Journal of the Acoustical Society of Japan (E)
Online ISSN : 2185-3509
Print ISSN : 0388-2861
ISSN-L : 0388-2861
Volume 11, Issue 6
Displaying 1-6 of 6 articles from this issue
  • Shoji Makino, Shoji Shimada
    1990 Volume 11 Issue 6 Pages 309-316
    Published: 1990
    Released on J-STAGE: February 17, 2011
    JOURNAL FREE ACCESS
    This paper reviews echo control techniques for telecommunications, emphasizing the principles and applications of both circuit and acoustic echo cancellers. First, echo generating mechanisms and echo problems are described for circuit and acoustic echoes. Circuit echo is caused by impedance mismatching in a hybrid coil. Acoustic echo is caused by acoustic coupling between loudspeakers and microphones in a room. The echo problem is severe when the round-trip propagation delay is long. In this case, the echo must be removed. Next, the basic principle of the echo canceller, adaptive filter structure and adaptive algorithm are discussed. Emphasis is focused on the constructionand operation of an adaptive transversal filter using the NLMS (Normalized Least Mean Square) algorithm, which is the most popular for the echo canceller. Then, applications of circuit and acoustic echo cancellers are described. Circuit echo cancellers have been well studied and implemented in LSIs for many applications. Although acoustic echo cancellers have been introduced into audio teleconference systems, they still have some problems which must be solved. Therefore, they are now being studied intensely. Finally, this paper mentions the problems of echo cancellers and the direc tionof future work on them. The main targets for acoustic echo cancellers are improvingthe convergence speed, reducing the amount of hardware and bettering the double-talk control technique.
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  • Adaptive microphone-array system for noise reduction
    Akitoshi Kataoka, Yutaka Ichinose
    1990 Volume 11 Issue 6 Pages 317-325
    Published: 1990
    Released on J-STAGE: February 17, 2011
    JOURNAL FREE ACCESS
    This paper describes a microphone-array configuration for AMNOR (Adaptive Microphone-array system for NOise Reduction). AMNOR performance (S/N improvement) depends on the microphone-array configuration. Therefore, the chosen configuration is examined under three different sound field conditions by simulation experiment. The distance between two microphones is first described in detail to show that the optimum microphone distance is one-half the wavelength of the highest frequency in the broadbandnoise of interest. Based on these results, linear and circular-array configurations are next examined. These configurations can obtain similar results by the introduction of apparent microphone distance. The maximum value of this distance should also be one-half the wavelength of the highest frequency of the broadband noise.
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  • Nobuomi Tmai
    1990 Volume 11 Issue 6 Pages 327-333
    Published: 1990
    Released on J-STAGE: February 17, 2011
    JOURNAL FREE ACCESS
    The improvement in performance of the microphone using piezoelectric creamic which includes the FET circuit, is described in this research report. The most important point in the design of the microphone is how to improve the transduction efficiency. This paper analyzes a microphone as a system consisted of a number of subsystems. Suppression of the energy transmission loss between these subsystems is an important requirement in designing the microphone. This paper also solves this problem by dividing the electrode of the piezoelectric ceramic and connecting the divided electrodes in series. A large output is obtained by input of high voltage into the FET which has voltage drive characteristics. High performance and stability were obtained by this microphone together with the use of ceramic for the entire diaphragm system in the prototype microphone. The performance characteristics of this prototype microphone are Sensitivity:-35.8 dB/Pa 1 kHz, Electrostatic capacitance: 275 pF, Frequency response:±1.5 dB at 20 Hz to 12.5 kHz.
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  • Nobuomi Imai
    1990 Volume 11 Issue 6 Pages 335-341
    Published: 1990
    Released on J-STAGE: February 17, 2011
    JOURNAL FREE ACCESS
    A wide range ceramic microphone using a round flat type diaphragm is described in this research report. Use of the ceramic electrode diameter as the parameter is proposed for setting of the upper frequency limit. A concentric mode of vibration will appearin the vicinity of the secondary and tertiary resonance frequencies in the range above the primary resonance frequency of the diaphragm. Since the generated voltagewill be the highest at this center (inside the inflection point), the maximum power can be obtained by determining the electrode diameter according to the frequency. When high voltage obtained from this maximum power is supplied to the FET, a large output voltage can be obtained with the optimum signal-to-noise ratio. The performancecharacteristics which were realized by this prototype capsule of ∅23.77 are Sensitivity:-40.2 dB/Pa. 1 kHz; Electrostatic capacity: 118 pF, and Frequency response:±2.5dB at 20Hz to 20kHz.
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  • Hideo Suzuki, Masazou Anzai, Takahiko Ono, Frank Fossaert
    1990 Volume 11 Issue 6 Pages 343-349
    Published: 1990
    Released on J-STAGE: February 17, 2011
    JOURNAL FREE ACCESS
    In an active noise control or in sound reproduction, it is important to know self and mutual radiation impedances of sound sources. Since the total radiated power from sound sources is determined by self and mutual radiation resistances and velocities of the radiating surfaces, it is possible to determine the radiation resistances from the measurement of radiated power and velocities. Radiation resistances of two loudspeakersmeasured in a large meeting room are on the same order of a rigid piston in an infinite baffle, but show large irregularities due to complex radiation conditions. The mutual radiation resistance decreases significantly by increasing the distance between the loudspeakers.
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  • Katsumi Suzuki, Hiroaki Takinami
    1990 Volume 11 Issue 6 Pages 351-357
    Published: 1990
    Released on J-STAGE: February 17, 2011
    JOURNAL FREE ACCESS
    In recent years, condenser microphones which are polarized with an electret film (herein referred to as “electret microphones”) are increasingly used instead of condenser microphoneswhich need an external voltage source for polarizing (herein referred to as “condensermicrophones”) as acoustic measurement microphones, especially for sound level meters. This is because electret characteristics have been remarkably improved, due to great progress in electret source materials and manufacturing technology. In this paper, first we will present an outline of electret materials and some evaluation methods of electret characteristics. Then we will state the respective advantages of condenser microphones and electret microphones. And finally we will introduce two samples of electret microphones which were designed for sound level meters by Rion Co., Ltd.
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