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).
Analysis of car body resonance, vibrations, and sound frequencies.
| Identifier | ExFiles\Box 41\3\ Scan239 | |
| Date | 12th December 1922 guessed | |
| contd:- -2- even then we think there would be no tangible results since the exhaust note would probably be in a higher scale. The main wave can have a frequency of from about 7 vibrations per second upwards (from 3 m.p.h. on top gear) but the secondary wave being audible is of much higher frequency. It is not necessary for the disturbing vibrations to be exactly of the same frequency as the disturbed medium, but the resonance of the latter increases as they more nearly synchronise and then tails off. A body consisting of a rigid box will always have a resonant period but it is believed that, provided it has a frequency sufficiently high that its note can be sung with effect, it will not be objectionable. The lowest musical note is about 40 per second, the lowest audible note about 16 per sec. but the lowest average vocal note is above these. Whilst we can possibly do a lot to relieve the car of chassis vibrations, yet we agree with you that all the while it has an engine, and runs on the road, it will have these and other vibrations to a greater or lesser degree. We feel therefore that the body will have to be so constructed either that due to its plastic nature it cannot become resonant, or else be made so that its note is higher, and not unpleasant. The American leather roof constructed over sticks covered with rabbit-netting and felt is an example of the former, and a roof stiffened with steel edge plates along its sticks is the latter (as for example the Maythorn saloon). In the older days of luggage being carried on the roof booming did not seem to be so pronounced due to the roof having to be stiffened outside contd | ||