Material Testing

With today's growing focus on noise control issues and the emergence of sound quality as an important aspect of product design, acoustic material testing is becoming increasingly relevant to engineers, designers and manufacturers from a broad range of industries. Acoustic material testing is the process by which the acoustic characteristics of materials are determined in terms of absorption, reflection, impedance, and admittance.
There are many different methods to determine the acoustic properties of materials. They mainly involve exposing them to known sound fields and measuring the effect on the sound field caused by their presence. There is a range of standards covering material testing (e.g., ISO 10534-2, ASTM E 1050-98), prescribing well-defined acoustical conditions and special instrumentation to ensure accuracy and repeatability.

Acoustic Material Properties
Absorption Coefficient (a), where 0 < a < 1, the fraction of sound energy that is absorbed at any surface.

Complex Reflection Coefficient (r), where 0 < r < 1, the ratio of the pressure amplitude of the reflected wave to the incident wave.

Complex Acoustic Impedance (Z), where Z = R + jX [Pa x s/m³], the ratio of the surface sound pressure to the sound particle velocity through the surface.

Complex Acoustic Admittance (G), where G = g - jb [m³/(Pa x s)], the ratio of the sound particle velocity through the surface to the surface sound pressure.

Transmission Loss (TL), the ratio of the airborne sound power incident on the partition to the sound power transmitted by the partition and radiated on the other side [measured in dB].