Acoustics

The acoustics of a space are characterized by the interaction between sound and a room, either by absorption, reflection, or diffraction by the walls.

Acoustic absorption refers to a material, structure or object absorbing sound energy when sound waves collide with it, as opposed to reflecting the energy. Reflection, on the other hand, is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Finally, diffraction refers to various phenomena which occur when a wave encounters an obstacle or a slit. It is the apparent bending of waves around small obstacles and the spreading out of wabes past small openings.

Acoustic metamaterials are artificially fabricated materials designed to control, direct, and manipulate sound waves as these might occur in gases, liquids, and solids. The science of building acoustics analyzes noise transmission from building exterior envelope to interior and vice versa. The main noise paths are roofs, eaves, walls, windows, door and penetrations.

The science of controlling a room’s surfaces based on sound absorbing and reflecting properties is called interior space acoustics.  Reflective surfaces can be angled and coordinated to provide good coverage of sound for a listener in a concert hall or music recital space. Ideal acoustical panels are those without a face or finish material that interferes with the acoustical infill or substrate. Fabric covered panels are one way to heighten acoustical absorption, as well as perforated metal. Finish material is used to cover over the acoustical substrate, this usually consists of fabric, wood, or acoustical tile.

The three main ways to improve workplace acoustics and solve workplace sound problems is by absorbing, blocking, and covering up.

Modal Theory

Geometric Theory

For rooms of high volume or with a complex geometry, the theory of acoustical geometry is critical and can be applied. The waves are modelised with rays carrying acoustical energy. This energy decrease with the reflection of the rays on the walls of the room. The reason of this phenomenon is the absorption of the walls.

The problem is this theory needs a very high power of calculation and that is why the theory of Sabine is often chosen because it is easier.

Sabine Theory

The Jay Pritzker Pavilion designed by Frank Gehry in Millenium Park in Chicago, is one of my favorite projects involving acoustically designed architecture. The venue has a system that effectively produces an even quality of sound throughout the entire venue. It has received critical acclaim for its technological adaptations, such as signal processing.

The overall acoustic system is a distributed sound reinforcement system, which allows musicians on stage to hear each other clearly in a way that facilitates ensemble play. In addition, direct natural sound from the stage is reflected from architectural surfaces as well as being reinforced by two sound systems. Distributed speakers allow for lower sound bolumes than would be necessary with centralized speakers.

In addition, I recently visited Carnegie Hall and admired the overall spherical shape of the interior hall in which the performances took place. This shape made the sound travel from the performer to every member in the audience, regardless of where they were sitting.