Simple Model for Predicting the Insertion Loss of a Straight Tube Silencer
The simplest model for predicting the insertion loss of straight ventilation silencers is Piening's model. However, it can be applied only below the cut-off frequency, which is, for typical silencers, between 160 and 2000 Hz. Above the cut-off frequency, Piening's model overestimates strongly the insertion loss. The purpose of this study was to introduce a simple high-frequency extension to Piening's model. The model was based on the presumption that the wall of the silencer is highly absorbing so that plane wave is the dominating waveform in the silencer at high frequencies. The cross-sectional area of the duct was divided into the absorption and the transmission band. The absorption band locates close to the absorbing walls and the transmission band in the middle of the silencer. The thickness of the absorption band is approximately a half wavelength. At low frequencies, the absorption band covers the whole cross-section of the silencer. Above the limit frequency, the thickness of absorption band decreases with increasing frequency so that at high frequencies only small part of cross-section belongs to absorption band. This explains why the insertion loss of silencers decreases strongly above the cut-off frequency. Two specimens were measured in the laboratory according to ISO 7235. The predicted insertion loss was close to the measured insertion loss except below the limit frequency where the model underestimated the insertion loss by 10 dB for both specimens. The existence of absorption and transmission bands could be proved by radial sound level measurements inside the silencer.
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Document Type: Research Article
Publication date: September 1, 2004
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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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