Room AcousticsPhysical and Geometrical (Ray) Acoustics
The calculation of modes in a rectangular enclosure is simple. The modes become complex and sometimes unpredictable in rooms of different shapes. There are 3 types of modes: axial (two parallel surfaces contribute to the modes), tangential (4 surfaces) and the oblique mode (6 surfaces).
Sound Diffusion and Diffusers
Sound in an enclosure can be described as a diffused if the intensity of the sound energy is equal in every location of the room, or the sound energy flows equally in every direction. Many different factors can enhance the diffused sound. These factors include geometrical irregularities, absence of focusing surfaces, the distribution of absorptive and reflective elements randomly scattered through the space, and the existence of diffusing objects (furniture) or panels (diffusers).
Diffusing panels scatter the sound in all, or in certain directions depending on their type and geometrical dimension. A new type of diffuser is Schroeder diffuser (Quadratic-residue diffusers). Its diffusion characteristics do not depend solely on its geometrical dimensions but also on an array of wells with depths determined by a listed quadratic residue sequence.
Reverberation Time (RT)
Reverberation time is the time required for the sound level in the room to decay 60 dB, or in other words, it is the time needed for a loud sound to be inaudible after turning off the sound source. This concept is shown in the following drawing and in the "examples" page:
The calculation of reverberation time using Sabine or Eyring equations assumes that the sound in the room be diffused. In practice, RT equations are good enough to describe the sound build up and attenuation in the room. In the case where the sound in the room is not diffused enough, such as rooms with good absorption surfaces in some areas, or with an unusual shape (long and narrow, very low ceiling, or many different focusing surfaces), the RT calculation is not accurate. There is Fitzroy equation to correct the RT calculation for rooms with good absorptive surfaces on one (or more) axis of the room.
There are few conditions that a smooth-surface panel should meet to be considered a sound reflector. These conditions are illustrated in the following figure:
Acoustical simulation is a technique that assists the acoustical consultants in the evaluation of room acoustics or the performance of the sound systems. This acoustical program can simulate the sound as it would be heard after the project is built. This is called auralization.
The physical data of the room is entered into the program. AutoCAD file can be used to transfer the data to the program. The data entry includes surface materials, background noise, and the seating layout.
Some of the acoustical factors that can be studied in these acoustical programs include reverberation time, intelligibility, echo, and sound levels over the seating areas.