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).
Describing an instrument for measuring and comparing noise levels in car bodies.
| Identifier | ExFiles\Box 138\1\ scan0088 | |
| Date | 3rd May 1934 | |
| To Ev.{Ivan Evernden - coachwork} c. to Wor.{Arthur Wormald - General Works Manager} c. to Sg.{Arthur F. Sidgreaves - MD} X634 Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}6/KW.3.5.34. Measurement of Noises in Bodies. We give below the description of an instrument which might be useful in determining the relative silence of various types of body and assist in the detection of small differences due to modifications. We appreciate that measuring noise is something like measuring riding comfort, the difficulty being to convert what the instrument measures into the passengers' reaction, but it should be at least worth while trying out this device. If it is any good we have a number of applications in connection with engine mounting where it would be useful at Derby. "The portable acoustic meter of the Standard Telephone & 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 its masking effect. A chart can be used to convert the meter readings into equivalent sensation levels at 800 frequencies per sec." Possibly you will have an opportunity of trying this instrument in London and could let us know if it shows any possibilities. Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer} | ||