Cab noise can affect hearing
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INVESTIGATIONS had shown that in some vehicles the noise level could be high enough to cause permanent damage to hearing. This was said by Mr. T. Priede in a paper entitled "Noise and vibration problems in commercial vehicles" which he presented to the Institute of Road Transport Engineers last week. But, he said, the driver was unlikely to be subjected to the maximum level of noise for long enough periods except when driving on a motorway, and there would be periods when driving at lower speeds when the hearing loss could be recovered.
Mr. Priede dealt with all aspects of noise and vibration produced in a commercial vehicle, including the sources of the various types and methods of reducing the nuisance. Noise inside the cab in the lowfrequency range was caused by structureborne engine vibrations, he said, whilst the high-frequency range was caused by engine airborne noise. The predominant sources of noise on the outside were engine exhaust and inlet in the low-frequency range, but in the high-frequency range it was again airborne engine noise.
Exhaust and inlet noise could be dealt with by more effective silencers, but the task of controlling the airborne noise of a high-speed high-performance diesel was formidable. Various methods were possible, including the employment of sound-insulation techniques, controlling combustion and by a change in engine-structure design. Reductions of noise around 10 decibels were said to be readily obtainable.
Noise legislation defined the maximum level permitted at a certain distance, and a tentative figure of 85 decibels was being recommended. No recommendations were made to define the limits of noise in the cab, and Mr. Priede said that the ISO Noise Rating Criteria N.R.85 should be accepted as this was technically possible and was achieved in some modern vehicles.