Modern Acoustic Materials
Modern architecture has opened up a world of possibilities for acoustic materials. In general, acoustic materials can be divided into three types; absorbers, reflectors and diffuses. There are many crossover materials that combine attributes of each,but these are really the basics. By far, absorbers are the most popularly utilized in commercial construction with uses from industrial spaces to music performance venues. In the past, available commercial absorption materials were mainly made from rock wool, mineral wool, wood woodland later fiberglass cores. Sometimes with a fabric or metal mesh cover. As time went on, acousticians realized that varying the density and thickness of the core could absorb (transfer sound energy to heat) different frequencies. This led to the development of the classic acoustic ceiling tile and wall panels that we still see today.
Other absorption mechanisms such as Helmholtz (think of blowing across a Coke bottle) and membrane types have been developed but these tend to focus on narrow bands of frequencies and very low frequencies. Very useful materials for problem solving.
Advances in commercial architecture drove the development of absorptive materials that could disappear or enhance the architect’s vision. Acoustic plasters, absorptive perforated wood and metals and later micro-perforated and micro-slit materials in woods and clear materials enhanced the available absorptive ‘acoustic pallet’.
Reflectors are basically inherent in any architectural space. Hard floors, walls and ceilings are all acoustically reflective surfaces. Reflectors use the same theory as light reflecting off a mirror. The angle of the light hitting the mirror is the same as the angle of the light reflecting off the surface. This is called a specular reflection. This type of material can be used effectively by curving or angling a surface. It’s still a specular reflector (not a diffuser). You see these surfaces commonly used in music venues.
Diffusive materials were commercially developed in the 1980’s using the pioneering work of Manfred Schroeder. The materials are distinctive in appearance by their deep wood wells and fins. The concept is to reflect sound energy throughout a room by changing the phase(time)and direction(spatial)of a sound wave through interference. Over time, many manufacturers have developed diffusive surfaces with some working better than others. Diffusive materials are commonly used today in recording studios and music venues.
As acoustic engineers our job is to combine these types of materials within the architect’s vision to maximize both the aural and aesthetics of a space.