Shigeru Yoshikawa

Vibration of two concentric submerged cylindrical shells coupled by the entrained fluid

The vibrational characteristics of a point‐driven ‘‘double shell’’ (two concentric submerged cylindrical shells coupled by the entrained fluid) are investigated theoretically and experimentally. Of particular interest are the shielding effects, if any, of the outer shell upon the inner shell. The theory on the double shell is based on Flugge’s infinite‐shell equations, the Helmholtz wave equation, and boundary conditions at the fluid–structure interfaces. This theory is used to model a finite double‐shell structure in wave number‐frequency space. Experiments are carried out in which generalized near‐field acoustical holography (GENAH) is employed to provide the experimental vibration characteristics in wave number‐frequency space of the finite double shell. It is confirmed theoretically and experimentally that the outer shell of the double shell exhibits two separate dispersion curves: A higher‐frequency dispersion curve exhibits in‐phase vibrations with respect to the inner shell, and a second lower‐freq...

Acoustical behavior of brass player's lips.

The controversial problem of whether a brass players lip movements are best modeled as outward striking or as upward striking is approached by measuring the phase difference between mouthpiece pressure and lip displacement. In analogy with the phase of the input impedance to a resonant system, the negative/positive value of this phase difference suggests an outward-striking/upward-striking oscillation. On the basis of this speculation, the experimental results revealed the following: (1) Large lip-driven pipes support both outward-striking and upward-striking oscillations because of the lips high flexibility in the absence of a mouthpiece; (2) mouthpiece-nonresonant tube systems almost support the outward-striking oscillation over a wide frequency range; (3) mouthpiece-resonant tube systems totally support the outward-striking oscillation; (4) the French horn and trumpet exhibit the outward-striking oscillation for the lowest mode and the upward-striking oscillation for higher modes. The oscillation transition in brass instruments, which corresponds well to the change of mouthpiece pressure waveform from a low-pitch, nonsinusoidal one to a higher-pitch, more sinusoidal one, depends mainly on the nonlinear acoustic impedance of the lip opening. If its magnitude is negligible, the cavity coupling between the mouthpiece cup and players mouth yields a capacitive input impedance that favors the outward-striking oscillation; if its magnitude is significant, the cavity decoupling is likely to yield an inertive input impedance that favors the upward-striking oscillation. Since both the time-varying Bernoulli pressure at the lip opening and the area receiving this pressure are generally apt to increase as the blowing pressure increases, the upward-striking oscillation tends to dominate higher mode tones in brass instruments.

Jet-wave amplification in organ pipes

The amplification factor of an air jet waving over the mouth is estimated from flow visualization of the smoked jet, where the velocity ranges from 7–33 m/s, the Reynolds number from 1000–5000, and the sounding frequency from 130–580 Hz. The jet length is 15.8 and 10.2 mm in two models, while the jet thickness is 2.2 mm in both. The estimation is carried out by comparing the visualized envelope of jet waves with a simplified theoretical one. The envelope is visualized by the OR summation of the digitally memorized frames showing the instantaneous deflection taken with a speed of 1440 frames per second. Furthermore, the strength of mouth field defined as the acoustic displacement amplitude is derived from the envelope‐based estimation. A hot‐wire anemometer is then applied to measure this mouth‐field strength, whose value shows a good agreement with the estimated result. The amplification factor of organ jets was estimated as 0.26 to 0.18 (1/mm); the mouth‐field strength as 0.5 to 1.5 mm. A nondimensionalized representation of the relation between the amplification factor and the blowing velocity in our organ‐pipe jets roughly agrees with the theoretical curve based on the linearized spatial analysis of jet instability.

Measurement of structural and acoustic intensities using near-field acoustical holography

A non contacting method for measuring structural and acoustic intensities is proposed by developing the signal processing in near-field acoustical holography (NAH). The effectiveness of this method is illustrated by applying it to the measurement of radiation from ribbed and unribbed submerged plates. The spatial derivatives for determining the structural intensity are evaluated by a K-space filtration method newly developed by the authors. The experimental data obtained at 928 Hz and 1464 Hz are selected for specific and detailed investigation. The attached ribs have a small influence on the structural intensity flow at 928 Hz, so the vibrational mode of the ribbed plate is the same as that of the unribbed plate. However, since the attached ribs control the direction of vibrational energy flow at 1464 Hz, the vibrational mode of the unribbed plate is markedly changed.

Application of Generalized Near-Field Acoustical Holography to Scattering Problems

Generalized near-field acoustical holography (GENAH) is applied to scattering problems, making use of its wavelength-limitation-free characteristic in the reconstruction process. GENAH signal processing is directly adapted for the reconstruction of the scattered field, while a method to extract the scattered-pressure hologram is independently proposed to create scattering GENAH. The measurement of the near field of a scatterer yields the superimposed incident and scattered fields. Their decomposition is carried out by subtracting the incident-pressure hologram from the superimposed-pressure hologram in K space. The validity of this decomposition method was demonstrated by comparing the experimental and theoretical results of finite submerged shells. Reconstruction of shell-surface vibration induced by scattering displayed a reasonable result.

