In this study, on-line microcomputer-aided visualization of mode shapes of vibrating surfaces is realized by the technique that the electrical signal corresponding the dynamic displacement detected by the gap sensor scanned over the vibrating surface is sampled digitally at the specific phase of the sinusoidal exciting signal. Whether it is a natural mode or not is determined uniquely by the existence of standing zero points at any phases of the exciting signal in 2-D plot.
In this method, mode shapes can be measured more accurately and at lower cost than the laser holographic interferometry. Also the real vibration shapes at the arbitrary phases and frequencies of the exciting signal is visualized. This system can be applied easily to the analysis of the vibration mode of the piano sound board, speaker cabinets, and the design of diaphragm and driving points of plate-speakers.