The Problem of Offset in Measurements Made Using Acoustic Pulse Reflectometry
Acoustic pulse reflectometry is a useful non-invasive technique for measuring the input impulse response, input impedance and internal dimensions of ducts. A sound pulse is injected into the duct under investigation and the resultant reflections are recorded. Suitable analysis of the reflections then yields the input impulse response, from which both the input impedance of the duct and its cross-sectional area as a function of distance can be calculated. However, an input impulse response measurement made using acoustic pulse reflectometry generally contains an offset. Unless this offset is removed, the application of a bore reconstruction algorithm results in a calculated duct profile which expands or contracts spuriously. In this paper, the offset introduced into reflectometry measurements is shown to consist of both constant and time-varying components. The origins of these DC and time-varying offsets are examined and methods of preventing or removing them are investigated. Finally, improved accuracy bore reconstructions, calculated from input impulse response measurements where any offset has been eliminated, are presented.
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Document Type: Research Article
Publication date: July 1, 2005
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- Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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