sebackman
12-30-2013, 07:42 AM
Dear all,
Maybe this is covered in posts before and if so you can stop reading here :-) .
I have experimented with damping of aluminum horns for a while with mixed success. Since JBL has moved on to new better acoustic materials I started to look into dampening Alu horns to potentially get rid of ringing in the alloy.
I have tested several alternatives including different kinds of painting with “noise cancelling coating”. Some of it made for acoustic treatment, some for treatment of sheet metal in cars and I also tried dampening coating for boats. -Non with really good effect.
I went over to try applying different “sheets” of dampening materials with mixed success. I tried several materials made for acoustic treatment, sheets for boats, sheets for cars and special adhesive “mats” from a guy that builds cars for db-racing. All with mixed effect.
They all had different results but the “best” of the pack was simple 5mm Bitumen sheets made for dampening of sheet metal in cars. The problem with them was to get them to stick to the outside of the horn.
After trying different application methods I decided to see if applying heat would make a difference. I cut the sheets to fit on the outside of the horn and by combining the adhesive on the sheet and some duct tape I applied them on the outside of the horn. Then I put the horn in the ownen for about 30-45 minutes at around 50-60 degrees to see if that would help the sheets to stick. Baked horn for dinner!
(please make sure any drivers come off first as magnets normally do not like heat!!)
The Bitumen and the glue got warm and started to bond with the horn but without hardening. I was worried that the “soft” texture of the Bitumen sheets would get lost and the dampening would be reduced, but it did not. I took them out and let them cool of in room temperature for an hour.
Now the Bitumen is formed as the horn and “bonded” to the horn surface in a way that gives excellent damping. This gave much better results than any of the experiments above and it was quicker and less greasy….
Attached are some pictures and also two simple Quicktime movies that shows ringing before and after dampening. Click on the links below to see/hear the difference. They are a bit large so it will take a few moments to load.
http://www.backman.eu/Public/JBL2332/2332 std.MOV (http://www.backman.eu/Public/JBL2332/2332 std.MOV)
http://www.backman.eu/Public/JBL2332/2332 dampened.MOV (http://www.backman.eu/Public/JBL2332/2332 dampened.MOV)
To my ears the sound is a little dryer and much more detailed and I perceive a clear improvement.
-But I will also put them in the measuring rig to see if there is a measurable difference.
Just my 25 cents.
Best regards
//RoB
Maybe this is covered in posts before and if so you can stop reading here :-) .
I have experimented with damping of aluminum horns for a while with mixed success. Since JBL has moved on to new better acoustic materials I started to look into dampening Alu horns to potentially get rid of ringing in the alloy.
I have tested several alternatives including different kinds of painting with “noise cancelling coating”. Some of it made for acoustic treatment, some for treatment of sheet metal in cars and I also tried dampening coating for boats. -Non with really good effect.
I went over to try applying different “sheets” of dampening materials with mixed success. I tried several materials made for acoustic treatment, sheets for boats, sheets for cars and special adhesive “mats” from a guy that builds cars for db-racing. All with mixed effect.
They all had different results but the “best” of the pack was simple 5mm Bitumen sheets made for dampening of sheet metal in cars. The problem with them was to get them to stick to the outside of the horn.
After trying different application methods I decided to see if applying heat would make a difference. I cut the sheets to fit on the outside of the horn and by combining the adhesive on the sheet and some duct tape I applied them on the outside of the horn. Then I put the horn in the ownen for about 30-45 minutes at around 50-60 degrees to see if that would help the sheets to stick. Baked horn for dinner!
(please make sure any drivers come off first as magnets normally do not like heat!!)
The Bitumen and the glue got warm and started to bond with the horn but without hardening. I was worried that the “soft” texture of the Bitumen sheets would get lost and the dampening would be reduced, but it did not. I took them out and let them cool of in room temperature for an hour.
Now the Bitumen is formed as the horn and “bonded” to the horn surface in a way that gives excellent damping. This gave much better results than any of the experiments above and it was quicker and less greasy….
Attached are some pictures and also two simple Quicktime movies that shows ringing before and after dampening. Click on the links below to see/hear the difference. They are a bit large so it will take a few moments to load.
http://www.backman.eu/Public/JBL2332/2332 std.MOV (http://www.backman.eu/Public/JBL2332/2332 std.MOV)
http://www.backman.eu/Public/JBL2332/2332 dampened.MOV (http://www.backman.eu/Public/JBL2332/2332 dampened.MOV)
To my ears the sound is a little dryer and much more detailed and I perceive a clear improvement.
-But I will also put them in the measuring rig to see if there is a measurable difference.
Just my 25 cents.
Best regards
//RoB