Noise and Vibration Control in Engineering

under the worst conditions of ambient noise.A recent investigation was carried out by the Coal Board to determine the suitability of various devices to signal the impending start of coal face machinery.It was found that bells, hooters and sirens were all about equally effective in being heard above coal face noise.In this case the electro-acoustic conversion efficiency was not considered.The tone transducer has been tested in a similar way by comparing it with a telephone bell in a noisy location.This was a room housing punched-card accounting machines producing a noise level of about 90 phons.The transducer was operated over a range of frequencies and power inputs and it was found that even when operating on lower power than the bell, the transducer gave a sound output that was more easily distinguishable than that of the bell against the background noise. Noise and Vibration Control in Engineering