Motorcycle helmets and the frequency dependence of temporary hearing threshold shift

Temporary hearing threshold shifts (THTSs) as a result of exposure to noise vary as a function of the noise's spectral content. However, to date THTS has been measured and predicted in a way that does not take account of frequency variation-most notably in standards such as British Standard 5330. We therefore carried out pure tone audiometry on participants before and after exposure to white noise in order to quantify the frequency dependence of the THTS. Moreover, as this research group has previously shown that motorcycle helmets act as spectral filters, attenuating noise in the region above 500Hz and amplifying noise in the regions below 500 Hz, this was done both with and without a motorcycle helmet. As our previous findings would suggest, the pattern of threshold shift is a function of the filter characteristics of the helmet, including an increased sensitivity at higher frequencies. There was also greater than expected reduction in sensitivity at frequencies where the helmet amplifies incident noise. The results indicate an acoustic effect of helmets which has not previously been reported.