声场的直接测量

为准确测量声场分布,研究了基于激光测振仪的声场直接测量技术。基于声音在空气中传播时会引起空气折射率周期性变化的原理,利用激光测振仪测量了激光通过声场时激光光程受空气折射率的调制发生周期性变化产生的振动速度。由于声场在激光方向上的投影即为激光测振仪测得的振动速度,测量了声场在不同投影方向上的振动速度,再由Radon逆变换重构声场复振幅分布,从而实现了对声场的直接测量。文中实验测量了2kHz声场引起的振动速度振幅分布和相位分布,进而重构得到声压振幅分布和瞬时声压分布。测量得到空间分辨率为2cm,声压振幅最大为0.026Pa,对应的声压级为62.3dB。实验结果表明,基于激光测振仪的声场分布直接测量方法是可行的,该方法解决了现有麦克风阵列接触式测量声场存在的问题。

Direct measurement of sound field

To measure the sound field distribution accurately, a direct sound field measurement method based on a laser vibrometer is researched. Based on the fact that the air refractive index is changed periodically when the sound wave propagates in the air, the vibration velocity caused by the periodically changed refractive index occurred in laser passed through a sound field can be measured by the laser vibrometer. As the projection of the sound field in the direction of the laser is the vibration velocity, the direct measurement of sound field can be completed by measuring the projection of the sound field in different directions and reconstructing the complex amplitude distribution of the sound field using inverse Radon transform. The amplitude distribution and phase distribution of the vibration velocity caused by a 2 kHz sound field are measured experimentally, and the sound pressure amplitude distribution and the instantaneous sound pressure distribution are reconstructed. The measurement shows that the spatial resolution is 2 cm, the measured maximum sound pressure amplitude is 0.026 Pa, and corresponding sound pressure level is 62.3 dB. Experimental results indicate that the direct sound field measurement based on the laser vibrometer is feasible, and it solves the problem existing in the sound field measurement by using microphone arrays.