLTL is very doable and they sound great in foam. A little more challenging but awesome sounding and looking is the FH3-inspired horn - one of my favorites. I also love the look and sound of the Flat BIB (FIB). Or you can make a regular BIB like s Mag did - they sound really good and are easy to make. You can also take one of your $10 W3-881si and build another nanotower, this time do some sims to make it an optimized MLTL. The 881si works great in a Cornu too.
Good luck!

Last edited by xrk971; 19th February 2013 at 09:51 PM.
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Old 19th February 2013, 10:01 PM   #1335
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Quote:
Originally Posted by xrk971 View Post
Cogitech,
To mount the drivers in foam core, you need to reinforce the cutout area. Typically, for smaller drivers I glue small pieces of wood to the back where the screws go and drill through that so the screws have something to grab. For an Alpair 10, it weighs quite a bit, so double up on the foam for the baffle and reinforce with thin hobby plywood if needed - cut with a knife or small hand jigsaw - as long as you don't use a real power tool (gasp, shudder, heaven forbid the thought ). If you go with the half inch sheathing foam insulation, it is probably quite strong but needs wood to reinforce where the screws go.
Thanks for the pointers. I have all kinds of tools, both manual and power, so I'll figure something out.

Quote:
Dr Boar had great success with OSB on the MJK Horn thread in case you haven't see that.
I didn't see that, actually, but everything I know about OSB makes me think it would be a fantastic (much cheaper) alternative to BB as long as attention is paid to bracing. Throw some veneer on and who would know the difference?

Quote:
What are you thinking of building first? If you are new to this, believe it or not, the Cornu spiral is a great beginner project - it is easy to make, doesn't take much foam, and the rewarding beautiful sound can't be imagined considering what it all started as. If you want to try a more traditional looking box speaker, certainly a MLTL is very doable and they sound great in foam. A little more challenging but awesome sounding and looking is the FH3-inspired horn - one of my favorites. I also love the look and sound of the Flat BIB (FIB). Or you can make a regular BIB like s Mag did - they sound really good and are easy to make. You can also take one of your $10 W3-881si and build another nanotower, this time do some sims to make it an optimized MLTL. The 881si works great in a Cornu too.
Good luck!
I really want to get a pair of A10.2 going. My friend and I each have a pair and he wants me to build his first, but neither of us can decide what cabinets we want. He seems to have chickened out on the Silburys and I think he has almost decided that Jim Griffin's MLTL is the one for him. I am very, very interested in the Silburys, but haven't made the commitment ($$ - plans) yet.

I was considering building FH3 to see if I like "horns" or not, but I don't think a FH3 will tell me anything about Silbury.

Perhaps I will start by building my buddy's A10.2s into foam core Jim Griffin MLTL and go from there. I'd like to at least start burning in a pair of them, as I have had them for weeks and feel guilty every time I see the boxes.

I think Cornu looks cool, but A10.2 in Cornu would have to be what... 8 feet by 8 feet?

Oh, and the W3-881SI are staying exactly where they are. That, my friend is synergy defined.

Last edited by cogitech; 19th February 2013 at 10:04 PM.
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Old 19th February 2013, 10:10 PM   #1336
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If you want foam front and back you can always add wood Suprabaffles as I did with cutoffs from the 48" square panels from the first build or any scrap for that matter. Pics are at home, I will be there soon and can post or you can look in the Cornu thread.
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Old 20th February 2013, 12:18 AM   #1337
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Cogitech,
Here is the OSB horn thread. MJK's Fostex FF125wk BLH project
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Old 20th February 2013, 12:31 AM   #1338
guangui is offline guangui  Puerto Rico
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My first Foam Core project! Not the prettiest, but will get there....Picture order, after and before paint.

uFonken FC Painted.JPG

UFonken FC Pair.JPG
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Old 20th February 2013, 12:36 AM   #1339
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The after is nice looking - what kind of finish is that? How do they sound?
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Old 20th February 2013, 12:44 AM   #1340
KLBIrd is offline KLBIrd  United States
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In the famous Stromberg-Carlson Acoustic labyrinth or, transmission line, of the 1930s, the tunnel was made of heavy cardboard with felt damping. The radios sold from $300 to $900 and were the high end audio of the day. So we learn that they did it first, and if foam had been available, they would have no doubt used it also.
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