Acoustic Study on Motorcycle Helmets with Application of Novel Porous Material

A critically high noise level inside protective helmet is a prevalent concern for motorcyclists. Especially at highway speeds where the noise level, regardless of helmet type can exceed 100 dB(A) and approaches threshold of discomfort, often resulting in temporary hearing loss. Despite of large share of persons exposed to such noise disturbance around the world, the in helmet noise levels have not significantly decreased over the last decades. Only few scientific publications can be found to systematically address this issue. Furthermore, in respect of driving safety even moderate noise levels are reported to impair reaction times and reduce attention of motorcyclists. At higher speeds the dominant helmet noise source is linked to aerodynamic turbulence around the helmet shell. The loudness and spectral contents mainly depend on the driving speed, windscreen configuration, riding position and helmet geometry. In this paper a series of on-road tests and laboratory experiments with three main types of helmets (“full face”, “flip up” and “open face” type) have been performed with the focus on in-helmet acoustics. Noise spectra at the location of rider's ears are measured, the results are analyzed and the noise source mechanisms are studied. A novel acoustic material, consisting of reticulated natural leather foam is presented for helmet noise control applications. It is demonstrated that a remarkable helmet noise level reduction can be achieved in a wide frequency range by the material into the critical interior regions of motorcycle helmets.