Inter-reflection, standing waves and reverberation - Standing waves are stationary fluctuations in pressure due to the superposition of sound waves moving in the opposite direction.In this frequency region sound transmission is said to be coincidence controlled When the bending wavelength of the panel is equal to the trace wavelength then transmission increases and insulation is decreased. This is termed resonance controlled insulation.Ĭoincident sound - Not all sound striking a panel will strike this at right angles but some will strike this obliquely and these will produce a forced motion in the panel (the trace wavelength). Rigid panels - if a rigid panel is struck it will continue to vibrate at frequencies determined by its size, shape, and thickness - this is its "natural frequency" (natural mode of vibration).Īll subsequent frequencies which produce such vibration are called resonant frequenciesĪnd sound insulation will be reduced.In this part of the frequency range insulation is termed stiffness controlled. resistance to deformation) may have more effect than its weight. Panel stiffness - at very low frequencies the stiffness (i.e.increased frequency of incident sound decreases sound transmission.Īpart from just mass of the panel other factors can affect sound transmission: increased weight per unit area of panel decreases sound transmissionĢ. The panel will be vibrated by both direct and reflected sound waves.ġ. The sound does not actually penetrate the material but rather causes this to vibrate and act as a sound source itself. Panel resonance - Sound waves can propagate "through" a solid material by panel vibration.Primary reflection - Angle of incidence = angle of reflection, plus nature of sound reflector is important.Such problems can occur in auditorium with balconies. However, because of edge diffraction some sound will creep into this but such penetration is frequency dependent - high frequencies are lessĭiffracted than low frequencies. Sound shadow - Any barrier interrupting a sound wave will create a shadow (light).Edge diffraction - Edge diffraction results in the curvature of part of a sound wave around the edge of a barrier.Dispersion of modeled surface - Reflections can be reduced by making one surface dispersive i.e.Reflection from re-entrant angle - Sound entering right-angled corner of room will be reflected back towards source if surfaces are acoustically reflective.Surface absorption of direct and reflected sound. The way in which sound behaves in an enclosed space depends on the following factors: Shape, dimensions, construction, and contents of any room will determine how sound is transmitted, reflected and absorbed. DEA3500: Ambient Environment: Room Acoustics ROOM ACOUSTICS Behavior of Sound in an Enclosed Space
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