Dr Michael Carley* - m.j.carley@bath.ac.uk
Dr John Kennedy*
Dr Nigel J Holt**
Dr Ian Walker*
* University of Bath, UK
** Bath Spa University, UK
Popular version of paper 5aNS12
Presented 11:35, Friday, May 27, 2011
161st ASA Meeting, Seattle, Wash.
Motorcyclists ride for all sorts of reasons: the freedom of the open road, the excitement, the convenience and the reduced impact on the environment of their transport choice. Noise is important to biking and many riders love the rush they get from a throbbing exhaust or a screaming engine. The thrill has a price, however: noise can seriously damage hearing and stop you enjoying hard biker rock - quite a price to pay. In our work, we have studied the causes of this noise and, surprisingly, it's not the engine or the exhaust that are important, but the helmet. We have also looked at the effects of this noise on the road, in the laboratory and in our wind-tunnel.
It may come as a surprise, but noise in motorcycling is largely caused by air flowing over the rider's helmet, not the engine. This noise, which can only be heard by the rider, is not altered by the throttle or the size of the pipe in the way that exhaust noise is. It exceeds safe limits even at legal speeds and in many countries it would be illegal to expose employees to such high noise levels. Indeed, the first studies of this problem were carried out by police forces who were finding that their riders' hearing was seriously damaged by their long hours on the open road - crime fighting is costly, it seems, not just to your wallet, but also to your health. One solution to the problem of noise is to wear ear plugs. These reduce noise levels and so help protect riders' health. But even with earplugs there is still a lot of noise being transmitted into the rider's ears, mostly through vibrations in the skull. Also, earplugs are a blunt tool, and stop riders hearing important sounds like ambulance sirens just as much as they stop riders hearing wind noise. We have, therefore, been exploring exactly what causes the noise a rider hears. Once we fully understand where the noise comes from, we can manipulate it however we wish.
We started by measuring the noise on the road, with tiny microphones in a rider's ears, and then moved into the wind tunnel, to do the same with a model head. While the helmet is the main source of noise in both wind-tunnel and on-road tests, each environment also contains other noise sources. By applying rigorous analysis techniques to the recordings we were able to show that the helmet noise in each case was the same. This means that we now know how to take wind tunnel measurements and match them to what a rider hears on the road. The final element of the work is to measure the effect of the noise on a rider, and how this is affected by the helmet.
To achieve this we must go beyond tests in a wind tunnel and on individual riders and so we are now testing groups of listeners in our cognitive psychology lab. To date our research group has looked at the effects of motorcycle noise on hearing health, and perceptions of loudness, both presented here at the ASA. In addition to this we are conducting pilot studies investigating the influence of noise on rider attention and hazard perception - vital knowledge in ensuring rider safety.
Contacts at the ASA, Sunday 22nd to Friday 28th May - Dr Michael Carley and Dr John Kennedy (Affiliation, University of Bath, England)
Contact at the ASA Thursday 27th and Friday 28th May - Dr Nigel Holt (Affiliation, Bath Spa University, England)
Department of Mechanical Engineering
University of Bath
Bath
BA2 7AY