Dynamat

[Steve O]

As a latecomer to the discussion, perhaps I can interject an observation?
I don't see anyone suggesting that the OP should totally eliminate fiber damping material and replace it with bitumen sheets.
The two obviously serve different purposes.

It's the assertion that bitumen sheeting serves no purpose at all inside cabinets, or is somehow only formulated to work on metal, that many comments are responding to.

Late to this too but wanted to point out that actual “dynamat” is a brand of damping material composed of a tacky butyl rubber on a thin aluminum sheet backing. Technically, butyl rubber is not bitumen and is more stable over the long term because it doesn’t harden and become brittle. Can’t speak to the other materials discussed.

Dynamat’s effectiveness is based on the well known principle of constrained layer damping. Also, the use of materials like bitumen and butyl rubber to damp vibrations (ringing) in wood speaker enclosures has historical precedent: the legendary BBC LS3/5a used bitumen as a panel damping material as required by BBC license.

 

[Steve O]

Seems like an odd use - I gather its like a 360 degree cup around the whole back of the driver.
Its hard to get the scale - how big is the driver?
And how does the back sound get out of the speaker frame?

Isn’t that a waveguide (horn - sorta) attached to a compression driver? If so, potentially a great use depending on material of construction of waveguide.

 

[45rpmspinner]

Late to this too but wanted to point out that actual “dynamat” is a brand of damping material composed of a tacky butyl rubber on a thin aluminum sheet backing. Technically, butyl rubber is not bitumen and is more stable over the long term because it doesn’t harden and become brittle. Can’t speak to the other materials discussed.

Dynamat’s effectiveness is based on the well known principle of constrained layer damping. Also, the use of materials like bitumen and butyl rubber to damp vibrations (ringing) in wood speaker enclosures has historical precedent: the legendary BBC LS3/5a used bitumen as a panel damping material as required by BBC license.

I stand corrected. And in looking further, I see that the other products mentioned are butyl rubber based as well.
Actually something I should've known as I worked with several variants/brands for 25 years.

 

[Poultrygeist]

Seems like an odd use - I gather its like a 360 degree cup around the whole back of the driver.
Its hard to get the scale - how big is the driver?
And how does the back sound get out of the speaker frame?

That's a 12" wave guide on a compression horn that's being dampened in this OB. A plastic wave guide can ring badly. There are two other 15" open back drivers per side in this build.

 

[hjames]

That's a 12" wave guide on a compression horn that's being dampened in this OB. A plastic wave guide can ring badly. There are two other 15" open back drivers per side in this build.

Thanks! Without anything of scale, no sense of the size, it looked like an encased woofer, which made no sense.
But as a waveguide - that makes sense.