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).
The limitations of an Acoustic Meter for measuring car noises, particularly low-frequency vibrations.
| Identifier | ExFiles\Box 138\1\ scan0115 | |
| Date | 1st August 1934 | |
| γ634 Sg.{Arthur F. Sidgreaves - MD} Rum Ev{Ivan Evernden - coachwork}7/DMc.L.1.8.34. Copy: L.H.S.{Lord Herbert Scott - Chair} (For circulation of C.S.C.) Wor.{Arthur Wormald - General Works Manager} Hs.{Lord Ernest Hives - Chair}✓ Hn.{F. C. Honeyman - Retail orders} E.{Mr Elliott - Chief Engineer} NOISE Before finally handing over the Accoustic Meter which has been very kindly loaned to us by The Standard Telephone Company, we discussed our tests with the Meter with their Mr.Tuckey. The writer and he together went out in a 25 h.p. Rolls-Royce Enclosed Limousine and jointly made some tests, the results of which are recorded at the close of this report. We are convinced that the instrument does measure the loudness of noise provided that the noise is a complex tone and that the predominating tone is of a medium pitch. If loudness of noise in itself were all that we are interested in, this instrument would fulfil our requirements. However, due to the peculiarity of the human ear and of ourselves as human beings, loudness alone is not the only factor. It has been authoritatively established that very low speed vibrations irritate mostly through feel, or shall we say physically, and not through the loudness of their noise. At about middle C the irritability is about 50% hearing and 50% feeling, whilst the high notes irritate mostly by loudness. Unfortunately for us most of the noises in a car, such as booms, roars and wind noises, are of a pitch which fall into the low category. Again, the instrument measures noise in decibels and whilst it is established that the smallest increase in noise which the human ear can appreciate is two decibels, it is certain that the human nature can appreciate much less than one decibel of difference in loudness if the note in question is of a low pitch and irritates more by feel than by hearing. We agree that the instrument does not give us all we want, but we have failed to find anything which is better - in fact the science of the measurement of sound has only been | ||