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 a Lucas buzzer horn against a Bosch horn.
| Identifier | ExFiles\Box 59\3\ Scan071 | |
| Date | 10th September 1930 | |
| COPY. AD.65. 10th September, 1930. LUCAS BUZZER HORN COMPARED WITH BOSCH. Mr.Thacker of the Lucas Co. left with us a horn which represents an endeavour to produce a note similar to that of the R.Bosch model UK.12 an example of which we also have for comparison. The Bosch horn complies substantially with the description given in AD.36 of 12.6.29. The following particulars were found :- Length (fore and aft) 9¾" (with bracket) Height 10" Weight 4 lbs 7 ozs. Coil resistance .64 ohm. The adjustment, as received, was not altered and the following further particulars were observed :- An increasing current was passed through until the points just broke contact. This occurred at 4.25 amperes. The stroke of the armature from rest to break contact was approximately .018" and the further stroke to contact with the core about .005". The force required at the armature to break the contacts was 56 lbs. On 12 volts the working current was 3.0 amperes and the pitch frequency 300 periods per sec. On this type of horn there is no diaphragm striker, the armature being attached direct to the centre of the diaphragm. The latter, moreover, is circularly corrugated which increases the stiffness and accounts for the large force required to deflect it. The diaphragm carries in addition to the armature, and on the opposite side, a stiff metal disc a little smaller than the diaphragm itself clamped at the centre and free at the edge. The frequency of the note produced is approximately the natural frequency of the diaphragm assemblage as can be heard by tapping the body of the horn without current applied. The exact function of the diaphragm disc is not clear, it may act in some way as a valve at the root of the trumpet. | ||