Characteristics of Typewriter Noise

Abstract

Measurement of noises of short-time duration, such as typewriter noise, is not satisfactory when carried out using conventional sound level meters. Availability of an Impact Noise Analyzer allows measurement of peak levels and decay-time constants of typewriter noise. The measurement and evaluation of typewriter noise using this instrumentation is reported in this paper. Peak sound power levels due to type impact were found to be 90±5 db, with an average decay-time constant of 2–3 msec. Investigation of typewriter noises using this instrument also reveals that the decay-time constant is as important a parameter characterizing a short-time duration noise as is its peak level. Decay-time constants of noises due to different typewriter operations were found to vary from 2 msec to over 300 msec. Octave and third-octave band analyses of typing noise were also carried out using the Impact Noise Analyzer. The most important frequency bands of noise due to type impact were found to be those above 1200 cps. Relative energy of the noise in octave bands indicates that type impact noise, and the noise generated in the desk supporting the typewriter, are the most important sources of noise in typing. (This work was carried on in the General Research Laboratory of the Underwood Corporation, Hartford, Connecticut.)