1. Evaluating the impact of acoustic impedance matching on the airborne noise rejection and sensitivity of an electrostatic transducer
Valerie Rennoll, Ian McLane, Adebayo Eisape, Mounya Elhilali, James West
2. Relationship between loudness discomfort levels and acoustic reflex thresholds in adolescents with attention-deficit/hyperactivity disorder
Alexandra Moore, Sydenstricker, S., Nagao, K.
3. Three-dimensional sound field estimation using multiple interacting rigid spherical microphone arrays
4. Acoustic Black Hole Optimization
5. Infant Ear Canal Modeling
Evaluating the impact of acoustic impedance matching on the airborne noise rejection and sensitivity of an electrostatic transducer
Valerie Rennoll, Ian McLane, Adebayo Eisape, Mounya Elhilali, James West
To capture sound from solid mediums, such as the human body or musical instruments, transducers designed for airborne sound pickup are typically used. Acoustic impedance mismatches between the medium and transducer decrease the energy captured and increase noise corruption. Here, we demonstrate the improved sensitivity and airborne noise rejection of an electrostatic transducer with an acoustic impedance matched to the medium of interest. The transducer produces an electrical response when mechanical vibrations compress the distance between an elastomer with patterned microstructures and a charged electret film. Using a statistical model generated through an I-optimal design of experiments, the elastomer is fabricated with a specific polymer and concentration of nanoparticles to possess a targeted acoustic impedance. Transducers containing elastomers with impedances in the range of 1 to 2.2 MRayls are assembled and characterized on simulators emulating the human body and a wooden instrument. The noise rejection is quantified using the coherence between the captured transducer signal and the simulated ambient noise. Sensitivities are similarly characterized by comparing the transducer signal and input simulator signal. With an impedance closely matched to the medium of interest, the transducer demonstrates a 2V/N sensitivity and 35 dB SNR improvement compared to an airborne transducer.
Relationship between loudness discomfort levels and acoustic reflex thresholds in adolescents with attention-deficit/hyperactivity disorder
Alexandra Moore, Sydenstricker, S., Nagao, K., Nemours Biomedical Research
Abnormal auditory sensitivity is common in patients with ADHD, however, auditory sensitivity issues have not been well-studied in ADHD. This study investigated auditory sensitivity in ADHD using psychological and physiological measures. A group of 13 adolescents aged 13 to 19 with a current ADHD diagnosis (ADHD group) and a group of 24 adolescents with normal development (control group) participated in this study. Acoustic reflex thresholds (ART) were obtained using pure tone stimuli (500Hz and 1kHz) and wideband noise. Each stimuli was presented to each ear from 56 dB to 104 dB in a 2-dB step. Loudness discomfort levels (LDL) were also obtained using two stimuli (500Hz and wideband noise) in each ear. ART and LDL were collected without daily stimulant medication in the ADHD group. Questions related to auditory sensitivity were obtained using the Adolescent/Adult Sensory Profile. Preliminary results indicated no significant correlation between ARTs and LDLs and between ARTs and sensory profile scores in both groups. We found a weak correlation between ARTs and some sensory profile scores in ADHD group. The results suggested a mismatch between ARTs and behavioral measures on auditory sensitivity. [Work supported by the ACCEL grant (NIH U54GM104941), the State of Delaware, and Nemours Foundation.]
Three-dimensional sound field estimation using multiple interacting rigid spherical microphone arrays
Shoken Kaneko, University of Maryland
Rigid spherical microphone arrays (RSMAs) have been widely used in ambisonics (Gerzon, 1973) sound field recording. While it is desired to combine the information captured by a grid of densely arranged RSMAs for expanding the area of accurate reconstruction, or sweet-spots, this is not trivial due to inter-array interference. Here we propose multiple scattering ambisonics, a method for three-dimensional ambisonics sound field recording using multiple acoustically interacting RSMAs. Numerical experiments demonstrate the sweet-spot expansion realized by the proposed method. The proposed method can be used with existing RSMAs as building blocks and opens possibilities including higher degrees-of-freedom spatial audio.
