Arthur F. Niemoeller

Earphones in audiometry

The advantages and disadvantages of three types of earphones for audiometric testing are discussed. Supraaural earphones continue to be recommended for this purpose, in preference to circumaural and insert types.

Limitations on the Use of Circumaural Earphones

Published material on the calibration of circumaural earphones is briefly reviewed. The present lack of knowledge about these earphones and about the earphone‐to‐ear coupling is indicated, and the resultant limitations on the routine use of circumaural earphones in clinical and industrial pure‐tone audiometry are presented.

Use of a personal computer to model the electroacoustics of hearing aids

The electro‐acoustic behavior of a hearing aid receiver in an acoustic system similar to that found in many hearing aids was predicted by the method described by Egolf [D. P. Egolf and R. G. Leonard, ‘‘Experimental scheme for analyzing the dynamic behavior of electro‐acoustic transducers,’’ J. Acoust. Soc. Am. 62, 1013–1023 (1977)] using an inexpensive desktop computer.

Radiation Impedance of a Piston on Cohesive Soil

An experimental investigation was made to determine the mechanical radiation impedance of a rigid piston on the surface of clay soil. The force on and the velocity of the piston were measured to determine both the real and imaginary parts of the radiation impedance as a function of excitation frequency of the piston. Measurements were made for six different combinations of moisture and density of the soil, and results of these measurements are presented in graphical form. In the frequency range 50–200 cps, the load presented to the piston by the soil is essentially the same as would be presented by a mechanical compliance, the value of which varies with both moisture and density of the soil. The value of this compliance was computed for six different combinations of moisture and density. Second‐order dependence of compliance on moisture and density was assumed, and coefficients in a second‐order equation relating compliance to moisture and density were computed. The three‐dimensional surface that represen...

Evaluation of New Couplers for Circumaural Earphones

An experimental investigation of three couplers, suitable for testing circumaural earphones, was made to determine the limitations on their use. Two of these couplers were modified forms of standard U.S. couplers, the ASA‐type 1 and the NBS‐9A, while the third was a simple flat plate with a hole in which the test microphone is flush mounted. Results presented are based on tests made using the Telephonics TDH‐39 earphone with NAF‐48490‐1 cushion and the Philips model HA‐10 circumaural earphones. Below 2000 Hz, all three couplers are reliable and useful for measuring the responses of circumaural earphones. Above 2000 Hz, small variations in the electroacoustic system, defined by the earphone, cushion, coupler, and measurement microphone, cause large variations in the measured response. Variations in earphone responses are shown to be caused by variations in (1) earphones of a particular type, (2) cushions of a particular type, (3) applied force on the earphone, and (4) placement of the earphone on the coupl...

Reciprocity Calibration of Electroacoustic Transducers in the Time Domain

A method of directly evaluating the impulse response of a reciprocal electroacoustic transducer is presented. The method is essentially the time‐domain analog of the conventional (frequency‐domain) reciprocity method. The transient response of a coupled pair of identical transducers is used to compute the impulse response of either of the pair. A numerical method of obtaining solution is presented and is shown to be equivalent to the numerical solution of a real convolution integral equation. First, an approximate solution for one member of the pair of identical transducers is obtained. Then, a more precise solution is generated by minimizing the squared error between the actual response of the coupled pair and the one obtained by convolving the approximate impulse response with itself.The method was tried on two pairs of condenser microphones, the microphones within each pair being very nearly identical. A pair of Western Electric 640‐AA microphones were tested with the grids both on and off, and a pair ...

“Transition loss” From the practice room to the concert hall

The acoustical characteristics of music practice facilities are compared with those of some performance halls available at a university campus. Glaring quantifiable differences are observed between the practice spaces and performance spaces in terms of size, shape, reverberation, and interior construction schemes. Furthermore, the Perceived acoustical qualities of three performance spaces studied also vary greatly from each other, one being popularly referred to as “very reverberant and muddy,” another “dead,” and a third, “good.” The physical differences observed are presented, and their effect on the performance of music rehearsed in the small practice facilities and performed in the larger auditoria considered via subjective reports made by performers and listeners. These observations are further supplemented by an account of strategies employed by performers in adapting production to suit the different spaces, to compensate for the “transition loss” incurred in going from the practice room to the concert hall.The acoustical characteristics of music practice facilities are compared with those of some performance halls available at a university campus. Glaring quantifiable differences are observed between the practice spaces and performance spaces in terms of size, shape, reverberation, and interior construction schemes. Furthermore, the Perceived acoustical qualities of three performance spaces studied also vary greatly from each other, one being popularly referred to as “very reverberant and muddy,” another “dead,” and a third, “good.” The physical differences observed are presented, and their effect on the performance of music rehearsed in the small practice facilities and performed in the larger auditoria considered via subjective reports made by performers and listeners. These observations are further supplemented by an account of strategies employed by performers in adapting production to suit the different spaces, to compensate for the “transition loss” incurred in going from the practice room to the conc...

Amelioration of Deafness

Although medical advances will help prevent deafness and engineering developments may provide auxiliary resources, the primary responsibility for ameliorating this handicapping condition, particularly for children, rests on education. Available evidence suggests that the age of beginning educational intervention, including auditory amplification, language and speech development, and parent guidance, is extremely important—the earlier the better. Early education also requires procedures for identification of deafness. Some States have now legislated programs for children younger than five years, but much more remains to be accomplished.

Preliminary Studies of Voice Tracking Behavior

Each of a sample of 21 normally hearing adults attempted to match his vocal fundamental frequency to the frequency of tonal signals presented either before or during vocalization under a variety of conditions. He was never informed of his accuracy. The vocalizations were sustained for about 2 sec and were processed through a specially designed “pitch meter”and strip recorder with continuous output and fast rise time. In general, during the first 12‐sec of vocalization, the fundamental frequency shifted either up or down toward the target frequency. Subjects were within about 1% of the target frequency on approximately half the trials, although they showed a tendency to be “on target” for as many as 80% of the trials if they had been “on target” in the preceding trial. None of several measures of vocal pitch matching was related to the more classical auditory pitch matching.] This research was supported in full by a U. S. Public Health Service, Department of Health, Education, and Welfare research grant fr...

Soil Compliance as a Function of Moisture and Dry Density

Measurements of the compliance of class A‐6 soil as a function of moisture and dry density are presented. These measurements show that a recently published model, a three‐dimensional surface relating compliance to moisture and density, is invalid.