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Tsuru H.,Nittobo Acoustic Engineering Co. | Iwatsu R.,Tokyo Denki University
International Journal of Adaptive Control and Signal Processing | Year: 2010

In the marine engineering field, a sound wave is often utilized to visualize objects. In such a sensing method, an accurate numerical prediction of sound propagation is an important issue for theoretical considerations. Recently, a finite difference method in time domain (FDTD) is often applied to wave propagation. However, an existing FDTD sometimes fails to match the accuracy to be required. In the present paper, strategies to improve conventional methods are presented: the application of the compact finite difference on staggered grid with adjusted coefficients and the usage of optimized multistep time integration. It is shown that through these tactics, a highly accurate simulation is attainable. Copyright © 2009 John Wiley & Sons, Ltd.

Williams E.G.,U.S. Navy | Takashima K.,Nittobo Acoustic Engineering Co.
Journal of the Acoustical Society of America | Year: 2010

A technique is described to image the vector intensity in the near field of a spherical array of microphones flush mounted in a rigid sphere. The spatially measured pressure is decomposed into Fourier harmonics in order to reconstruct the volumetric vector intensity outside the sphere. The theory for this reconstruction is developed in this paper. The resulting intensity images are very successful at locating and quantifying unknown exterior acoustic sources, ideal for application in noise control problems in interior spaces such as automobiles and airplanes. Arrays of varying numbers of microphones and radii are considered and compared and errors are computed for both theory and experiment. It is demonstrated that this is an ill-posed problem below a cutoff frequency depending on array design, requiring Tikhonov regularization below cutoff. There is no low frequency limit on operation, although the signal-to-noise ratio is the determining factor for high-spatial resolution at low frequencies. It is shown that the upper frequency limit is set by the number of microphones in the array and is independent of noise. The accuracy of the approach is assessed by considering the exact solution for the scattering of a point source by a rigid sphere. Several field experiments are presented to demonstrate the utility of the technique. In these experiments, the partial field decomposition technique is used and holograms of multiple exterior sources are separated and their individual volumetric intensity fields imaged. In this manner, the intensity fields of two uncorrelated tube sources in an anechoic chamber are isolated from one another and separated intensity maps are obtained from over a broad frequency range. In a practical application, the vector intensity field in the interior of an automobile cabin is mapped at the fundamental of the engine vibration using the rigid sphere positioned at the driver's head. The source regions contributing to the interior cabin noise are identified. © 2010 Acoustical Society of America.

Iwatsu R.,Tokyo Denki University | Tsuru H.,Nittobo Acoustic Engineering Co.
Theoretical and Applied Mechanics Japan | Year: 2012

We consider an application of a group of fourth order compact finite difference schemes on staggered mesh and third order symplectic integration methods to the linear wave equation. The objective is to improve resolution efficiency of the conventional method for acoustic problems. In the present study, we report the results of stability analysis and phase error analysis. Four methods are analyzed and compared for a benchmark test problem. It is shown by the analysis and by the benchmark problem, that one method among the four methods tested perform substantially better than the rest of the methods.

Hirosawa K.,Nittobo Acoustic Engineering Co.
40th International Congress and Exposition on Noise Control Engineering 2011, INTER-NOISE 2011 | Year: 2011

Many multi-layered structures or materials have been developed to expand its effective frequency ranges and to improve its acoustical performances. The multi-layered materials are also useful in vehicles, because those should be thin and light-weighted to achieve both low fuel consumption and interior quietness. The porous materials can be used for the sound absorption, but they are usually effective only in high frequency. In order to overcome poor acoustical performance in low frequency, the perforated panels can be combined with the porous materials. This study is focused on the absorption characteristic of the multi-layered structure included the perforated panel. The statistical absorption coefficient of the structure is estimated by the transfer matrix method which the finite area effect is considered as an application of the radiation impedance.

