Theory and design of high order sound field microphones using spherical microphone array

2002 ◽  
Author(s):  
Thushara D. Abhayapala ◽  
Darren B. Ward
Keyword(s):  
Microphone Array ◽  
Sound Field ◽  
High Order

scholarly journals Low Frequency Sound Field Reproduction within a Cylindrical Cavity Using Higher Order Ambisonics

2018 ◽  
Vol 36 (4) ◽  
pp. 649-655
Author(s):  
Yan Wang ◽  
Kean Chen ◽  
Jian Xu
Keyword(s):  
Green Function ◽  
Spherical Harmonics ◽  
Cylindrical Cavity ◽  
Microphone Array ◽  
Low Frequency ◽  
Sound Field ◽  
High Order ◽  
Acoustic Modes ◽  
The Green Function ◽  
Order Components

Sound field reproduction of the aircraft and submarine within a cabin mock-up using a loudspeaker array is of great importance to the active noise control technology.The conventional method is to calculate the driving functions of the secondary sources by solving an acoustic inverse problem in a least square sense, which requires a large number of microphones and only the sound field near the microphone array can be reproduced accurately.In order to overcome these drawbacks, higher order ambisonics (HOA) method which is widely used in spatial sound field synthesis for a large room is introduced to reproduce a low frequency sound field within a cylindrical cavity.Due to the different sound propagation characteristics within the cavity compared with a free field and a diffuse field, the Green function spectrum in spherical harmonics domain which is modeled as a superposition of the acoustic modes and the reproduction formulas are deduced.Reproduction characteristics are investigated by numerical simulations.Results show that for a small, the Green function spectrum in spherical harmonics domain is mainly concentrated on low orders and contributed by the low order acoustic modes, with the increase of, high order components of the Green function arise and the contributions of high order acoustic modes increase.In the reproduction process, the high order components of the pressure spectrum over the sphere in harmonics domain will be greatly amplified by the reproduction filter.Finally, HOA method is compared with the acoustic inversion method in terms of the microphone array system, the impact factors on the reproductions and the reproduction accuracy, and validated through experiments.Results show that HOA can better reproduce the entire sound field within the cylindrical cavity and the reproduction accuracy is improved.

scholarly journals Parametric spatial post-filtering utilising high-order circular harmonics with applications to underwater sound-field visualisation

2021 ◽  
Vol 149 (6) ◽  
pp. 4463-4476
Author(s):  
Vasileios Bountourakis ◽  
Leo McCormack ◽  
Mathias Winberg ◽  
Ville Pulkki
Keyword(s):  
Sound Field ◽  
High Order ◽  
Underwater Sound

Sound field interpolation in the spatial domain with a rigid spherical microphone array

2016 ◽  
Vol 140 (4) ◽  
pp. 2966-2966
Author(s):  
Cesar D. Salvador ◽  
Shuichi Sakamoto ◽  
Jorge Trevino ◽  
Yôiti Suzuki
Keyword(s):  
Microphone Array ◽  
Sound Field ◽  
Spatial Domain

Synthetic Sound Source Generation for Acoustical Measurements in Turbomachines

2013 ◽  
Author(s):  
Michael Bartelt ◽  
Juan D. Laguna ◽  
Joerg R. Seume
Keyword(s):  
Wind Tunnel ◽  
Sound Source ◽  
Sound Propagation ◽  
Microphone Array ◽  
Sound Field ◽  
Acoustic Mode ◽  
Acoustic Excitation ◽  
Noise Emission ◽  
Noise Sources ◽  
Sound Fields

One of the greatest challenges in modern aircraft propulsion design is the reduction of the engine noise emission in order to develop quieter aircrafts. In the course of a current research project, the sound transport in low pressure turbines is investigated. For the corresponding experimental measurements, a specific acoustic excitation system is developed which can be implemented into the inlet of a turbine test rig and into an aeroacoustic wind tunnel. This allows for an acoustic mode generation and a synthesis of various sound source patterns to simulate typical turbomachinery noise sources such as rotor-stator interaction, etc. The paper presents the acoustical and technical design methodology in detail and addresses the experimental options of the system. Particular attention is paid to the design and the numerical optimization of the acoustic excitation units. To validate the sound generator during operation, measurements are performed in an aeroacoustic wind tunnel. For this purpose, an in-duct microphone array with a specific beamforming algorithm for hard-walled ducts is developed and applied to identify the source locations. The synthetically excited sound fields and the propagating acoustic modes are measured and analyzed by means of modal decomposition techniques. The measurement principles and the results are discussed in detail and it is shown that the intended sound source is produced and the intended sound field is excited. This paper shall contribute to help guide the development of excitation systems for aeroacoustic experiments to better understanding the physics of sound propagation within turbomachines.

Investigation of Pantograph Effect on High-Speed Train Noise

2012 ◽  
Vol 233 ◽  
pp. 239-242
Author(s):  
Xiao Feng Zhang ◽  
You Gang Xiao ◽  
He Lian Deng ◽  
Jian Feng Huang
Keyword(s):  
High Speed ◽  
Microphone Array ◽  
Broad Band ◽  
Side Wall ◽  
Sound Field ◽  
Noise Spectrum ◽  
Low Noise ◽  
Sound Insulation ◽  
Vehicle Noise ◽  
Sealing Performance

Using microphone and removable planar microphone array, the exterior and interior vehicle noise near pantograph were investigated when the train ran at 250-350km/h, the noise spectrum characters of these areas were obtained. The results show that at the pantograph seat and in the vehicle below pantograph, the noise spectrum show a broad band distribution, and the noise energy is mainly concentrated within the range of 100Hz-2kHz. Interior vehicle noise below pantograph is a non-uniform reverberant sound field, the regions with larger sound pressure level (SPL) are distributed near the roof, the floor, the side wall below the luggage. For reducing interior vehicle noise below pantograph, such measures as using low noise pantograph, adding sound insulation pad, filling sound absorption materials and improving sealing performance should be taken, and these measures should be effective at 100Hz-2kHz.

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