教室梁侧吸声的低频附加吸声效应

Excess low-frequency sound absorption of structural beam side arranged absorber in classrooms

为获得改善教室低频混响时间特性的吸声处理方式,该文对安装在学校教室梁侧边的吸声结构低频段的吸声特性进行了研究。通过将两种不同深度的吸声结构分别安装于教室结构梁的侧边,测量获得不同安装条件下教室内的混响时间,再根据赛宾公式计算得到吸声结构在教室的计算吸声系数,并与其在混响室测量得到的吸声系数对比。结果表明,根据教室实测混响时间得到的计算吸声系数在低频段远高于混响室测量得到的结果,呈现出低频附加吸声的特点。进一步分析得出了产生低频附加吸声效应的起始频率为房间的高低频转换频率,说明低频附加吸声来源于模态声场的影响。提出了用吸声系数比来定量描述低频附加吸声效应,给出了其数学表达式,并验证了计算与实测结果有较好的相符性。

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.