Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 59, Number 11
Friday–Saturday, October 17–18, 2014; Orem, Utah
Session B7: Acoustics I |
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Chair: Bonnie Andersen, Utah Valley University Room: Science Building 74 |
Friday, October 17, 2014 10:15AM - 10:39AM |
B7.00001: Development of Mid-Audio Thermoacoustic Energy Converter Invited Speaker: Orest Symko Mid-audio frequency thermoacoustic energy conversion shows much promise for a variety of applications where heat is converted to electricity. Recent developments of such devices have dealt with issues of tuning, array configuration, interfacing with heat source, and general optimization for raising the power output. In devices presented here, heat or waste heat is converted to sound when a sufficiently large temperature gradient is developed along a large surface area unit, called the stack, and it is located inside a quarter wave resonator. The heat-generated sound is coupled to an acoustic cavity where a piezoelectric device converts the sound to electricity. Operating at one atmosphere of air in the audio to ultrasonic frequency range of 2 kHz to 24 kHz, the quarter wave resonators are about 4 cm to 3 mm in length. Conversion of sound to electricity is by a PZT piezoelectric unimorph device. The electric load is either a resistor, or a set of LEDS, or a supercapacitor. Important issues that were addressed and studied were the tuning of the piezoelectric device to the heat engine (both are resonant systems), thermal coupling of the device to the source of heat (constant temperature or constant temperature temperature difference), impedance matching of various components, and synchronization for array configuration. The latter development is important because the devices are small handling relatively small powers even though they have high power density; synchronized multiple units provide considerable increase in power output. This has also led to the development of units operating in the ultrasonic range with heat engines volumes as small as 2.7 cubic millimeters. Although typically the power of a single unit has been low, a few milliwatts, all the fine tunings presented above have led to the development of heat to electricity converters which have significant power output. [Preview Abstract] |
Friday, October 17, 2014 10:39AM - 10:51AM |
B7.00002: Using helium as the working fluid to improve efficiency of high-frequency thermoacoustic engines Nathaniel Wells, Brian Patchett, Bonnie Andersen Previous work on thermoacoustic engines with bottle-shaped resonators has been done to improve performance by varying geometric parameters using air as the working fluid. This study is focused on transitioning from air to helium for the working fluid to further improve device performance. The theoretical ratio of efficiencies was derived for the two operating fluids. The existing engine was redesigned for evacuating the air and introducing helium into the resonator and six different types of heat shrink tubing used to hold the heat exchangers in place were tested for effectiveness with a vacuum and ease of removal. The optimal stack masses for this engine operating with air and helium were theoretically estimated and tested with air using six different stack masses from 50 to 62 mg. The resonator had a cavity with a length of 10 cm and ID of 4.13 cm and a neck with a length of 2.62 cm and ID of 1.91 cm and used steel wool for the stack material. The engine was supplied 12 W from a heating element applied above the hot heat exchanger in the neck and the acoustic pressure at the bottom of the cavity was measured. The optimal amount of stack in air was found to be 56mg and the acoustic pressure was 206 Pa, Pk-Pk. The adhesive heat shrink tubing was found to be the most effective for use with helium and ease of removal. [Preview Abstract] |
Friday, October 17, 2014 10:51AM - 11:03AM |
B7.00003: Speech Accommodation to Varying Acoustical Environments Mark Berardi, Timothy Leishman Differing acoustical environments can result in changes to voice use. This study aims to ascertain unhealthy speech accommodations (practices that may lead to voice disorders) that correlate with certain acoustical environments. Understanding of optimal talking environments will enable architectural acousticians to better prepare classrooms or other occupational settings for improved voice health. In this study we recorded native English speakers in an anechoic chamber and variable acoustics chamber at Brigham Young University. The participants were equipped with a head-worn microphone near the mouth and a microphone/accelerometer collar on the neck. They were recorded three times in both chambers with undisclosed changes to the variable acoustics environment. The three distinct conditions included changes to both the reverberation time and ambient noise. The results from preliminary analysis of the recordings will be discussed, including any gender-associated speech accommodation differences. [Preview Abstract] |
Friday, October 17, 2014 11:03AM - 11:15AM |
B7.00004: On the use of a real-time convolution system to study perception of and response to self-generated speech and music in variable acoustical environments Jennifer Whiting, Timothy Leishman, Eric Hunter A real-time convolution system has been developed to quickly manipulate the auditory room-acoustical experiences of human subjects. This system is used to study the perception of self-generated speech and music, and the responses of talkers and musicians to varying conditions. Simulated and measured oral-binaural room impulse responses are used within the convolution system. Subjects in an anechoic environment experience room responses excited by their own voices or instruments via the convolution system. Direct sound travels directly to the ear, but the convolved room response is heard through specialized headphones spaced away from the head. The development of the convolution system and future research regarding its use are discussed. [Preview Abstract] |
Friday, October 17, 2014 11:15AM - 11:27AM |
B7.00005: Measuring High-Resolution Directivity Patterns of Musical Instruments Joshua Bodon, Timothy Leishman, Daniel Slosky The directivity of a sound source describes its directional radiation characteristics. If the source is not simple, analytical predictions of directivity are very difficult. For complex sources, such as musical instruments, measuring directivity is often the simplest solution. However, several challenges arise when taking these measurements with sufficient quality and resolution. These include problems with assuring repeatability and consistent measurement conditions. Accordingly, musical instrument directivity measurement systems have implement only simple schemes and have generated low-resolution results. The research reported in this presentation involves the development and use of a measurement system in an anechoic chamber with 5 degree angular resolution (the highest resolution reported to date). Musical data for eight musical instruments have been recorded and both polar and balloon plots of directivity have been generated for the first five harmonics of every note of each instrument. Spherical near-field acoustical holography will be applied to collected data to produce sliced 3D solid balloon plots for directivity data at any radius beyond a minimum sphere, adding a third dimension to the directivity data. [Preview Abstract] |
Friday, October 17, 2014 11:27AM - 11:39AM |
B7.00006: Modeling of Helmholtz resonators for application in passive noise control Matthew Calton, Scott Sommerfeldt Acoustic resonators, such as the Helmholtz resonator, can be used to attenuate unwanted noise in a space. However, the classic Helmholtz resonator provides attenuation over a very narrow frequency band. This research aims to accurately model different resonator designs and to use those resonator models to investigate different configurations that can be developed to achieve a broader usable bandwidth. Using higher order approximations, more accuracy can be obtained in calculating the impedance and resonance frequency of a single Helmholtz resonator, which will then carry over into the overall configuration of the model. The impedance of a system of Helmholtz resonators in parallel is also considered, where the effects of acoustic coupling can be observed. [Preview Abstract] |
Friday, October 17, 2014 11:39AM - 11:51AM |
B7.00007: A two-point method for direct measurement of the room constant Zachary Jensen, Timothy Leishman The room constant is a key frequency-dependent value that is widely used to characterize reverberant fields. It is typically estimated from room boundary properties, viz., total surface area and average absorption coefficient. Unfortunately, these properties are often difficult to ascertain with sufficient accuracy. While reverberation times may be adequately measured using modern methods, the effective surface areas and volumes of many practical rooms are elusive. Furthermore, several formulations for the room constant exist without general agreement as to their best usage. This presentation introduces a two-point energy-based method that enables acousticians to feasibly measure the room constant without knowledge of the room volume, surface area, or average absorption coefficient. Numerical simulations illustrate the benefits of the approach. [Preview Abstract] |
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