What is anti-drumming?

What is anti-drumming?
If you are not familiar with the acoustic term anti-drumming, then you have probably never heard of it until now. Because anti-drumming is more often used than you might think. Anti-drumming is not only an acoustic term, it’s also the result of an application with products mostly refered to as 'bitumen damping sheets'. More about that later. The term anti-drumming is often used in the world of acoustics to explain the isolation of vibrations in rigid materials, such as sheet metal, polyester, aluminium, underlayment and plywood.

The most simple explanation, which most people will recognize, is the sound of a Gong. When a Gong is set in motion it produces a distinctive sound that lasts several seconds. But what happens when you firmly hold the gong? Practically nothing, the energy is isolated to the point of impact, and does not travel thru the surface of the gong, thus no Gong sound is produced. The acoustical term for this is, anti-drumming, the isolation of energy at the point of impact. The Gong-like effect also occurs in the hull of a ship, machine enclosures made of sheet metal, car doors when you close them, and the most common, were you might recognize anti-drumming from, the steel sink in your kitchen. Look underneath, almost certain there is a little black patch of anti-drumming.

How to insulate vibrations with bitumen damping sheets  
To reduce vibrations in a material we need to add weight to it, preferably at least half of the surface's weight, in such a fashion that this weight holds a firm grip to the surface that we want to insulate, as if it is holding a Gong. The best way to isolate vibrations throughout the whole surface of a material, a sheet of metal for example, is to apply a sufficient amount of mass and quantity on the right spot. Finding the right spot is fairly easy, this is the spot where most of the impact takes place, thus where the vibrations starts. In a ship’s hull this could be where the bow thruster is located.

The sufficient amount of product would be at least one and half meters around the location of the impact, or again in ship where the thruster is located. The right product, with enough mass and stiffness, depends on the thickness and weight of the material that we want to insulate. We can use this scheme to see which Vibraflex bitumen damping sheets to use on sheet metal:

• Sheet metal 1 to 2 mm: Vibraflex UF  5  kg/m²
  
• Sheet metal 2 to 3 mm: Vibraflex UF  8  kg/m²
  
• Sheet metal 3 to 4 mm: Vibraflex UF 10 kg/m²
  

Anti-drumming products for cars and other vehicles
For anti-drumming applications in cars, to insulate doors, floor or wheel arches to reduce driving noise, we usually recommend the boxed Vibraflex. These are easy to use pre-cut sheets with a strong adhesive. In the car audio world Vibraflex is also called 'deadener'.

Questions?
And as always, if you have any questions just let us know, we are happy to help you.