Why aren't we building horns this way?

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#21
#22
I will say that there is more to the OS profile than meets the eye, and I suspect that it would work better than a simple radius at the entrance of a conical horn at hf. I'd guess (I'm not a math guy so I can't say for sure) Doc G shows mathematically how the OS profile is the lowest diffraction cd contour there is in his book. That said maybe a well-thought radius on a conical horn that matches the cd exit would be fairly close.
 
#24
natehansen66 said:
I will say that there is more to the OS profile than meets the eye, and I suspect that it would work better than a simple radius at the entrance of a conical horn at hf. I'd guess (I'm not a math guy so I can't say for sure) Doc G shows mathematically how the OS profile is the lowest diffraction cd contour there is in his book. That said maybe a well-thought radius on a conical horn that matches the cd exit would be fairly close.
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Maybe we 3D print the throat radius section to mathematical perfection for an OS and mate it to a conical at some distance downstream to save on print costs.
 
#25
natehansen66 said:
I will say that there is more to the OS profile than meets the eye, and I suspect that it would work better than a simple radius at the entrance of a conical horn at hf. I'd guess (I'm not a math guy so I can't say for sure) Doc G shows mathematically how the OS profile is the lowest diffraction cd contour there is in his book. That said maybe a well-thought radius on a conical horn that matches the cd exit would be fairly close.
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Willing to bet a jewel that whatever radius that causes the smoothest transition is going to be right in there with the OS profile. Wanna know what really causes horns to sound "unhorny"? Getting away from parallel walls as quick as you can but without diffraction. Unfortunatly this also minimises the good part of horns and that is loading the driver which minimises diaphragm or cone movement. Less movement better distortion figures. Looks to me like a conical horn as large as is needed for the cutoff as deep you can tolerate for given dispersion with a smooth radius driver transition at the throat and a rounded over lip at the mouth is what we have been going for (sans geometry and math smoke) (-:
 
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#27
When our wives stand between two mirrors that reflect here back and forth to infinity, we arw looking at an optical version of "homs" I would think. Parallel mirrors, parallel horn walls. So turn a mirror out or you will get "higher order wife modes"
 
#32
Pano said:
How much would it cost to coat a foam horn? I was looking at prices of truck bed liner and it ain't cheap.
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A friend of mine uses bedliner spray kits from eBay with good success. Some of the kits even come with a spray gun, which is great because this stuff is thick and will clog easily.


He's a pro sound guy, and uses it on his builds. We used it on my 'w' bins recently as well:

IMG_1677_zpsz90vvuc8.jpg




and:

IMG_1721_zpscxx2bxju.jpg




We sprayed the w bins, and 2 of those 4 tapped horns from a 'raw' state, the 2 other tapped horns just got a touch up coat. The W bins and the 2 tapped horns got 2-3 coats each. The whole spraying session was done with an 8L kit from this seller:

Bed Liner Custom Coat Black 4 L Urethane Spray on Truck Kit w Free Spray Gun | eBay


If you're going to spray that stuff, do it outside and get a ton of plastic to put down, or you'll bedliner your driveway 😀

It is definitely tough stuff, and seems to hold up to punishment very well. It's probably even available less expensively than the ebay kit route, I've not looked. You can get tintable colors too, which could be fun.
 
#36
adason said:
Just make sure that solvent in the spray does not disolve the foam before you spray it.
I build recently open baffle with foam from home depot, the pink one 2x2 ft, 1" thick, and truck bed liner is partially disolving it.
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I wonder if the foam needs to be primered first?

I think rc/fpv folks use some kind of spray paint to prime their foam wings/etc.
 
#38
X, it's worth mentioning that your much-vaunted hot glue can also melt certain types of foam [emoji41]

While I have not yet tried this, somebody should try using shellac as a sealer between melt prone foams or other plastic and volatile solvent. *This unusual woodworking product, made from a combination of the world's most popular recreational drug and ground-up insect parts from East Asia, is traditionally used for sealing in smoke or cat urine odors before painting a wall.

* this I have done, but unless you were soaking a mannequin head in xylene and paint solution, that is not likely to happen with speaker building. [emoji41]
Sent from my SPH-L300 using Tapatalk
 
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#39
I've done a fair bit of building with foam. Random observations:

1) foamular is great, but hard to find. I can't get it in CA.

2) the foam glue they sell at home depot doesn't work. It delaminates with ease

3) gorilla glue works. T-88 epoxy works even better.
 
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