From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
New portable noise measuring apparatus from the Standard Telephones & Cables Ltd.
| Identifier | ExFiles\Box 138\1\ scan0089 | |
| Date | 1st March 1934 | |
| [Handwritten] As/Rm{William Robotham - Chief Engineer} doin this while to measure decibels of various articles as directed you By Please return [Typed] I.A.E. RESEARCH AND STANDARDISATION COMMITTEE Research Department, 5, Bolton Road, Chiswick, W.4. No. 7071. Class 27. March, 1934. New Portable Noise Measuring Apparatus ------------------------------------- Engineer, March 2, 1934, p. 234. ------------------------------------- The portable acoustic meter of the Standard Telephones & Cables Ltd., is designed to measure noise in a simple manner. It operates over a wide range of noise intensities and indicates the results directly in decibels. The instrument makes use of the 'offset' receiver method of measurement in which the observer listens simultaneously to the noise under test and to a standard reference noise in the headphone receiver. The observer has only to determine the point at which the reference tone is just audible, without having to estimate equal intensities. Where, however, single high-frequency components occur a normal ear cap is supplied to replace the 'offset' cap, the measurements then being made by estimating equal intensities of noise. In using the instrument a clockwork motor is wound up, a motor brake released and a rheostat adjusted, the operating current being supplied from a single low-voltage battery. The alternator dial and switches are adjusted until the noise under test just fails to mask the reference tone heard in the receiver. The reading obtained is a measure of the intensity of the observed noise in terms of the intensity of its masking effect. A chart can be used to convert the meter readings into equivalent sensation levels at 800 frequencies per sec. H.L. | ||