Sound radiation from an acoustic source typically exhibits directional behavior, as is the case for the human voice, musical instruments, and loudspeakers, to name just a few. The necessity of directional data for many applications, such as sound source modeling, microphone placement, room acoustical design, and auralization, motivates directivity measurements. However, these measurements require careful understanding and implementation to produce the most meaningful results. Accordingly, this dissertation addresses several topics relevant to directivity theory, measurement, processing, and application. It first expands and amends previously published concepts of an acoustic source center and demonstrates the close relationship between the center and a source's far-field directional response. This relationship subsequently leads to an acoustic centering method that improves source placements within directivity measurement arrays. The dissertation then addresses several measurement considerations, including the required numbers of sampling positions for directivity measurements, quadrature rules applicable to standardized dual-equiangular sampling schemes, and a source's far-field response from arbitrarily shaped microphone arrays. Selected directivity results for the human voice and musical instruments illustrate applications of the developed measurement theories for procuring high-resolution results over a sphere. Compiled voice and musical instrument directivities now appear in an open-source database for use in room acoustical modeling, microphone placements, and other applications. To better elucidate and help predict sound source radiation, this work proposes several theoretical models, including equivalent point-source models, low-frequency radiation from a radially vibrating cap set on a rigid spherical shell with a circular aperture, and radiation from a vibrating cap on a rigid sphere with imposed mode shapes. Finally, this dissertation presents two microphone placement methods for audio and other applications. The first method approximates the measurement of a source's sound power spectrum through a single-channel measurement; the second considers microphone placement for maximum perceived loudness. The work's various developments, results, and conclusions will assist researchers and practitioners in better evaluating, predicting, and applying sound source directivities for many uses.

Currently in the United States, Active Noise Reduction (ANR) headphones cannot be tested and labeled as hearing protection devices (HPDs) due to inherent limitations with the existing psychophysical headphone testing standard, real-ear attenuation at threshold (REAT). This research focused on the use of a standard, for physical, microphone-in-real-ear testing, (MIRE, ANSI S12.42-1995), to determine if MIRE may be appropriately used to measure the total attenuation (i.e., passive + active) of ANR headphones. The REAT " Method B, Subject-Fit protocol," ANSI S12.6-1997(R2002), was also used to assess passive attenuation (and used for comparison with the MIRE data), as this is the current standard for passive Headphone attenuation testing. The MIRE protocol currently does not specify a standardized location for measurement microphone placement. Prior research is mixed as to the potential benefits and shortcomings of placing the measurement microphone outside versus inside the ear canal. This study captured and compared acoustic spectral data at three different microphone locations: in concha, in ear canal-shallow depth, and in ear canal-deep depth (with a probe tube microphone positioned near the tympanic membrane), using human test participants and five ANR headphones of differing design. Results indicate that the MIRE protocol may be used to supplant the REAT protocol for the measurement of passive attenuation, although differences were observed at the lowest-tested frequency of 125 Hz. Microphone placement analysis revealed no significant difference among the three locations specified, with a noted caveat for the probe tube microphone location at the highest tested frequency of 8000 Hz. Overall findings may be useful to standards-making committees for evaluating a viable solution and standardized method for testing and labeling ANR headphones for use as hearing protection devices. Microphone placement results may assist the practitioner in determining where to place measurement microphones to best suit their particular needs when using MIRE. Discussion includes an in-depth interpretation of the data, comparisons within and between each protocol, and recommendations for further avenues to explore based on the data presented. / Ph. D.

Research on microphone choice and placement has been previously made for a variety of instruments, such as drums, vocals, and guitar, to name a few. However, in comparison, very little research has been made on the bass-cabinet. With help of the different methodologies used for previous research on electric guitar and snare drum, the optimal placement and choice of microphone for a 4x10” bass-cabinet were investigated. In a listening test, pre-recorded basslines were mixed with other instruments since it is more common to hear it in a mix of instruments rather than listening to it by itself. To make sure that the topic is not too broad, focus on the genre of rock was taken for this investigation. Both qualitative and quantitative data were collected in a set of listening tests where the subjects rated their preference for their most and least preferable basslines. The subjects were asked to describe their preference utilizing different characteristics of the stimuli. An ANOVA test provided evidence that there is a statistical difference between the preference of one microphone model at a 15 cm distance from the bass-cabinet, in the category bass with band.