Development of surface area meter utilizing reverberation time

如果房间内的声场是扩散的，则房间的混响时间与房间的内表面积成反比。根据这一原理，可以通过测量放置物体的容器的混响时间来了解物体的表面积。在试验的基础上建立了一个实验装置，该装置具有实际混响室的缩小尺寸。带噪声从扬声器传输到容器中，声压由电容式麦克风拾取。使用噪声切换方法，测量了放置各种样品物体的容器的混响时间。实验结果表明：（i）由适度吸声材料制成的物体的表面积可以从混响时间得知;（ii）无论容器的形状如何，容器内的声场都没有充分扩散;（iii）容器的混响时间受到泄漏和周围条件的轻微变化的影响，例如大气温度和压力。至于由高反射材料制成的物体，从另一个实验中得知，测量容器的声阻抗的方法将工作得很好。一种新的设备正在进行中，它被精心设计以获得完全扩散的声场，并消除泄漏和大气温度和压力的影响。

The reverberation time of a room is in inverse proportion to the inner surface area of the room provided the sound field therein is diffuse. On the basis of this principle, the surface area of an object can be known from the measurement of the reverberation time of a container in which the object is placed. An experimental device was built on a trial basis which has the scaled-down dimensions of an actual reverberation room. A band noise is transmitted into the container from speakers and the sound pressure is picked up by condenser microphones. Using a noise switching method, the reverberation time of the container in which various sample objects were placed was measured. The experimental results showed the following : (i)the surface area of objects made of a material which absorbs sound moderately could be known from the reverberation time, (ii)the sound field within the container was not sufficiently diffuse in spite of the shape of the container ; (iii)the reverberation time of the container was affected by a slight change in the leak and the surrounding conditions, such as the atmospheric temperature and pressure. As to objects made of highly reflective material, it was known from another experiment that a method measuring the acoustic impedance of the container would work well. A new apparatus is afoot which is elaborated to attain a fully diffuse sound field and to eliminate the effect of the leak and the atmospheric temperature and pressure.