Spectral filtering characteristics of a motorcycle helmet

Noise transmission characteristics of a motorcycle helmet have been analysed using a combination of insertion loss measurements and loudness matching in a behavioural study. Results demonstrate the action of the motorcycle helmet as a spectral filter. The insertion loss measurements confirm previously published data showing attenuation in the frequency range above 500Hz. A further feature, the significance of which is addressed and highlighted here for the first time, is an amplification of noise below 500Hz. In short, the helmet acts as a frequency dependent filter on the input to the human auditory system. Data from the matching task were used to generate equiloudness curves which show the effect of the helmet on riders' perceptions of loudness. The generated curves were compared to the international standards (ISO226). The character of the equal loudness curves was strongly influenced by the helmet. This difference is discussed in the framework of the filtering characteristics of the helmet.