Hajime Miura

An Estimation of Randomness of Scattering Media by Power Spectrum of Ultrasonic Scattering Wave

Two methods are shown for characterizing shapes of a power spectrum to estimate distribution (randomness) of the spacings of the scatterers. One method is FFT of cepstrum (FFTC). The other is fractal-based analysis which is useful for characterization of complex figures such as geometry. Using a one-dimensional scattering model, trial estimations of the randomness of the scatterers were performed, and it was found that the randomness could be discriminated by both methods.

Accuracy of pressure calibration of 1/2‐in. microphones up to 20 kHz

Specifications of both laboratory standard and measurement microphones are now defined in Parts 1 and 4 of IEC 1094 ‘‘Measurement microphones,’’ respectively. Methods for the absolute pressure calibration of these microphones are also defined in Part 2 of IEC 1094. These standards were published recently. In this report 1/2‐in. condenser microphones were used, such as LS2aP/LS2bP: MR112, B&K4180, and WS2P/F: various measurement microphones including those of sound level meters, have been calibrated up to 20 kHz using two couplers: plane‐wave and large‐volume. Calibration data are compared to each other and the accuracy of the calibrated results are discussed in detail.

Analysis of sound generation mechanisms of a Samisen: Comparison between its sound waveform and vibration waveforms of the skin, bridge, and plectrum at the beginning of the sound

A Samisen is one of the typical plucked string instruments in traditional Japanese music. In this work, the sound generation mechanism of the Samisen will be discussed by analyzing how each part of the Samisen works. The Samisen sound is classified into four time regions by considering the characteristics of the waveform. The time–frequency analysis of the vibration waveform of each part in each time region is compared with that of the sound. Furthermore, the sound generation mechanism will be discussed, including the time region by the transient touch of the plectrum to the strings and the skin. It is concluded that both the cause of the vibration of the skin and the generation of the Samisen original sound are mainly due to two mechanisms: the transmission of the continuous vibration of strings through the bridge and the transient and direct touch of the plectrum.

A Characterization of Ultrasonic Power Spectrum by Fractal Analysis–Imaging by Fractal Dimension–

The shape of the power spectrum of scattering wave is affected by position distribution of the scatterers (mean spacing and irregularity) constructing the medium. Fractal analysis is an appropriate tool for estimating this shape and gives us much information on the internal structures of the medium. This paper describes imaging experiments and an image obtained by the fractal dimension of the power spectrum. In the images obtained by this method it is easier to discriminate the different internal structures than in those obtained by conventional intensity imaging.

An estimation of absorption coefficients measured in a small reverberation chamber

This paper describes a simple and practical technique for measuring absorption coefficients of a material utilizing a small reverberation chamber. The chamber is used as a sound insulation box as well as a chamber for a reverberant sound field. The chamber does not have an ideal diffuse sound field but a sound field just for absorption measurements. A method based on the sound intensity technique using array microphones has been adopted to measure the absorption coefficients. Many loudspeakers are arranged in the chamber in order to improve the directivity distribution of the incident sound power near the surface of the absorbing material and m simulate a random incident sound field. Theoretical and experimental considerations regarding the effect of multiple sound sources in a small reverberation chamber and regarding the dependence of measured reverberant absorption coefficients on the distribution of sound power directivity are presented.

Transient latency in masking level difference

The threshold was measured for a signal S0 of 100 ms long at various timing points in a noise burst by a sequential searching procedure. The noise burst lasted from t = −1000 ms to t = 1000 ms. At t = 0 ms, the noise was changed from N0 to Nπ. The threshold was expected to decrease just after t = 0 ms. The latency was defined as a time constant of the decreasing characteristic of the threshold. In the case of S0 being a pure tone, the results showed artifacts at the N0 area and it was hard to define the latency. In the case of S0 being a vowel (female /a/, /i/ and male /i/), the latency was about 100 ms when subjects were required to identify the signal, and the latency was about 10 ms when subjects were required to detect the signal. The equalization and cancellation model could not explain the 10‐ms latency, because it is not reasonable to assume such fast feedback in the model. It is speculated that both the addition and subtraction of dichotic and/or diotic signals are sent to a higher level of the he...

A study on the standard for sound intensity measurement

A study on a traceability system for sound intensity standards required for accurate sound intensity measurements is described in detail. Required characteristics for the system, such as a calibration method for sound intensity meters involving a field calibrator and a working standard, are discussed. A free‐field calibration method using a progressive wave or a standing wave in an anechoic room is proposed. This is valid for the estimation of accuracies of intensity measurements in complicated actual sound fields. Some ideas on the generation of a calibrating sound field and a standard sound intensity probe are given. The standard probe is composed of several pressure microphones mounted on a rigid sphere and is precisely calibrated using a laboratory standard condenser microphone. To obtain enough accuracy in intensity measurements using the system, five sound intensity meters on the market were tested in various sound fields. The results show that the proposed traceability system is valid for sound int...

A characterization of the power spectrum of scattered ultrasound using a fractal‐based analysis

A method for extracting the characteristics of the power spectrum of ultrasound scattered from multiple scatterers using a fractal‐based analysis is presented. The shape of the power spectrum is usually very complicated. The shape contains structural information about the medium, because the shape depends on the internal structure of the medium. If the power spectrum of the scattered ultrasound has a fractal structure, characteristics such as self‐similarity and fractal dimensions are useful to characterize the power spectrum. When the scatterers are regularly arrayed, a high self‐similarity of the power spectrum will be expected. On the other hand, when the array is partially disordered, the sell‐similarity of the power spectrum will be lower. Fractal dimensions will be expected to relate to the mean distance between the scatterers. By numerical simulations and basic experiments, the validity of these ideas has been confirmed.

An automated coupler calibration system for laboratory standard condenser microphones

An automated coupler calibration system for laboratory standard condenser microphones is manufactured for trial use. Active couplers whose cylindrical wall vibrates as a sound source are designed. These couplers are used so as to get pressure response levels of microphones in a short time and to reduce manual transaction. A microcomputer controls the system, processes measured values, examines them, and stores final results in a diskette. In addition, many digital techniques are adopted for noise reduction and for the convenience of calibration. Accuracies were tested for 1‐in. condenser microphones, such as MR103, using a coupler which has the same dimensions as the 20‐cm3 a coupler. Pressure response levels calibrated by the system agree well with those calibrated by the ordinary precise coupler calibration system within 0.2 dB at the frequencies 100–10 000 Hz.