For an "Old Guy" he has pretty sharp eyes!
For an "Old Guy" he has pretty sharp eyes!
Did some work yesterday on bracing and damping the bass horn flares.
Though my cabs are made of nice 3/4" ply (the type with the smooth paper on one side that is used for signs) the horn flares are thin, thin. Some of the 825 box plans I have call for semicircular braces behind the flares, mine have no braces. And they resonate like crazy. So I have undertaken to fix that.
First I made a cardboard template for the brace. The radius of the flare is 31". Once I was sure that the template fit, I cut 4 braces out of 3/4" OSB (scraps I had). Plenty beefy. Since I did not want to screw through the flare to hold the brace, I had to come up with a support and clamping method.
Along the straight outside wall I ran a little wooden strip to support the brace. On the back of the flare I put 2 wooden support blocks. For all this gluing I used Gorilla Glue as it is strong and expands to fill gaps. I knew there would be gaps. On the first part I used tape to hold the supports while the glue cured. Not great. The expanding glue kept lifting the blocks. On all the others I used 2 dabs of hot glue along with the Gorilla to "clamp" the block in place. Worked great!
Once the support blocks were in place, I put in the semicircular braces. More Gorilla glue.
The difference is already huge. The stock, unbraced flares were very resonant. They sounded exactly like what they were. Thin, unbraced plywood under tension. Tapping on them produced a low "tunk-tunk" sound. With the braces, it's now "tap-tap" and much lower in amplitude. Big step forward.
Next - damping.
Damping.
Now that the bracing is done, I have moved on to damping the back of the bass horn flares. As they are very thin and right in the signal path, they need to be deadened.
On the pair I worked on in Paris, we used a non-harding tar for the damping. It came in a can and I spread in on with a putty knife. A nasty, smelly, messy job, but it worked a treat! Remember that Altec made tar filled horns.
I've been looking for something that would damp as well, but not be so nasty.
Looked at plaster, concrete, wood putty, foam, caulking, paper mach?, peanut butter, buffalo dung, etc. All have their merits, but also drawbacks. I needed something that would stick, but also remain flexible. It needs to damp the energy that hits the flare.
What I have ended up with is Asphalt Emulsion. This is used to patch roofs. It costs about $11 a gallon and it's water clean up. Nice! No fumes, no volatilities, no worries.
I really does not have much smell. And it's like a very thick latex paint - goes on with a brush. Black as pitch, too.It looks like a gallon will be far more than enough.
I have put one base coat on one speaker so far. Today I will try more coats. My plan is to mix sand into the emulsion to thicken and damp it even more. In stock form the emulsion is not thick enough to do much good, so it will take several coats. Loading it with sand should help a lot. The "Tar in a Jar" I used so many years ago at least had the advantage of going on super thick. Fast work, if a bit smelly and nasty.
Wish me luck with the sand!
Looks like you found a damping solution.
I've had success in using another roofing product-- Modified SBS self-adhesive roofing base (small, 12" wide rolls of this can be found at home improvement stores). One can also build up layers and then use a staple gun to ensure good fastening.
Good luck with your project!
Darn! Wish I had seen that stuff!Originally Posted by sba2
I've used the self adhesive damping mats they sell at Parts Express. Works, very, very well. $$$, tho....
A pair of monitors i recently acquired are damped with a compound that appears to be some sort of rubber compound that contains a fair amount of very fine sand or similar aggregate. It's applied to everything including the drivers themselves, 1/2 inch or thicker on the larger panels. Appears to have been applied with trowel and putty/taping knife. I'd love to find out what it is, and where to get it. It's a pale light gray/green in color.My plan is to mix sand into the emulsion to thicken and damp it even more.
Was it this forum and maybe Old Guy or GM that mentioned stuff they use to sound deaden AC and heating ducts?
Not all vegetables make good leaders.
Sounds like too much $$$/work. Blocking off the cavities and filling them with oil dry/kitty litter worked extremely well for me and some folks have used sterilized sand or Portland cement, but this seems extreme overkill to me. A number of folks have been pleased using expanding foam, but I'm not convinced it mass loads the flares enough to push their Fs to below the horn's ~150 Hz lower corner frequency, so without measured comparisons it's just an opinion.
Then there's the top and bottom to consider. A massive horn sled solidly mounted to the top is desirable as is mass loading the bottom panel with scrap wood or similar. You lose some net volume (Vb), but it's not needed except for when being driven by the most extreme output impedance systems that no one around here seems to use anymore.
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Yeah, I've never tried it, but I'm told it works well. I use to have a link to it, but can't find it ATM.
I've mentioned duct seal to damp driver baskets, horns or similar: Duct Seal - 5 Pound Block - ComputerCableStore.com
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
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