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).
Investigation into body and frame resonance, exploring sound transmission and potential causes of booming.
| Identifier | ExFiles\Box 12\6\ 06-page036 | |
| Date | 25th March 1931 guessed | |
| (3) (2) Then the body is lowered and rigidly mounted to the chassis without the subframe mounting. If the boom returned it would prove that direct transmission between the body and the frame had occurred. The resonant medium. The frame, column and dash to us are purely transmitting media and are in no way resonant with the vibrations they transmit. Hence being damped or weighted would not effect their action. We note that you have had jacks under the frame, but we believe that to destroy the torsional flexibility of the frame it would be necessary to have six jacks under the frame, two in front, two behind and two in the neighbourhood of the dash. There may be no resonant medium in the body and the body merely acts as a sound box collecting the note emitted by the scuttle, but tests on bodies with "R8S" Sonometer indicate that there is. We would like to make tests to discover which are the parts of the body which provide this resonance. The flat surfaces are usually the most suspected. In cannot be on the air in the body itself being resonant, like the air in an organ pipe or also the opening of all the windows would effect a cure. This it does not, but merely helps because some of the reverberating surfaces have been removed. These surfaces are capable of amplifying the sound emitted by the scuttle loud-speaker by reflexion without themselves in resonance. It may seem strange that, varied as the types of bodies are, they should all possess a part or parts which have approximately the same frequency. It might be explained this way. The resonance complained of appears to exist over a range of from 53 to 68 MPH. Some bodies may peak nearer one end of that engine speed it is quite a wide range; a range as wide as the other divergancies cover. e.g. Range of heights, 46ins. to 50 ins. Range of widths, 50ins. to 58 ins. Length of any single compartment 70ins. to 85ins. The roof, which is admittedly the chief cause of booming is of shallow thickness, hence it is very difficult to change its natural frequency by stiffening, as the effect of the added weight is almost enough to nullify the effect of the added stiffness. It would be helpful to make Br Sonometer tests on various bodies with the Resonator or see to see what natural frequencies exist in bodies of different types and makes both on Phantom 1. and P. 2. DIFFERENCES BETWEEN P.1. & P.2. Source of Energy. It is difficult to see why the driving vibration should not exist on both chassis. Transmission of Energy. The steering column fixing on P.1. is 15 ins. from | ||