Acoustical characteristics of Chinese stringed instruments and their Asian relatives

In Asia, there are many relative musical instruments that derive from the same origin or share a similar structure. In spite of their similarities, they show distinct differences from each other in terms of their musical usages, playing techniques, and acoustic effects. This varies with each musical genre, musical structure, social background, and acoustic taste swayed by those elements. People often add special devices to musical instrument or improve them so as to realize their acoustical ideas. For example, the shamisen and biwa, Japanese plucked lutes, have devices to allow strings to vibrate against the neck‐wood, creating a reverberant high‐frequency emphasis called sawari, which is of special value in each performance. A device that creates a similar effect, called jawari in Hindi, is also found in the sitar, a traditional stringed instrument of India. On the other hand, the Chinese sanxian, one of the relatives of the Japanese shamisen lacks this device. In this presentation, specific features of ...

On the modeling of self‐oscillation in brass instruments

It is recognized that the lips of brass players vibrate two‐dimensionally, i.e., in parallel and perpendicularly to the direction of the air flow as the excitatory source. This two dimensionality gives two different models of lip motion in brass instruments: (1) the parallel model as a “reed striking outwards,” which is the reverse to the model of a woodwind reed as a “reed striking inwards” [N.H. Fletcher, Acustica 43, 63–72 (1979)], and (2) the perpendicular model as a “one‐mass vocal cord striking laterally” [J. Saneyoshi, H. Teramura, and S. Yoshikawa, Acustica 62, 194–210 (1987)]. The phase difference between the lip displacement and the acoustic pressure acting on the lips, or the frequency difference between the antiresonance of the horn itself and the sound excited, can determine which model is actually dominant. This paper describes some attempts to find these quantities on a cylindrical pipe blown by lips without a mouthpiece. The discussion of the experimental results and the modeling of the li...

Nonlinear wall vibration and wave steepening contributing to tonal metallicness and brassiness in a horn

It is well known that wave steepening and shock-wave formation due to nonlinear propagation through the bore are responsible for tonal brassiness of brass instruments. On the other hand, penetrating metallic tones are produced by hand-stopping the French horn. The present study demonstrates that the mechanism account for tonal metallicness of the French horn is nonlinear wall vibration of the bell. The measured waveforms of radiated pressure of the stopped tones indicate rapidly corrugating changes, which are not observed in brassy tones. Also, their spectra show much larger amplitudes of higher harmonics than those in normal mezzo-forte playing. The measurement of the wall vibration at the bell in hand stopping demonstrates similar characteristics. These results suggest that the bell wall vibration is responsible for the radiated tone color. Excitation experiments on the bell are carried out to elucidate the mechanism how the higher harmonic vibration is generated in hand stopping. They indicate that wal...

Changes in acoustical design from ancient shakuhachi to modern shakuhachi

The shakuhachi was originally introduced from China in the Tang dynasty around 750. Since this ancient shakuhachi has been preserved in the Shousouin of the Toudaiji temple, it is called the “Shousouin shakuhachi”. This shakuhachi, which has six tone holes to play a Chinese diatonic scale (e.g., A-B-Db-D-E-Gb-A, D-E-Gb-G-A-B-D), was adapted to play a Japanese pentatonic scale (D-E-G-A-B-D) by removing the second tone hole (Gb) around early 16th century. Moreover, the positions of five tone holes were modified to make effective use of the pitch bending (e.g., Eb) by drawing down players jaw and half-covering the tone hole(s) around the 17th century, and a scale pattern D-F-G-A-C-D was established. Since this shakuhachi (made from the root end of bamboo) was played exclusively by a group of wondering priests (“Komusou”), it is called the “Komusou shakuhachi” and regarded as the origin of the modern shakuhachi. Changes in acoustical design from the Sousouin shakuhachi to the Komusou shakuhachi are considered based on the input admittance calculated from the inner geometry. The blowing conditions of the Shousouin shakuhachi are estimated from the investigation carried out during 1948 to 1952. Some problematic points in cross-fingerings of the Shousouin shakuhachi are also discussed. The shakuhachi was originally introduced from China in the Tang dynasty around 750. Since this ancient shakuhachi has been preserved in the Shousouin of the Toudaiji temple, it is called the “Shousouin shakuhachi”. This shakuhachi, which has six tone holes to play a Chinese diatonic scale (e.g., A-B-Db-D-E-Gb-A, D-E-Gb-G-A-B-D), was adapted to play a Japanese pentatonic scale (D-E-G-A-B-D) by removing the second tone hole (Gb) around early 16th century. Moreover, the positions of five tone holes were modified to make effective use of the pitch bending (e.g., Eb) by drawing down players jaw and half-covering the tone hole(s) around the 17th century, and a scale pattern D-F-G-A-C-D was established. Since this shakuhachi (made from the root end of bamboo) was played exclusively by a group of wondering priests (“Komusou”), it is called the “Komusou shakuhachi” and regarded as the origin of the modern shakuhachi. Changes in acoustical design from the Sousouin shakuhachi to the Komusou shakuhachi are considere...

On the acoustical design of the ears of flue organ pipes

Application of the ears to the flue organ pipe is one of the important voicing techniques. Ears are the projections on both sides of the pipe mouth. Organ builders say the ears make not only the sound lower and darker, but also the buildup of tone smoother and quicker. The aim of this research is to confirm their recognitions and make the causes clear. For that purpose, we made acoustical and flow measurements (measurement of the velocity profiles at the mouth) with model pipes. As a result, we could confirm the recognition of the organ builders. In addition, our experiments indicate a slight increase in the blowing pressure in the foot and an increase in the inharmonicity of the pipe eigenmodes. The ear reduces the maximum jet velocity but keeps the characteristic profiles. In some cases, the profiles move as a whole more inside of the pipe. Recent acoustic measurements (eigenmodes of the pipe resonator and of the mouth tone, attack transient and stationary spectrum) on real organ pipes with ears of diff...