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 sound resonance and 'booming' issues in modern car bodies compared to older designs.
| Identifier | WestWitteringFiles\V\March1931-September1931\ Scan083 | |
| Date | 25th March 1931 guessed | |
| (4) The Resonant Medium. Bodies on P.I. & P.2. do not differ greatly, but there are some fundamental differences. (a) The roof frequencies of modern bodies are lower, due to the lighter construction in the roof, and the desire to keep the roof as thin as possible. Roof sticks used to be 1.75ins. deep and may now be as little as .750in.s to 1.000ins ( we believe the sticks on 25GX. are very thin in depth.) (b) Due to the vogue of low cars passengers sit much nearer to the roof and more in the focus of the curvature of the rear quarter. This is bad for sound reflexion, and our coachbuilders know it. (c) There is more rounding of the roof and rear quarters into the back panel, which tends to cause the sound to be focused into the ear of the rear passengers. This can be experienced by sitting well forward and then moving gradually backwards and upwards into the parabolic shape. (d) Due to the call for these larger sweeps recourse has had to be made to panelling the rear quarters and back panel even though the car be fabric or leather covered above the waist-line. The smaller curves of two years ago could be produced by padding on wire netting over the sticks. We do not suggest that points in themselves explain anything but that there have been changes in a direction which would lead towards booming rather than from it. At the same time we admit that in the heavily built old bodies we certainly had booming; often alarming spells of it. A scientific investigation of bodies with the Sonometer as suggested by "RH{R. Hollingworth}" would no doubt throw a lot of light on this unfortunate feature of a body. EV.{Ivan Evernden - coachwork} [Handwritten] This memo is not intended to attribute the blame on either chassis or body individually. | ||