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Conference_programme: 12.3 - Active Noise and Vibration Control

Lecture: Adjustability of acoustic properties of surfaces at low frequencies by an array of active resonators

Author(s): Kanev Nikolay

Surfaces with variable acoustic properties are useful for many applications. For example, in multipurpose concert halls adjustable acoustic treatment is often installed to accommodate different types of performances. There are many solutions changing acoustics of the room by means of removable panels or draperies. These solutions provide sufficient flexibility in room acoustics at medium and high frequencies, whereas variations at low frequencies are not significant. In this paper a concept of surfaces with actively controlled acoustic properties is presented. An array of secondary sound sources is placed near the flat surface with arbitrary acoustic properties or mounted onto the surface. Each secondary source is an active resonator, which is an electromechanical device consisting of a loudspeaker connected with a microphone by a feedback. The acoustic impedance of the loudspeaker is actively controlled in wide frequency band. This device was designed and experimentally investigated some years ago. Now the array of the active resonators is considered. It is shown that the array may absorb, reflect or diffuse incident sound waves in dependence on adjustment of the active resonators. Proposed approach is very effective at low frequencies when a distance between the active resonators is smaller a half wavelength. In some cases efficiency maybe good enough if the distance is not greater the wavelength. Two types of sound field are considered. Absorption and scattering coefficients for a plane wave incident on the surface with actively controlled properties are found. Absorption of the diffuse sound field by the surface is analyzed as well.

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Corresponding author

Name: Dr Nikolay Kanev

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Country: Russian Federation