In this paper, we propose a physical model of the hi-hat. Two cymbals are modeled with thin spherical shells, into which a point mass resembling a stick collides. Two models are proposed for the collision of two cymbals: a spring model and an algorithmically mimicked inelastic collision model. The governing equations for the two proposed models are derived, discretized using the finite difference method, and analyzed numerically. Several numerical experiments have revealed the validity of the two proposed models and the characteristics of the hi-hat.

For applications in six-degrees-of-freedom (6DoF) content reproduction, this study investigates the angular resolution of radiation characteristics required to reproduce uttered speech in all three-dimensional (3D) directions as an angle at which humans are unable to perceive a difference in the comprehensive audio quality change between adjacent radiation directions. The radiation characteristics of uttered Japanese speech for female and male speakers are measured in three cross-sections, namely the horizontal, median, and frontal planes. The measurements are obtained using a spherical jig for 3D microphone arrangement. A subjective evaluation is conducted to clarify the impact of the difference in the radiation directions on the audio quality of uttered speech in each cross-section. Finally, a statistical analysis of the experimental results shows that the required angular resolutions are 30° relative to the horizontal plane, 30° relative to the median plane, and 60° relative to the frontal plane. Therefore, it is concluded that an angular resolution of at least 30° is required to reproduce uttered speech in all 3D directions.

The standard acoustic finite-difference time-domain methods often employ a transient input waveform as a sound source and introduce the waveform into an update equation of the sound pressure. There are three techniques to introduce the waveform: hard source, soft source, and transparent source. In the present paper, the advantages and disadvantages of these three techniques are firstly illustrated. Although the transparent source is most appropriate for obtaining an impulse response, an existing approach to achieve the transparent source requires heavy precomputation. To overcome this issue, the present paper proposes a computationally efficient approach for introducing the transparent source. It is derived from a mathematical investigation of the relation between an input source signal and the excited wave field. To validate the proposed approach, simple sound fields where diffraction effects can be ignored are considered, and the numerical results of the proposed approach are compared with those of the geometrical prediction. Furthermore, the proposed approach is applied to one- and two-dimensional situations for comparison with the existing methods. Computational efficiency of the proposed approach is shown, and some discussions on the difference of excited sound fields are provided.

Many predictive models of sound propagation in porous materials require flow resistivity as a parameter. In the case of fibrous materials, flow resistivity varies with bulk density (by forming) and is not necessarily an efficient parameter. On the other hand, only the material density and fiber diameter of fibrous materials are the physical quantities that do not vary with a change in bulk density. If one of these physical quantities is used as a parameter, since it does not vary with a change in bulk density and its measurement is not necessary, the acoustic design work (optimization of the fiber mixing rate) of fibrous materials would become possible. In this paper, the relationships of the material density and fiber diameter of fibrous materials with the normal incidence absorption coefficient are clarified, and a new predictive model is shown.