Extraction of sound field information from high-speed movie of flowing dust

Abstract

In this paper, we propose a measuring method of the sound field using a high-speed movie of dust. The dust movement is considered to be related to the sound vibration. We observe the dust movement using two high-speed cameras in order to acquire information of the 3-D sound field. The influence of air current is reduced from the movement of dust so that the sound field information is extracted. The experimental results indicate that this method is effective for observing the sound field. Generally, a number of microphones are used for measuring sound fields. However, a sound field is affected by the presence of a microphone, which may have to be set at various positions. Various measuring methods of acoustic imaging and understanding are being studied today. For instance, a laser Doppler vibrometer (LDV) is used for measuring a sound field by observing the change in the sound pressure [1–3], and acoustic TV, which consists of a microphone array and a parabolic reflector, are used for the realtime measurement of sound source information [4]. However, the method with LDV needs the stationary sound played because the sound field must be scanned. The method involving the use of the microphone array and parabolic reflector cannot measure sound field information because its purpose is sound source observation. A high-speed camera is also used for observing the sound source and the sound field by particle imaging velocimetry (PIV) [5,6]. However, those methods require specific equipment such as spatially spreaded particles or a high-power laser. The purpose of this study is to obtain sound field information from a high-speed movie of dust. To measure the sound field more simply, we use the phenomenon of light reflection, for example, as when dust is visible in a theater spotlight. It is considered that knowing the dust movement enables us to observe the sound field particularly in particle velocities. We examine our method using high-speed movies of dust and comparison with the vibration of a speaker cone.