So as to not threadjack Bear's A7 thread, here is a thread about horn damping. It's been covered before, but is worth repeating.
I had mentioned good results using Blackston automotive damping tar on the back of the kerfed plywood horns in an Altec A7 cabinet. Others had other suggestions.
Speaking of Bondo for damping Evenharmonics says:
tt398 had this to say:
My question. Does Gravel Guard come in spray cans? They would be easier, or at least cheaper for those of use who don't have a compressor and spray gun.
FWIW, I have 811B horns that rang until they were tightened into a frame. Once the front and back were bolted tight to wood, no more ringing. There is a slight ring still on the front edge, but that should be easy to cure.
Anyone else have good or bad experiences with horn damping they would like to share?
I had mentioned good results using Blackston automotive damping tar on the back of the kerfed plywood horns in an Altec A7 cabinet. Others had other suggestions.
Speaking of Bondo for damping Evenharmonics says:
Evenharmonics said:
tt398 had this to say:
tt398 said:
My question. Does Gravel Guard come in spray cans? They would be easier, or at least cheaper for those of use who don't have a compressor and spray gun.
FWIW, I have 811B horns that rang until they were tightened into a frame. Once the front and back were bolted tight to wood, no more ringing. There is a slight ring still on the front edge, but that should be easy to cure.
Anyone else have good or bad experiences with horn damping they would like to share?
I’ve seen a picture of Altec 511B horn with latex paint mixed with sand and brush applied to dampen it. It would be cheap and quick way to do it but I don’t think it’s as good as Bondo due to limited thickness the paint can hold before start cracking when dries.
If the horn will be covered with enclosure or something (except for its mouth), then the appearance won’t be much of an issue, in which case you can use gravel guard spray / brush on. If it will be highly visible, I would suggest taking it as if it’s your car’s fender – Bondo, sand, prime and paint to match your décor.
If the horn will be covered with enclosure or something (except for its mouth), then the appearance won’t be much of an issue, in which case you can use gravel guard spray / brush on. If it will be highly visible, I would suggest taking it as if it’s your car’s fender – Bondo, sand, prime and paint to match your décor.
most effective way certainly is making box sand for horn,where driver end is enough protruded on back of box , so messing with driver doesn't mean digging horn from dirt 
where this solution from any reason is out of question ,multiple coating with any sort of Gravel Guard is best ........ comming from entire different area I can just guess by name that's coating made for shielding auto chassis bellow doors......brink?
cheap and robust solution is also using felt strips mixed with any tar based coating
edit:
I guess that Gravel Guard can't be in spray doses......it isn't enough viscous for that
where this solution from any reason is out of question ,multiple coating with any sort of Gravel Guard is best ........ comming from entire different area I can just guess by name that's coating made for shielding auto chassis bellow doors......brink?
cheap and robust solution is also using felt strips mixed with any tar based coating
edit:
I guess that Gravel Guard can't be in spray doses......it isn't enough viscous for that
panomaniac said:
I like the schutz gun -- it lets me quickly lay down a thick coat of this stuff -- very handy when doing a large horn like a JBL 2350. Gravel Guard is available in large aerosol spray cans. It stinks like heck when you spray it - a job best done outside. Once dry it has no odor -- and it does a good job dampening the metal horn resonances.
The very very best way to fix a 511 or 811 horn is to crush it in a car compactor.
Of course the sandbox technique is very good, but heavy and hard to move.
The goo on the backside, whatever it is works ok.
The aluminum is already stiff - so it only need to be damped.
Otoh, the Altec Multicells are NOT stiff, and need to be stiff and damped. The old tar + lead that they had gooped on the back of them tends to delaminate off the thin metal. Thus the higher regard for the "tar filled" versions.
Automotive pick-up truck "bed liner" material is worthy of consideration as a DIY paint/spray on for damping.
The problem with the A-7's mid-bass horns is that they are thin plywood, and connected to the LF volume, they need to be stiff to control the bass energy, and to not ring with the midbass energy. So imho, damping is insufficient but necessary for them...
_-_-bear
Of course the sandbox technique is very good, but heavy and hard to move.
The goo on the backside, whatever it is works ok.
The aluminum is already stiff - so it only need to be damped.
Otoh, the Altec Multicells are NOT stiff, and need to be stiff and damped. The old tar + lead that they had gooped on the back of them tends to delaminate off the thin metal. Thus the higher regard for the "tar filled" versions.
Automotive pick-up truck "bed liner" material is worthy of consideration as a DIY paint/spray on for damping.
