Noise Absorption Principles

The elimination of reverberant conditions in an industrial space can result in a reduction of up to ten decibels in ambient noise levels. This may seem like a small amount, but even a minimal reduction in noise can bring dozens of workers into compliance with OSHA standards, and can prevent costly hearing conservation programs. Increased speech intelligibility also contributes to safety and productivity.

How do Noise Absorbers Work?

A typical steel wall or ceiling reflects almost 100% of the noise hitting it. Noise absorbers artificially simulate an open window or the open sky. An industrial noise absorber catches incident noise, channels and dissipates it thru its open porous structure and reflects back only a small portion.

When planning your Sound Proofing or Noise Control project please remember that  a noise absorber does not act like a vacuum cleaner... noise is not sucked up into the material. Noise is a wave bouncing off reflective surfaces at 750 mile per hour; it has to hit the noise control material in order to be absorbed. The actual noise reduction achieved  is a function of the surface area of absorbing material added to the room, and the existing noise absorption before the the noise control materials were added.

What makes a Good Noise Absorber?

The effectiveness of noise absorbers is an easy property to test for and compare. Absorbers are measured by a value called an Absorption Coefficient, æ, which is measured on a scale of from zero to one, with one being a perfect absorber (such as an open window). æ is measured at several different frequencies, and the average value is referred to  as Noise Reduction Coefficient, or NRC. The NRC is commonly used to compare materials to each other.

What is a Sabin? 

A Sabin is another unit of noise absorption that is used frequently in noise reduction calculations. A Sabin is simply the absorptive surface area times its absorptive surface area times its absorption coefficient (or its NRC).

Sabin =  æ X surface area ( in square feet)

For example, Our Sound Stopper noise absorbers have and absorption coefficient  (æ) of .065 at 1000Hz. Since each absorber has 16 feet of exposed surface area, we certify a minimum of ten Sabins of abortion per baffle for this product at that frequency. 

How much Noise Reduction can I get with Hanging Absorbers?

The amount of noise reduction you achieve is a function of the Sabins of absorption after treatment, divided by the Sabins that were there when you started. In practice, we have found that most customers can achieve a 4 to 7 decibel reduction in ambient sound pressure levels when hanging absorbers are installed in the recommended density of one absorber per 8-10 sq ft of ceiling area. The actual noise reduction, or noise control  you can achieve can be predicted with a fair degree of accuracy. Contact our Noise Control department for assistance with calculations for your sound proofing or noise control program