Ear Muff Performance in Impulsive Noise as a Function of Angle of Incidence
The European directives regarding noise exposure limits require knowledge of the attenuation of impulse noise obtained from hearing protectors. To clarify this matter a European joint project was performed. Our part of the project was to investigate the influence of sound incident angle on the attenuation of ear muffs, especially for impulse noises. The impulse response in the ear canal of 16 subjects was measured in an anechoic chamber at the incidence angles of 0° to +90° in steps of 15° and from 180°. This was made without ear muff and with three different types of ear muffs, Bilsom Viking 2421. Peltor H7A and Willson 358A, respectively. These impulse responses were then convolved with three types of impulses. Mean and standard deviation of attenuation values for the peak of the impulses were calculated (linear assumptions!). In most cases the lowest attenuation of the peak was found at 180°. Attempts were made to predict these peak attenuation values from SNR (Single Number Rating), PNR (Predicted Noise level Reduction) and octave-band attenuation values proposed in ISO DIS 4869-2. The latter gave mostly good (error < 2 dB) or in some cases fairly good (error < 4 dB) predictions, the PNR-values gave fairly good predictions except for the impulse with the main energy in the 4 kHz octave. The SNR-values gave bad predictions except for the impulse with the main energy around 1 kHz. This investigation supports the idea to predict the attenuation for various types of impulse noises from attenuation data proposed in the ISO DIS 4869-2 standard, if the frequency region containing most energy is known and considered.
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Document Type: Research Article
Publication date: 01 September 1996
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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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