Nittobo Acoustic Engineering Co | Date: 2011-07-12

The open air layer-type vibration reduction structure is provided with at least one plate-like member of which the obverse surface faces toward the open space side; and a frame spaced at an interval from the reverse surface of the plate-like member, and an air layer is formed between the plate-like member and the frame. An air-permeable ventilation portion is formed at least one of the plate-like member and the frame, such that the average value of the flow resistance on the surface of at least one of the plate-like member and the frame, which forms an air layer, is in a range greater than 0 Ns/m^(3 )and equal to or less than 1,000 Ns/m^(3), The ventilation portion may be configured such that the sound pressure level generated within the air layer by applying an external force to the air layer is reduced by 3 dB or more.

Nittobo Acoustic Engineering Co. | Date: 2013-07-11

Provided is a noise identifying apparatus and noise identifying method, allowing automatic identification of whether or not a measured noise has been influenced by a non-object noise, using a simple system. Apparatus includes a sound detection unit, including plural microphones and/or particle velocity sensors; a sound source direction specifying unit, specifying an instantaneous direction of a sound source for each unit time, on the result of detection by the sound detection unit; a variation degree calculating unit, calculating a variation degree of the plural instantaneous directions specified by the sound source direction specifying unit for a prescribed period set longer than the unit time; and a non-object noise determining unit, determining the existence/absence of a non-object noise having influenced the measurement of an object noise taken as an object to be measured, coming from a noise source, on the variation degree calculated by the variation degree calculating unit.

Nittobo Acoustic Engineering Co. | Date: 2010-09-29

A sound source can be identified and measured for a long time period outdoors and indoors. A sound source identifying and measuring apparatus including a baffle provided with a frame and a weather-resistant screen for providing an aerial clearance is used for long-term indoor and outdoor measurement at a sound source measurement location to acquire sound source information in all the directions and associate the azimuth, elevation, sound pressure information and/or frequency characteristics or the like per elapsed time. A directional digital filter as well as identification parameters of a target sound source and untargeted sound source are used to identify the sound source more accurately for identification and measurement of the target sound source. Contribution of all of a plurality of sound sources to a sound pressure level is separated in terms of the coming direction for analysis. Thus, whether or not the sound source is a target sound is determined, and determination such as estimation of its sound source intensity and sound pressure level is made.

The acoustic performance of acoustic materials is readily studied for various values of the material parameters characteristic of acoustic materials. An acoustic performance calculation device is provided with an acoustic performance calculation device that calculates the acoustic performance of acoustic materials for each of a plurality of values in a pre-specified numerical range for each of a plurality of material parameters characteristic of acoustic materials based on a mathematical model for mathematically representing acoustic material, a contour map drawing device for drawing a contour map representing the calculated acoustic performance by contours where the two axes are the values of one material parameter and the frequency, and a plot drawing device for plotting the performance curves showing the relationship between the frequency and the acoustic performance for one value in the numerical range.

Provided are a sound generation system and a sound recording system, which are placed in a room to adjust sound. A columnar body is disposed around a sound source to adjust how much sound of a low-tone range, as well as of a middle- and high-tone range, is absorbed and diffused. Moreover, a columnar body is disposed around a recording device to adjust how much sound of a low-tone range, as well as of a middle- and high-tone range, is absorbed and diffused. The columnar bodies may be made of a combination of different diameters and/or lengths. The arrangement distances may be random. With the columnar body disposed at the most appropriate location, it is possible to adjust sound in a wide band.

Nittobo Acoustic Engineering Co. | Date: 2012-05-08

Measuring or testing machines and instruments and parts thereof, namely, sound level meters and acoustic meters, acoustic measuring systems, namely, apparatus for recording, transmission and reproduction of sound and visual sound images; electronic machines and parts thereof namely, electroacoustic sound transducers, apparatus and instruments for measuring, controlling, testing, regulating and checking sound and vibration, apparatus for vibration measurement, monitoring and diagnosis, namely, vibration meters, electro-technical vibration meters, sound and vibration analyzers, acoustic analyzers, electro-acoustic analyzers, structural dynamics analyzers, data acquisition amplifiers, conditioning amplifiers, hand-held vibration analyzers, noise dose meters, noise monitoring terminals, acoustic transducers, microphones, hydrophones, vibration transducers, accelerometers, calibration systems for monitoring and diagnosis of sound volume, quality and frequency and for monitoring and diagnosis of vibration; electrical apparatus and parts thereof for machine monitoring and diagnosis of sound volume, quality, frequency and vibration.

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