ASA Lay Language Papers
161st Acoustical Society of America Meeting

Spectral filtering characteristics of a Motorcycle Helmet

Dr John Kennedy* -
Dr Nigel J Holt**
Dr Michael Carley*
Dr Ian Walker*

* University of Bath, UK
** Bath Spa University, UK.

Paper 5aNS14 12.05, Friday 27th May

Intuitively it is clear that wearing a motorcycle helmet will change the way in which people perceive sounds. There are both engineering and psychology aspects to understanding this process. It is the role of engineering to take the motorcycle helmet and carefully measure how sound is transmitted from the surface through the various components of the helmet. This is done by measuring how much sound energy, here referred to as intensity, passes through the structures of the helmet at each frequency. In engineering this is described as an insertion loss measure. Once the sound has passed through the helmet, understanding the motorcyclist’s perception of the sound is the role of the psychologist. It is for this reason that the Bath Motorcycle Research Initiative was formed which brings together researchers from the fields of aerodynamics, acoustics and cognitive psychology.

We know from previous research that motorcycle helmets reduce the intensity of sounds above 500Hz, a feature which we also found. However, our research showed that sounds below 500Hz were actually increased in intensity by the motorcycle helmet. From an engineering perspective this is an interesting result, but this does not allow us to understand how the rider will react to this change.

How people perceive the loudness of a sound depends on its intensity but also its frequency. The ear is most sensitive to sounds in the range of human speech, sounds outside this range need to be more intense for people to judge them as being equally loud. Equiloudness judgements of this kind have a long history in psychological research. In this type of measurement sounds of different frequencies are presented and listeners adjust the volume of one until both appear equally loud. In our task equiloudness measures made with and without a motorcycle helmet were compared and found to be strongly influenced by the helmet.

When these measures are combined with the insertion loss measurements these data help us better understand how riders perceive their environment while wearing a motorcycle helmet. Motorcycling is a complex task requiring an awareness of the riding environment. Sounds provide important feedback to enable the rider to respond appropriately to their surroundings. Our research is part of a wider project with the goal of protecting rider hearing health while insuring their ability to hear important sounds such as sirens, warning signals.

Contacts at the ASA, Sunday 22nd May to Wednesday 25th May – Dr John Kennedy and Dr Michael Carley (Affiliation – University of Bath, England)

Contact at the ASA Thursday 26th and Friday 28th – Dr Nigel Holt  (Affiliation – Bath Spa University, England)