Directional Finding Array Technology
Based on the fact that sound travels at finite speed (approximately 340m/s) in the air and if there are at least 2 microphones spaced apart, the wave front impinges on each microphone at different time.
Fig 1 illustrates how sound wave arrives at different time at different microphones. Through digital signal processing techniques, the time arrival difference between different microphones can be estimated. With the time delay estimation, it is possible to derive the direction of sound source.
If more than 2 microphones are arranged in a specific layout, it is possible to tell if the sound source originates from the front, back, or side with respect to the position of the microphone array.
Fig 2 shows an example of 4-microphone array arranged in rectangle shape. Due to the specific layout, the array is able to estimate the direction of sound source 360° on the horizontal axis.
By having two arrays at known distance and if their relative position are also known, it is possible to estimate the distance of the sound source. The methodology is generally called triangulation.
Fig 3 illustrates the concept of triangulation.
We learnt in Fig 1 that direction of sound source can be estimated on the horizontal axis because the microphones are layout parallel to the ground plane. If an additional microphone can be placed on the vertical axis (Fig 4), it is then possible to derive the elevation angle of the object.
If the distance of the sound source is known through triangulation, the height of the object can also be estimated.
Product and Application
Based on BITwave’s direction finding technology, we’ve developed following products