We observe that our experimentally measured emission power enhancement of a speaker inside a previously proposed metacavity agrees with our numerically calculated enhancement of the density of states (DOS) of the source-cavity system. We interpret the agreement by formulating a relation between the emitted sound power and the acoustic DOS. The formulation is an analog to Fermi's golden rule in quantum emission. The formulation complements the radiation impedance theory in traditional acoustics for describing sound emission. Our study bridges the gap between acoustic DOS and the acoustic Purcell effect for sound emission enhancement.

The Doppler effect is a common principle in all types of waves when sources and receivers have a relative motion. In acoustics, there are scenarios where sound sources rotate and produce the Doppler effect. These scenarios include sound produced by a speaker with a rotating horn and by the rotational motion of helicopter blades and airplane propellers. In this study, we experimentally measure the frequency shift due to a rotating sound source. A buzzer (2.8 KHz) is set to rotate at a fixed radius (75 cm) with the rotational velocity (60 rpm) controlled by a stepper motor. The radiated sound signals are recorded by a microphone at different locations. Spectrograms of the recorded signals display a shift from the buzzer’s original frequency. The shift oscillates with the period of the source rotation. We characterize the dependence of the shift on the position of the microphone. A formula for the shift is derived and is used to compare with the measurements. Our measurements and analyses gain insight into the Doppler effect due to a rotating source.

Binaural-dummy-heads are often used as standard measurement devices where modeling of the human binaural hearing system is desired. The binaural-dummy-head imitates a human head (and torso) which is used in binaural recording as well as research areas such as hearing aids, sound localization, noise measurements, etc. Commercially available binaural heads are not economically efficient for some purposes. This paper outlines a less expensive binaural dummy head built using ANSI/ASA S3.36-2012 standard as a reference as part of an independent coursework. A hard plastic mannequin was used as head and torso, and the two ears were real human ear replicas casted out of water-based alginate gel. The complex Head-Related Transfer Functions (HRTF) of our dummy head were measured in an anechoic chamber to evaluate its spectral and directional properties and were compared to the same properties of the standard commercial dummy head.

On a daily basis, individuals perform a variety of tasks in complex acoustic environments that contain background noise and reverberation. Previous research has demonstrated that, when tested in a laboratory setting, background noise and reverberation impair speech recognition and disrupt cognitive processing. These detrimental effects are especially pronounced for young children, older adults, and individuals with hearing loss. However, the specific environmental and individual factors that account for performance declines in the presence of background noise and reverberation, and whether these relations are generalizable to real-world complex acoustic environments, remains poorly understood. In the present study, children and adults performed speech recognition and speech comprehension tasks amidst background noise and reverberation in a state-of-the-art virtual sound room (ViSoR). ViSoR contains a Variable Room Acoustics System, which simulates the acoustic properties of real-world environments in a free-field test setting. Participants also completed standardized measures of attention, auditory working memory, and receptive vocabulary, which will be used to quantify the extent to which individual factors contribute to the observed changes in speech recognition and comprehension. Together, the findings from this study will provide additional insight as to the factors that underlie individual susceptibility to the detrimental effects of background noise and reverberation.

Efficient emission of directional sound waves is critical in imaging and communication, yet is held back by the inefficient emission at low frequencies, especially for a small source. A subwavelength enclosure with degenerate Mie resonances was implemented to experimentally enhance the sound power emitted to the far field where the radiation directivity pattern is preserved [L. Maryam et al., Physical Review Letters 120 (11), 114301, 2018]. When considering the efficient emission of directional sound waves, a subwavelength meta-cavity of hybrid resonances can be used to convert the monopole sources to multipole emission [X. Fan et al., Physical Review Applied 9 (3), 034035, 2018] or Mie resonances with spatial asymmetry can be used to even emit directional sound beams [J. Zhao et al., Scientific reports 8 (1), 1018, 2018]. The work offers a practical path toward applications that demand miniaturization of speakers for efficient emission.