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).
Vehicle body resonance, sound absorption materials, and potential experiments to reduce engine noise.
| Identifier | ExFiles\Box 173\1\ img286 | |
| Date | 12th February 1934 guessed | |
| II Coachwork Accoustics There was an interesting discussion on body resonance at the S.A.E. meeting. They have been doing a vast amount of research on this. From our point of view, it would seem imperative to have a car and investigator permanently allotted to the subject. For instance, they say they can make a body now which is so good acoustically that one can run from tarmac onto sets without getting an internal boom! They stress the scuttle armature, roof particularly the curved edges thereof, back and floor as being the most profitable places of attack for low frequency booms. I shall get more information on the sound absorption materials used, but the "Limpet" asbestos treatment would seem to be a good one to start on. They say this is O.K. for sheet metal but not for floor boards, which they treat much as we have done. The test bodies which are so bad should be ideal pieces of apparatus to start on. Again there seems to be common agreement that a metal dash is a sounding board for engine noises and high frequency vibrations generally. I suggest as an experiment handing a cast dash to the pattern makers and asking them to reproduce it in five ply, or alternatively make a double skin of the flat surfaces, then fit to a car. Also rubbering the rear engine mounting should reduce noises getting to the frame and hence to the body. A quick test on tappet covers, cast one in lead to see what that does. Plymouth ran into trouble with tappet noise by changing the material of their valve and nothing else. General view is that noise will be one of the greatest difficulties with an all aluminum engine. They have accepted that you must use a noise measuring apparatus for small differences. I shall go to the proving ground to see just what set-up they have. The enclosed paper gives some useful information for any one starting a series of tests. | ||