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).
Theory of resonance exhaust silencers, including formulas and experimental results.
| Identifier | ExFiles\Box 104\2\ scan0035 | |
| Date | 1st July 1932 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Hm.{Capt. W. Hallam - Head Repairs} c. SG.{Arthur F. Sidgreaves - MD} wor.{Arthur Wormald - General Works Manager} c. RG.{Mr Rowledge} R.{Sir Henry Royce} c. HY.{Tom Haldenby - Plant Engineer} Ds. Hdy.{William Hardy} X5230. Hs{Lord Ernest Hives - Chair}/Hm.{Capt. W. Hallam - Head Repairs}11/ADS.7.32. RESONANCE EXHAUST SILENCERS. We have now done sufficient work on these to say something about them. The theory of a resonance silencer is briefly as follows. The dimensions of a single resonator, closed at its outer end, that will respond to a given tone can be obtained from the formula N = (A/2π) * √(C/Q) where N = frequency of the resonator A = velocity of sound C = conductivity of the passage connecting the capacity with the source of sound. Q = volume of the capacity C = πr² / (L + (π/2)R) where R is the rad and L is the length of the passage. We have proved by experiment on the road, that it is possible to tune out a carburetter roar at one particular road speed by having a container attached to the air intake and varying the capacity of the container by means of a moveable plunger. [Blueprint image of a resonator device] The difficulty about this is that on a carburetter there is often a wide range of roar and frequently two or more noisy frequencies separated by a considerable range. To silence such an intake by means of single resonators would be rather a formidable proposition. This is even more so on an exhaust silencer, where the exciting impulses are so much greater and boom periods occur at numerous speeds. | ||