Acoustic Black Hole Optimization. Kayla Petrover, NSWCCD Code 724
Acoustic black holes have a tapering profile to create the idealized phenomenon of zero reflection. This phenomenon relies on geometry instead of dampers, so it is an ideal way to remove vibrations without increasing mass or surface area. They can attenuate acoustic and structural vibrations for applications in air, space, ground, and marine vehicles and can be produced in ducts, beams, plates, and wedges. The phenomenon entails wave propagation in an ideal medium where the profile tapers according to the power law shortening the wavelength and decreasing the wave speed. Consequently, the wave’s travel time goes to infinity so that it never reaches the termination and cannot be reflected– creating complete absorption. For the application of a circular duct, thin annular rings of inner radii decrease with the power law to control pressure levels. An infinite number of rings and a final cross sectional area of zero are needed to create an ideal acoustic black hole and is impossible to achieve. However, imperfections create scattering and other losses that increase damping performance. Therefore, various configurations need to be tested to tune parameters such as the amount, thickness, and spacing of tapering rings to produce minimal reflection across a frequency spectrum. Many solutions exist to remove excess noise in undesired places, though, none create total sound absorption. Acoustic black holes are receiving more attention for their ability to approach total absorption, though further development is needed to realistically create a metamaterial. Attempts at creating plates with embedded acoustic black holes face structural problems. Acoustic black hole ducts with lossy material for support may be a solution. The creation of a metamaterial that maximizes the use of acoustic black holes, which have very high sound absorption coefficients, will improve sound absorption capabilities. This research seeks to maximize sound absorption of acoustic black holes by studying the effects of size and distribution of cavities at proposed lengths and taper powers. The knowledge gained will be used to create arrays of miniature acoustic black hole while maximizing sound absorption to create an acoustic metamaterial. Similar attempts that failed used EMBEDDED acoustic black holes resulting in structural failures due to the removal of mass. DUCTS will avoid such problems since the Acoustic black holes have a tapering power law profile that shortens the wavelength and decreases the wave speed so the travel time approaches infinity; the wave never reaches the end and cannot be reflected or transmitted, but is fully absorbed. An acoustic black hole metamaterial made of layered arrays of miniature acoustic black holes with damping material for extra damping and support seeks to outperform all other damping strategies. Year 1’s deliverables are the theoretical and experimental models to optimize the dampened acoustic black hole. Year 2’s are the models of the layered mini arrays. The cross-sectional area of the propagation region tapers to zero with the power law. When the propagating wave interacts with the tapering geometry, its wavelength and wave speed also conform to the power law, decreasing its wavelength and wave speed so the travel time approaches infinity; the wave never reaches the end and cannot be reflected or transmitted, but is fully absorbed. The acoustic black hole duct uses annular rings to create this power law taper via a virtual cone surface. This research will investigate the impact of the cavity size and distribution at certain lengths and taper powers. Impedance tube testing will validate the results. The cross-sectional area of the acoustic black hole’s propagation region tapers to zero following the power law. When the propagating wave interacts with the tapering geometry, its wavelength and wave speed also conform to the power law. This shortens its wavelength and decreases its wave speed so the travel time approaches infinity; the wave never reaches the end and cannot be reflected or transmitted, but is fully absorbed. The acoustic black hole duct uses annular rings and cavities to create a virtual cone surface that tapers following the power law. This research will investigate the impact of the cavity size and distribution at certain lengths and taper powers. Impedance tube testing will validate the results.
Infant Ear Canal Modeling. Hannah Kurdila, Penn State University
It is unknown whether the sound levels achieved during MRI procedures cause acoustic harm to the neonatal patient. We do know, however, how such exposures affect adults. We hope to apply the body of knowledge surrounding adult reactions to loud sounds to the infant population by studying the differences between these two populations. In this presentation, I will focus specifically on the differences between sound propagation in the adult and infant ear canal and the implications for MRI safety.
Spheroidal ambisonics – a framework for spatial audio capturing using spheroidal microphone arrays. Shoken Kaneko, University of Maryland
Ambisonics is an established framework to capture and reproduce spatial sound fields based on the spherical harmonics representation (Gerzon, 1973). A generalization – spheroidal ambisonics – based on spheroidal wave functions is proposed for use with spheroidal microphone arrays. Analytical conversion from spheroidal ambisonics to spherical ambisonics is derived to ensure compatibility with the existing ambisonics ecosystem. Numerical experiments verify spheroidal ambisonics encoding and transcoding for spatial sound field recording. The sound field reconstructed from the transcoded coefficients has a zone of accurate reconstruction which is prolonged towards the long axis of a prolate spheroidal microphone array.