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).
Decibel calculations for sound intensity and car noise analysis.
| Identifier | ExFiles\Box 138\1\ scan0108 | |
| Date | 15th June 1934 guessed | |
| 20db.{Donald Bastow - Suspensions} = 10 log. P2/P1 - 10 log. P2/100. log. P2/100 = 2. P2/100 = 10^2 P2 = 10^4 P2 - P1 = 10^4 - 10^2 = 10^2 (10^2 - 1) = 9,900 units. Equal differences in decibel units of loudness do not represent equal intensity differences. Conversely one finds that a reduction in intensity by a half only results in a reduction in loudness by 3 decibels. n.db.{Donald Bastow - Suspensions} = 10 log. P2/P1. Now if P2/P1 = .500 n.db.{Donald Bastow - Suspensions} = 10 log. .500 = 10 x Ī.6990 = 3.010. Therefore if any intensity be halved, no matter what the magnitude, the reduction in loudness is always 3db.{Donald Bastow - Suspensions} It is due to this fact that it is always so difficult to reduce the loudness of a sound by reducing the energy of the vibration. Again, a much greater percentage reduction in loudness is produced by halving a small intensity than is produced by halving a larger one. For example. Intensity 80 units, db{Donald Bastow - Suspensions} = 10 log.80 = 19.03. units. Intensity 40 units, db{Donald Bastow - Suspensions} = 10 log.40 = 16.02. units. Intensity 20 units, db{Donald Bastow - Suspensions} = 10 log.20 = 13.01. units. Intensity 10 units, db{Donald Bastow - Suspensions} = 10 log.10 = 10.00. units. Intensity 5 units, db{Donald Bastow - Suspensions} = 10 log. 5 = 6.99. units. Attached is a report of tests made by the writer with the help of the Expl. Dept. using an Acoustic Meter made by the Standard Telephone Co. Tests were made in the Works, in the Offices and in various cars. We are arranging to discuss our results with the technical expert of the Standard Telephone Co. with a view to future developments. We feel that we should make a thorough attack on the question of noise in our cars because this is the one point on which we are no better than our competitors and in some cases we are worse. Most American cars are good from this standpoint. If we can satisfy ourselves that this meter does its job we w would like to buy it. EV.{Ivan Evernden - coachwork} | ||