Interest In Acoustics Research Articles

Concepts in nonlinear acoustics: II. Implementations and Applications

The nonlinear (or parametric) array is of interest in acoustics primarily due to its superdirectivity; that is, its narrow beamwidth and extremely low side-lobe levels. The superdirectivity has an applicability in situations where reverberation or multipaths limit operation or when covertness is important. In this paper, the properties of a parametric beam are discussed and the importance of these properties to certain underwater operations is illustrated; a hypothetical system is designed to generate a parametric beam and is compared to two linear systems generating similar beams; and a partial list of present parametric sources is presented.

An Experiment in the Design of an Acoustics Course for Technical and Non-Technical Students

Students in engineering acoustics at The Pennsylvania State University proposed a new basic acoustics course for prospective graduate students in acoustics. Owing to the large number of departments with a growing interest in acoustics, and to the varying backgrounds of graduate students interested in acoustics, the course material was expanded to accommodate both technical and non-technical backgrounds. Structurally, the course is divided into two groups. Those with a mathematical background are taught along more technical lines, while those in other disciplines receive the same fundamentals qualitatively. The groups meet either separately, with the same instructor, or, when appropriate, simultaneously. This eliminates needless duplication of courses, interchanges viewpoints of students from different field areas, and consolidates manpower. The course, entitled Introduction to Acoustics, is being given for the first time this fall and its progress is reported.

The Intensive Difference Limen in Audition

In spite of its interest for acoustics, the intensive difference limen for sound has not been determined over a comprehensive range of frequency and amplitude. In the present experiment we have determined the difference limens for discrete intensive discrimination at five frequencies ranging from 128 cycles to 1000 cycles with intensities from 0.02 bars r.m.s. pressure to 3.4 bars (−65 db to −15 db). Both the physical conditions and the psychological judgment have been carefully controlled. The data yield a value for Δ db of 2.4 db in the middle range of intensities (−35 db to −15 db or 35 SL to 70 SL.)