2.3 Reverberation, Attenuation, Echoes and Sound Shadows Sound reverberation is the persistence of sound reflection after the source of the sound has ceased. Reverberation can have both a positive and a negative effect in architectural design. For example, specifying highly reflective ceiling panels directly above the stage area in an auditorium will help direct the sound toward specific seating areas, thus enhancing the room’s acoustical performance. However, that same reflective performance will become a negative factor if said highly reflective walls and ceiling materials are installed in the rear of the auditorium. That’s because the sound reflections from the rear of the room take too long to reach the audience, resulting in a distracting echo effect. When sound travels through a medium, its intensity diminishes with distance. In idealized materials, sound pressure (signal amplitude) is only reduced by the spreading of the wave. Natural materials, however, all produce an effect which further weakens the sound. This further weakening results from scattering and absorption. Scattering is the reflection of the sound in directions other than its original direction of propagation. Absorption is the conversion of the sound energy to other forms of energy. The combined effect of scattering and absorption is called attenuation. An acoustic shadow or sound shadow is an area through which sound waves fail to propagate, due to topographical obstructions or disruption of the waves via phenomena such as wind currents, buildings, or sound barriers. A short distance acoustic shadow occurs behind a building or a sound barrier. The sound from a source is shielded by the obstruction. Due to diffraction around the object, it will not be completely silent in the sound shadow. The amplitude of the sound can be reduced considerably however, depending on the additional distance the sound must travel between source and receiver. Sound reflection occurs when sound waves bounce off smooth, hard wall, ceiling and floor surfaces. Concave surfaces tend to concentrate or focus reflected sound in one area. Convex surfaces do just the opposite; they tend to disperse sound in multiple directions.
2.4 Issues of Acoustic Design Strategies Acoustical conditions in an enclosed space is achieved when there is clarity of sound in every part of the occupied space. For this to occur, the sound should rise to a suitable intensity everywhere with no echoes or distortion of the original sound, and with a correct reverberation time. Thus, these acoustical defects in buildings are important to recognize, diagnose and rectify. Acoustical reflectors or diffusers are implemented to evenly distribute the sound and to avoid areas where the sound quality is either weak, too excessive or cannot be heard clearly. Acoustic diffusion or sound reflection helps to provide a wider sound coverage for speech & music, and are often used to improve speech intelligibility and clarity in theatres, assembly halls, auditoriums, recording studios and classrooms. In addition to this, reflectors and diffusers are used to effectively reduce interfering reflections in any one direction by distributing the sound more evenly across the space.
Case study of Connexion@Nexus auditorium
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