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).
Comparison and analysis of the Lucas horn against the Bosch horn, detailing construction, adjustments, and performance.
| Identifier | ExFiles\Box 59\3\ Scan072 | |
| Date | 10th September 1930 guessed | |
| -2- The Lucas horn is closely similar to the Bosch in construction. As received it was not adjusted to operate correctly. It was therefore set to approximately the same gaps as the Bosch. This resulted in a good loud note, the pitch being nearly the same as the Bosch, but lacking a sonorous quality characteristic of the latter horn. Particulars of the horn are :- Length (fore and aft) 8 1/2" Height 11" } less cover Weight 4 lbs 6 ozs.} and bracket. Coil resistance .81 ohms As set, the running current on 12 volts is about 5.0 amperes the current to break contact being 6.25 amperes and the force to break 63 lbw. These figures suggest that the setting is somewhat stiffer than the Bosch but in general, these horns can be adjusted to take more or less current at will, when the sound emitted is accordingly louder or softer. To alter the armature gap involves dismantling the horn. An adjustment for the moment of break during the stroke is provided consisting of an adjusting screw and lock-nut on the vibrating action. The same thing is achieved on the Bosch by means of a screw on the stationary part which enables the setting to be made with a screwdriver only whilst the horn is working. As regards the quality of the note on the Lucas horn, which is our chief concern at present, there are certain differences in construction which may account for the difference in tone. The Lucas trumpet is attached to the main body of the horn by a clamp in a way which leaves a number of holes at the root communicating with the outside. A draught can be felt here when operating. Stopping these holes with insulating tape gives the impression of slightly improved quality. The characteristic difference between the two horns however, is still evident when both trumpets are removed. The disc attached to the diaphragm in the Bosch has a rubber washer interposed between it and the diaphragm. On the Lucas there is no rubber interposed. | ||