Volume 17, Issue 2, October 1945
Index of content:
17(1945); http://dx.doi.org/10.1121/1.1916304View Description Hide Description
A former discussion of the theory of the Herschel‐Quincke tube is continued and supplemented by the investigation by Professor H. S. Uhler of a more general case. With the areas of the bifurcated conduits different, it is found that the number of frequencies giving zero transmission is again more numerous than determined by the condition of a difference of phase corresponding to that of one‐half wave‐length in the two branches. In the more general case the former fixed relations between these phase differences no longer holds. They are now connected by the equality , where S 2 and S 3 are the areas and α2 and α3 the phase differences in the corresponding branches.
A General Theory of Passive Linear Electroacoustic Transducers and the Electroacoustic Reciprocity Theorem. I17(1945); http://dx.doi.org/10.1121/1.1916305View Description Hide Description
A theory of the operation of passive linear electroacoustic transducers is developed on the basis of the most general linear equations (in this case, integral equations) relating the pressure and normal velocity at each point on the transducer surface and the voltage and current at the transducer's electrical terminals. These, together with the appropriate solutions of the wave equation expressed through the use of Green's functions for the medium in which the transducer is immersed and the equations defining the electrical termination of the transducer, completely characterize the behavior of the transducer and allow explicit calculation of such quantities as impedances, responses, etc., in terms of four parameters entering the fundamental equations.
On the basis of this theory, a proof of the reciprocity theorem for electroacoustic transducers relating their speaker and microphone responses is presented embodying the conditions necessary for its validity. These conditions are essentially the existence of certain symmetry relationships among the transducer parameters. When these symmetry relationships may be expected to hold is to be discussed in Part II of this paper to appear later. Some applications of the theory are presented and others are outlined.
17(1945); http://dx.doi.org/10.1121/1.1916307View Description Hide Description
An asymptotic expansion has been derived from a formula given by W. N. Brown, which allows the plotting of directional and response curves for a vibrating cone in an infinite baffle. The results are compared with those pertaining to a flat disk of same radius.
17(1945); http://dx.doi.org/10.1121/1.1916308View Description Hide Description
17(1945); http://dx.doi.org/10.1121/1.1916309View Description Hide Description
17(1945); http://dx.doi.org/10.1121/1.1916312View Description Hide Description
These specifications for methods of measurement of hearing aids were drawn up by a technical committee organized by the American Hearing Aid Association, including engineering representatives from most of the larger manufacturers of hearing aids as well as technical representatives from non‐commercial groups who have been working in this field. It is believed that these specifications represent the best of present practice, although additions may be made later to cover further material such as methods of applying correction factors for the baffle effect of the body of the wearer, for the difference between the pressure and the free field characteristics of the ear, and for possible leakage of sound between the ear and the ear insert, as well as standardized methods of measurement of instruments with bone conduction receivers and of carbon type hearing aids. Since sufficient information is not yet available to reach definite conclusions on these points, the code is offered in its present form for consideration by those interested in this subject.