Excess low-frequency sound absorption of structural beam side arranged absorber in classrooms
Reverberation time at lowfrequency is an important factor in classroom acoustics,for the purpose,special low-frequency sound absorption character in classrooms was studied when sound absorber was mounted at the sides of structure beams.Absorber with two different depths were installed at the sides of structure beam in classrooms,and reverberation times were measured under each kind of absorption configuration.The actual absorption coefficients of absorbers under each situation were calculated with the Sabine formula,and compared with that of random incidence test values in reverberation chamber.The results show calculated sound absorption was much higher than that measured in reverberation chamber at low frequency bands,display an excess low-frequency sound absorption effect.Further analysis showed the low-frequency additional absorption starts at the high-low transition frequency of the room,proved the effect can be explained as room mode theory.An absorption coefficients ratio was defined to quantify the excess low-frequency absorption,and mathematical formula describing relation between the ratio and frequency was derived.Calculated results with the formula are in good agreement with that of measurement.
Low frequency absorptionExcess absorption effectBeam-side absorption
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