A Summary Report on Tests Conducted by the Riverbank Acoustical Laboratories Demonstrating Two Important Capabilities of Perforated Metals in Acoustical ApplIcations:
1. The Transparency of Perforated Metals When Serving as a Support or Protective Shielding for.Sound Absorbing Materials.
2. Their Capability in a Tuned Resonant Absorber to Attenuate Specific, Narrow Frequency Ranges.
Perforated Metals Serve Two Distinctly Different Functions in Acoustical and Sound Abatement Systems
1. The most common function of perforated metal in an acoustical system is to provide a supporting structure for sound absorbing materials such as fiberglass and in so doing. allow a maximum amount of the sound to pass through it to be absorbed. A noise reducing ceiling would be such a system. Of course, any of the offending sound that is reflected back into the protected environment would be defeating the system's purpose. So, what is desired in such a system is maximum transparency in the structural material.
2. Perforated metal's other function in acoustical systems is to provide tuned resonant sound absorption. In this function. the size and spacing of the holes in the perforated metal sheet in combination with its distance from a rigid back-up wall and intermediate sound absorbing materials can be designed to attenuate sounds within a narrow range of frequencies.
The tests reported on here were concerned with both of the above mentioned functions. They were conducted for the Industrial Perforators Association by the Riverbank Acoustical Laboratories to validate data developed by Theodore I. Schultz, Ph,D.* and presented in his book, ACOUSTICAL USES FOR PERFORATED METALS, published by the Industrial Perforators Association. The objectives of the tests were:
a. Determine which perforated metal specifications would provide a high degree of sound transparency.
b. Demonstrate the theories regarding Tuned Resonant Absorbers set forth by Dr. Schultz.
What follows is a summary of the results of these tests with illustrative charts.
*Dr. Schultz's many friends, clients and acoustical engineering colleagues were deeply saddened by his untimely death in August, 1989. His important contributions to the science of acoustics will be long remembered and appreciated.
