不等間隔配列形指向性音源の一設計法

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概要

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• Irregularly spaced arrays have been shown to be useful for wide-band directional sound sources because their highest signal frequency, which is limited by the frequency of the so-called "greating lobe" can be determined independently of the size of source elements and of the total length of the array which limits their lowest signal frequency. However, the procedure of realization of the optimum distribution of source elements has not been satisfactorily developed. In this paper a new approach to irregularly spaced array design is considered. It is based on distributing N individual source elements irregularly to the points which divide the total array length into M equal parts whose length is to be a shorter value than the shortest wave length of the signal. There are (N-1)!/2 arrangements of the source elements for given N and M. An arrangement which shows the maximum side-lobe reduction level may be the optimum arrangement. For N = 4〜6, the optimum arrangements and their side-lobe reductions are shown in Table 2 using ν_<mn> which is the space between the m'th and n'th source elements where the unit of ν value is one-M'th of the total array length. For more general N and M values, the expected value of side-lobe reduction of the optimum arrangement can be estimated. The estimation formula is given as R_<2δ> in eq. (12) and the estimated values are shown in Fig. 11. Finally, the usefulness of this design method is confirmed experimentally using three arrays. Array a) is the irregularly spaced array source (N = 5, M = 7) of which spaces of elements are shown in Table 2, array b) is the conventional uniformly spaced array source having equal total length to array a) and array c) is also an uniformly spaced array of which spaces of elements are equal to one-M'th of the total length of array a). As shown in Fig. 12, array a) can operate over the most wide frequency range because its lower limit is equal to that of array b) and its upper limit is equal to that of array c).

• 社団法人日本音響学会の論文
• 1974-05-01

著者

• 大賀 寿郎

  日本電信電話公社武蔵野電気通信研究所

• 大賀 寿郎

  Mix音研:芝浦工業大学

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