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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).
Road and dynamometer tests of an air silencer on experimental cars (20-EX, 22-EX).

Identifier  ExFiles\Box 13\4\  04-page066
Date  10th November 1932 guessed
  
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This air silencer appeared very satisfactory on the dynamometer, and so we again tested the car on the road with the result that the 57 - 63 m.p.h. roar was as good as cured, and from 63 m.p.h. upwards there was nothing to complain about. There were still slight evidences of roar between 40 and 50 m.p.h. and 33 to 38 m.p.h. on top gear, but as they appeared to be mingled with exhaust booms and engine periods (20-EX by the way is a very good car for showing up all noises), it was very difficult to say definitely which noise could be attributed to the carburetter, and which noises we could lay at the doors of the exhaust system, engine mounting, etc.

Hs.{Lord Ernest Hives - Chair} and Rm.{William Robotham - Chief Engineer} tried the car with this silencer fitted, with a standard silencer fitted, and with no silencer fitted at all, and agreed that we had obtained a fair degree of silence - say 70%.

Our next test was to try our silencer on 22-EX. First of all we tried the car without any kind of air silencer fitted, and found that the carb. roar was only 50% as bad as 20-EX. Our silencer was then fitted, and although it made a decided improvement it did not damp out the roar as well as it did on 20-EX.

We then tried varying the size of the tuning chamber (in case the characteristics of the two cars were not the same) and using two chambers - by-passing from one to the other, and finally came to the conclusion that we could not improve upon the size of tuning chamber as fitted to 20-EX, and that we had to turn our attention to a larger size of air intake with some form of baffling. We experimented with a large telescopic drum shaped air intake and obtained slight improvements, but on account of it fouling the bonnet, we decided to try an air silencer running along the top of the induction pipe. We are now waiting for this silencer to be made.

Hs{Lord Ernest Hives - Chair}/G.H. Whyman.
  
  


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