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).
Report page discussing car body construction, frame rigidity, and the causes of acoustic booming.
| Identifier | ExFiles\Box 12\6\ 06-page037 | |
| Date | 25th March 1931 guessed | |
| (4) the dash and on P.2. it is 20 ins. There would be more pumping of the column at its fixing on the dash on P.2. (see Fig.1.) The frame of P.1. [strikethrough] has less torsional rigidity in front of the dash than P.1. and more than P.1. aft of the dash. Therefore with P.1. engine mounting it might be thought that the amplitude of the frame wave would be less than whena similar mounting is applied to P.2. This might be a reason for P.1. mounting not being a cure or as good as P.2. The Resonant Medium. Bodies on P.1. & 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 1.750 ins. deep and may be now as little as .750 ins. to 1.000 ins. (we believe the sticks on 25-EX. 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 reflection, 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 these 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 "R" would no doubt throw a lot of light on this unfortunate feature of a body. EV.{Ivan Evernden - coachwork} | ||