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SOURCES AND LEVELS OF NOISE UNDER MOTORCYCLISTS' HELMETS

2024; Multidisciplinary Digital Publishing Institute; Linguagem: Inglês

10.25144/20217

2624-599X

MC LOWER, DW HURST, AR CLAUGHTON, Alison Thomas,

Noise Effects and Management

Noise levels at the ear under a motorcyclist's helmet increase rapidly as speed increases.At high speeds above about 60 or 70 kilometres per hour (35 -45 mph) the aerodynamic noise caused by the air ow around the motorcycle and rider exceeds the noise generated by the motorcycle itself.Noise exposures for many working riders such as police motorcyclists are lilter to atceed the First and Second Action Levels speci ed in the Noise At Work Regulations 1989 [I].An interim solution.adopted by some police forces.is to provide earplugs for motorcyclists.This is far from ideal.In the longer term it is desirable to reduce noise levels at the car by improving the aerodynamic and acoustic design of motorcycles and helmets.This paper brie y reports noise measurements in a wind tunnel and on the road to quantify noise levels and identify noise sources and paths. WIND TUNNEL MEASUREMENT SNoise levels and spectra were measured using calibrated miniature microphones (Knowles Electronics BT [759) at the ears of a motorcycle rider, a police driving instructor. in the 2.l m x 1.7 m (7 ft x 5 ft) Subsonic Wind Tunnel at the University of Southampton.Preliminary measurements showed the background noise levels in the tunnel to be suf ciently low not to affect the tests.TVvo motorcycles were used, a BMW K 100 and a BMW K 1100 LT.In each case measurements were made with several helmets.up to 27 samples of 13 di erent types or prototypes.Each helmet was allocated a number for identi cation.Airspeeds were 22. 27 and 32 m/s (approximately 50.60 and 70 mph) measured in the undisturbed ow upstream.Helmets were tested as supplied and with various treatments or modi cations in an attempt to identify where and how the noise was generated.to identify transmission paths of the noise from the source to the ear.and to reduce the noise at the car.Measurements on the K 100 motorcycle were made without a windscreen and with three screens of different heights.Measurements on the K 1100 LT were made with its electrically-adjustabl e windscreen at various heights.The various modi cations to helmes included: 0 ning draught excluder to seal the top edge or all around the visor.0 using insulating tape to seal the visor to the helmet and fair the visor into the helmet.O placing strips of draught excluder across the top of the helmet to modify the air ow, O changing the shape of the helmet with plastic or card attachmens at the front or back.I isolating the visor from the shell by replacing hinges with foam spacer and tape, 0 attaching an extra visor in front of the normal visor to keep the air ow off the normal visor.O sealing the gap around the riders neck.and.O with the help of a manu cturer.modifying the internal materials in contact with the helmet shell.close to the ears.at the forehead and around the chin bar.Time did not permit all modi cations to be tried with all helmets.All measurements reported here were made with closed visorsr Air ow and nrrbulence were mapped at the rider s position using a pitot tube and a hot-wire anemometer.Flow visualization techniques included smoke and wool tufts.