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).
Vibration issues in high-frequency horn mountings and suggested solutions.
| Identifier | ExFiles\Box 59\3\ Scan189 | |
| Date | 2nd August 1932 | |
| Da{Bernard Day - Chassis Design}/EV.{Ivan Evernden - coachwork} from Hs{Lord Ernest Hives - Chair}/Wst. c. Ev.{Ivan Evernden - coachwork} c. E.{Mr Elliott - Chief Engineer} X6032. Hs{Lord Ernest Hives - Chair}/Wst.2/AD2.8.32. HORN MOUNTINGS. We thank you for your Da{Bernard Day - Chassis Design}/EV{Ivan Evernden - coachwork}2/M.4.7.32. Your query as to the discrepancy regarding horn mountings has raised an interesting point which must be borne in mind in regard to where and how we mount these high frequency horns. Apparently it is purely a question of the natural period of vibration of the mounting approximating to the sound frequency of the horn which is roughly 320 periods per sec. Messrs. Lucas informed us that we should probably have to experiment a lot in order to obtain the best mounting as it is impossible to foretell what the result will be with any semi-rigid mounting such as ours without trial. It is possible for the horn to set up vibrations for instance in the number plate and other frame fittings of a relatively large mass and area etc. They have had definite instances of this with other makers. From an examination of the drawings it would appear that the apron itself on the Peregrine should be stiffer than the 20/25, J.3 and the 40/50 as it has less area and has the same number of corrugations i.e. 10. As you state, it is an exact copy of the J.3 and 20/25 aprons. It will be seen, therefore, that to eliminate the noise it may mean a less stiffer apron on the Peregrine to approximate its natural period of vibration to the 20/25 which on Wob's car 17-GIV is O.K. as regards horn vibration. Alternatively, as the apron horn mounting appears to be so critical we suggest mounting the horn more rigidly to the frame and entirely insulated from the apron. A striking instance, quoted by Messrs. Lucas, regarding horn mountings was the 1932 Rover where the horn is mounted on the radiator Max stone guard. Although this mounting is extremely flexible and apparently a very poor mechanical support for the horn, contrary to expectation the horn gave no trouble as regards set up vibration. Hs{Lord Ernest Hives - Chair}/Wst. | ||