Modal analysis techniques applied to sound field representation

Abstract

In structural dynamics, modal analysis permits normal mode representation for vibrating structures by recording multiple transfer functions and letting a computer animate a simple harmonic oscillator approximation to display normal mode motion in an expanded time frame. This work shows an example of applying this technique to the representation of a sound field. Phase information is recorded by using the excitation source as a reference signal, monitoring the sound field with a microphone, and forming a transfer function of the two with a dual channel FFT analyzer. The method is illustrated by showing the sound field above and below the sound board of a grand piano, and in a vertical plane in the general direction of an audience.