Keys To Improve Architectural Acoustics: Sound Absorption and Diffusion

“Acoustics” in architecture means improving sound in environments. Although it is a complex science, understanding the basics – and making efficient and effective decisions – is much easier than you might think. The first step is to understand that there are two technical categories used in acoustics: soundproofing and acoustical treatment. Soundproofing means “less noise” and treatment, “better sound”.

Soundproofing is commonly used in music recording studios – but it can also be applied in locations near major avenues, schools, construction zones or even drummers’ neighbors. Soundproofing an environment is like protecting it against bad weather: the structure should be as solid as possible and without holes or cracks. To reduce the noise coming into and going out of a room, one must increase the structural mass of the walls, floor and ceiling, and seal the air gaps surrounding doors and windows, as well as the openings for refrigeration and electrical outlets. The extent of the measures taken will depend on how much noise there is on the outside, and how much you want it to be reduced on the inside.

On the other hand, sound treatments are used when you want to improve sound quality within an environment – for diners to hear and understand conversations at their tables in a restaurant, for students to understand teachers, for the whole audience to enjoy the music in an auditorium. All building materials have acoustic properties as they can potentially absorb, reflect or transmit sounds that reach them. When sounds are reflected, they cause an increase in the overall echo and reverberation levels in a space. When treating rooms correctly, echo and reverberation is reduced – and to treat rooms, there are two methods available: sound absorption and diffusion. The best treatment strategies combine these two techniques.

Sound absorption is defined as the incident sound that strikes a material that is not reflected back. An open window is an excellent absorber, since sounds that pass through the open window are not reflected back. Acoustic absorbers use materials designed for the purpose of absorbing sound that could otherwise be reflected back into the room. The more fibrous a material, the better the absorption, and denser materials are usually less absorbent. The acoustic absorption characteristics of different materials can vary significantly by frequency. In general, low frequency sounds are very difficult to absorb because of their long wavelengths. However, we are generally less sensitive to low frequency sounds, which means we often do not need to treat a room for low-frequency absorption.

Diffusion is the method of spreading sound energy with a diffuser to improve sound in a space. However, the process and tools of sound diffusion can be misunderstood, even by some professionals. Diffusion spreads the reflected sound energy in a room, also reducing the harmful effects of strong echo and reverberation. One type of diffusor is a curved panel, often with a fabric cover, which can be easily placed on walls and ceilings. These types of panels have the advantage of uniformly spreading flat-wall reflections that would otherwise be combined with original sound waves to create destructive interference. In a concert hall, for example, diffusion panels are used to enhance the richness of sound and help create a sense of spaciousness.

When a sound wave reaches an acoustic material, the sound wave vibrates the fibers or particles of the absorbent material. This vibration causes small amounts of heat due to friction and thus the sound absorption is performed by means of energy for heat conversion. For the majority of conventional acoustic materials, the density and thickness of the material affect the sound absorption amount and frequencies absorbed by the material. While the inherent composition of the acoustic material determines its performance, other factors may be used to improve or influence acoustic performance. For example, the incorporation of an air space behind an acoustic ceiling or a wall panel often improves low frequency performance.

By installing absorbers and diffusers in a space, the level of undesirable noise, in the form of echo and reverberation, is reduced. Noise is a relative term and can range from low levels of intrusive sound in a quiet environment to loud sounds in an already noisy environment. When noise levels are high enough, background noise can mask the speech sound levels that you want to hear. Restaurants can be classic examples of excessive noise interference due to lack of sound absorbing materials to prevent excessive build-up of echo and reverberation. Customers speak louder and louder to be heard and in doing so simply add to the noise. Proper acoustical treatments will helpreduce the accumulation of sound reflections and will reduce the need for customers to speak increasingly louder.

Being in an environment with inadequate acoustics can be extremely unpleasant and directly influences the environmental comfort of a space, our behavior, and even our productivity. Just as architects do not necessarily need be experts in every technical aspect of a project, it is the same for acoustical knowledge – it can be helpful to call on acoustical-product suppliers to carefully review the technical specifications of a project and to recommend the best available products to improve the acoustical environment.However, it’s also helpful to have a basic idea of these issues – it will help us make informed decisions for incorporating better sound within the project’s design, ultimately delivering a better user experience.


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