The device, created by technologists from North Carolina State University, also promises to require less material. This leads to a reduced cost as well as taking up far less space than diffusers currently in use in studios, concert venues and movie theaters. Sound diffusers are important for ensuring a good quality sound. Diffusion refers to the efficacy by which sound energy is spread evenly in a given environment. Optimally this is how perfect ‘surround sound’ is achieved. Here a perfectly diffusive sound space is defined as one where the acoustic properties are the same anywhere in the space. Surround sound is enriched through the use of additional audio channels from speakers, located strategically so they surround the listener and present a fixed or forward perspective of the sound field to the listener at a given location.
The effectiveness of a sound diffuser – the ‘diffusiveness’ of a sound field – are assessed by measuring the reverberation time
at various points within the given space (such as a cinema). These calculations are then used to find the standard deviation of the decay time.
The most common diffusers are called Schroeder diffusers. These have a limitation in that they are very bulky. The large size is needed since the size of a diffuser is a product of the wavelength of the sound it needs to diffuse. Here the depth of a Schroeder diffuser is about half of the wavelength of the lowest sound it needs to diffuse.
The new diffusers have an ultra-thin design, requiring a thickness that is just 5 percent of the sound’s wavelength. This means, for instance, instead of being 2 meters thick, a diffuser would only be 20 centimeters thick. The reduction in diffuser thickness has been made possible by the design of the individual cells in the diffuser. The ultra-thin diffuser consists of evenly spaced squares; with each of the squares an aperture leading into a thin, underlying chamber. The chambers have identical dimensions, although the size of the apertures varies. This allows for the the same sound diffusion to be achieved as per the much larger Schroeder diffuser.
The diffuser has been described in the journal Physical Review, in the paper “Ultrathin Acoustic Metasurface-Based Schroeder Diffuser.”
