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).
Letter from the Anglo-Persian Oil Company discussing engine noise measurement techniques using a Strobophonometer.
| Identifier | ExFiles\Box 165\4\ img157 | |
| Date | 1st July 1932 | |
| C.S.31. x4691 Anglo-Persian Oil Company, Limited. BP Research Station. Telephone: Sunbury 390. Your Reference HS{Lord Ernest Hives - Chair}/Ud.3/MJ Our Reference RS{Sir Henry Royce's Secretary}/DF P.O. Box 1, Chertsey Road, Sunbury-on-Thames. 1st July, 1932 £200 Dr. L. R.{Sir Henry Royce} Underwood, Rolls-Royce, Limited, Experimental Department, D E R B Y. Dear Underwood, I am enclosing a copy of this month's I.P.T. Journal in which is a fairly full description of the Strobophonometer. It should be quite satisfactory for the applications you mention, although a little experimental work might be necessary to determine exactly how to get the true comparison of noise between the various cylinders especially if these are at widely different distances from the microphone. If the microphone is clamped, say, near the centre of an engine of the radial type, then there ought to be no difficulty in comparing values of noise to within a few per cent. Any such comparison is, of course, only approximate with the most elaborate apparatus, since echo effects may give some cylinders undue prominence due to the disposition of engine surroundings, building walls etc. It is surprising to what extent echo can alter noise ratios. In the case of a six in line engine, or a twelve Vee, the microphone could be placed above the lines of cylinders at some distance away, so that it was at substantially the same distance from each head. Alternatively, it would be possible to use as many microphones as there are cylinders, and to fit a multi-way switch to change from one to another. The objection to this method is | ||