The almost current sound localization methods do not have enough resolution in low frequency sound localization. To overcome this disadvantage, I am now developing the new sound localization method, Double Nearfield Acoustic Holography (DNAH) method. This method is a converted method of conventional Nearfield Acoustic Holography (NAH) method. In this proposing method, the resolution of low frequency sound localization is improved by using sound propagation information on doubled measurement planes. To prove the performance of proposing method, the basic experiments with variable conditions are conducted. In these experiments, the small speakers are used as sound sources. In this paper, to discuss the ability to apply to actual industry, the effect of measurement distance from the sound source is explained. Some experimental results with changing measurement distance are shown in this paper.
The experiments are conducted for a 100Hz or 40Hz sound source, and measurement distance of NAH and DNAH method are changed from 0.1m to 1.0m. In all experiments, the experimental results of proposing DNAH method show higher resolution than the results of conventional NAH method. However, with the distance larger than 0.6m, the reconstructed images by DNAH method do not show the enough resolution to localize the sound sources of mechanical products. In the images by DNAH method with the distance shorter than 0.5m, the sound source can be detected.
As a result, in the low frequency sound localization, the proposing DNAH method shows the better results than conventional NAH method, even if the measurement distance is not contacting distance.