The problem with the A-7's mid-bass horns is that they are thin plywood, and connected to the LF volume, they need to be stiff to control the bass energy, and to not ring with the midbass energy. So imho, damping is insufficient but necessary for them...
_-_-bear
bear said:
Greets!
It works very well and often used to brush, roll or spray whole PA cabs.
Very true and why if you have 825 cabs the horn sections need to be blocked off and all series filled with kitty litter or similar. Some folks claim the expanding foam will do the trick, but I'm skeptical. If anyone tries it though, be forewarned that if you aren't careful you'll either bulge or completely blow out the thin plywood flares.
GM
As a former boatbuiler, boatbuilder foam has many advantages: strength vs weight, acoustic dampening, great adherence to wood surfaces. Avoiding bowing is a matter of having a rough idea of how much material to mix to fill the cavity, plus a little, and providing vent holes for the excess foam to exhaust through at several locations. Obviously, at the time of the pour, the vent holes must me at the top. Because of the good bonding to wood panels the foam provides strength in tension as well as compression, which can allow elimination of wood cross bracing.
Wow, talk about an old thread coming back...
Concrete is rather transmissive and resonant... stiff though.
There are better materials to use if that is the property that you want, imo.
Concrete can be problematic, although it is easy to get.
Foam in the expanding type sense is problematic, it has not that much resistance to bending by itself, and works best when constrained between two stiff layers. And, generally speaking you don't want it just hanging out with nothing protecting it. Of course there is "hard" foam and "soft" foam - guess ur talking about hard foam, the expandable type...
Imo, in the case of something like the cast aluminum Altec horns, what is needed is energy absorption, the aluminum is plenty stiff already.
In the case of the multi-cell Altec horns, they are made from sheet metal, you need a combination of stiffness and energy absorption. A bit of mass helps too, as it tunes the resonance below the operating point of the horn.
Altec used lead with bituminous compound originally for this very reason. Mass + goo = lower freq resonance and damping.
One needs to select the method and material for the given situation and horn, imo.
_-_-bear
Concrete is rather transmissive and resonant... stiff though.
There are better materials to use if that is the property that you want, imo.
Concrete can be problematic, although it is easy to get.
Foam in the expanding type sense is problematic, it has not that much resistance to bending by itself, and works best when constrained between two stiff layers. And, generally speaking you don't want it just hanging out with nothing protecting it. Of course there is "hard" foam and "soft" foam - guess ur talking about hard foam, the expandable type...
Imo, in the case of something like the cast aluminum Altec horns, what is needed is energy absorption, the aluminum is plenty stiff already.
In the case of the multi-cell Altec horns, they are made from sheet metal, you need a combination of stiffness and energy absorption. A bit of mass helps too, as it tunes the resonance below the operating point of the horn.
Altec used lead with bituminous compound originally for this very reason. Mass + goo = lower freq resonance and damping.
One needs to select the method and material for the given situation and horn, imo.
_-_-bear
I agree. I was reffering to boatbuilder foam which passes USCG for structure. It might be perfect for the multi cell horns, as it is strong. I seems to pretty much lack resonance.
My interest; I just started my first horn project, a sort of A7 inspired BLH with 12" Altec drivers. Came up with foam as a way to help avoid the 3'x3'x4' cabs weighing in as much as a small motorcycle. We'll see what happens. It's still on paper.
My interest; I just started my first horn project, a sort of A7 inspired BLH with 12" Altec drivers. Came up with foam as a way to help avoid the 3'x3'x4' cabs weighing in as much as a small motorcycle. We'll see what happens. It's still on paper.
Epoxy coated foam core as used by boat and surfboard builders is an excellent speaker cabinet material, light, non-resonant and rigid.
It is very expensive and messy to work with, similar sonic results at a fraction of the price can be done with well braced thin plywood.
Art
Have to agree with Bear here...these horns sound like they are ringing even if you completely cover them with raw meat.
I once encased a 511 with a layer of plasticine modeling clay that I found at a Dollar Store. Cost $30 for 30 packs. I also cut the welds in the vanes and installed rubber strips, as I saw done on a very old Altec sectoral with gray paint...led me to think this was the original design intention to damp bell modes.
Dang 511 still had a ringy edge. I concluded that it is in the geometry.
Lots of people are using these sectorals happily, it should be noted.
I always thought the Altec 1" drivers were better than the Altec 1" horns. Right now I'm trying 32B/C to see if I can make that work. so far, so good.
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