New signal processing developments for low cast near-field acoustical holography systems

Most noise field viewing techniques involve utilization of expensive equipm ent. Implementing a powerful system obviously commands substantial developm ent and procurement of funds. Near-field acoustical holography (NAH) applic ations may be adapted for a small laboratory's budget. However, special com puter techniques must be implemented to overcome inherent constraints, such as a limited number of microphones and data acquisition channels, as well as an imperfect phase match of the microphones. A low-cost, PC-based, NAN s ystem was constructed and specific associated signal processing techniques were developed and tested. Phase error tolerances over the microphone grid were identified. Amplitude and phase calibration procedures were elaborated . Reconstruction of simultaneous 64 point measurements from four, 16 point grid positions was performed by using a reference microphone and data matri x manipulations. A new two-dimensional space window and filter were impleme nted, tested, and compared for energy leakage reduction, This paper describ es the development, implementation, and assessment of the resulting low-cos t NAH system, Possibilities for further development of the system are also discussed. (C) 1999 Institute of Noise Control Engineering. [S0736-2501(99) 00401-4].