Acoustic Array Systems

9

Application Examples

This chapter presents several application examples of microphone arrays involving practical noise sources, including a scooter, IT equipment, a compressor, and a vibrating plate. The close-up view of the nearfield array used in the following experiments is shown in Figure 9.1. Thirty channels of ¼-inch condenser microphones are fixed on a stainless frame. Microphones are uniformly spaced with adjustable inter-element spacing. A PXI/NI® system equipped with LabVIEW® interface was employed for data acquisition and processing. Many experiments were performed in a semi-anechoic room. The details of examples will be given in the following sections.

Figure 9.1 Close-up view of the 5 × 6 rectangular array

9.1 Scooter: Transient Sources

In the following, a 125cc SYM scooter served as a more practical source to evaluate the NESI technique. The scooter is mounted on a dynamometer inside a semi-anechoic room. The rectangular array was placed in front of the scooter engine case. The array parameters are selected to be M = J = 4 × 4, d = d_f = 0.1 m = λ/2 for 1.7 kHz and L = d/2. The inverse filtering was carried out by using 16 × 16 = 256 channels of FIR filters, each filter of order 252. In a total, 256 × 252 = 64 512 multiplications are required for DC, which is rather ...