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).
Sources of vibration and booming sounds in a limousine trials car.
| Identifier | ExFiles\Box 41\3\ Scan238 | |
| Date | 12th December 1922 | |
| X.3730. To Hs.{Lord Ernest Hives - Chair} from Da{Bernard Day - Chassis Design}/EV.{Ivan Evernden - coachwork} c. to Da.{Bernard Day - Chassis Design} & EP.{G. Eric Platford - Chief Quality Engineer} Da{Bernard Day - Chassis Design}/EV{Ivan Evernden - coachwork}3/M12.12.22. RE. LIMOUSINE TRIALS CAR X.3730. Thank you for your memo. Hs{Lord Ernest Hives - Chair}2/LG9.12.22. Our Da{Bernard Day - Chassis Design}/EV{Ivan Evernden - coachwork}2/M5.12.22., was merely intended as a suggestion, though unfortunately somewhat badly worded. We would have certainly liked to have spent longer with the car before expressing an opinion. Of the various sources of energy which may cause a body to boom the engine is only one, besides also the axle gears there are the axle vibrations due to road bumps causing the body to boom even when the car is coasting down a decline. The vibrational energy from the engine can possibly reach the body in two paths, i.e., by direct metallic connection or by means of sound waves. To reduce the effect of the former various methods of body and engine insulation have been used, but to counteract the effect of sound waves very little can be done, and one does feel that these engine vibrations coming through the air could cause the body to boom similarly to the engine torque, of which they are the same frequency. The actual tone of the exhaust note can be looked upon as a secondary wave travelling on the back of the main wave. The frequency of the main wave is proportional to the engine speed but to alter the note of the exhaust is only to change the nature of the secondary wave, and not the one which is the root of the trouble. One can however imagine a case in which the resonant note of the exhaust system was a function of the body note but contd:- | ||