766 



PROFESSOR JOHN G. M'KENDRICK 



1 1 inches in length, with a diameter at its wide end of 3 feet, and at its narrow end of 



| inch. 



The best results have been obtained with tin resonators. One large wooden 



resonator, shaped like a four-sided pyramid, formed of wood used for making wooden 

 organ pipes, 10 feet 7\ inches in length, each side being 3 feet in length at the base 

 and f inches at the apex, gave excellent results as regards volume and quality, but it 

 had a curious effect of damping or muffling the tones. Eesonators of vulcanite, papier- 

 mache were unsatisfactory. A conical resonator about 3 feet in length, 4 inches in 

 diameter at the wide end, and f inch at the narrow end, made of thin aluminium, gave 

 a remarkably clear ringing tone. Large resonators appear not only to give roundness 

 and volume to the tone, but also to quench many of the upper partials which cause the 

 hissing noises heard near the glass disk of the phonograph. In this way quality of 

 tone is improved. I have endeavoured to modify the form of the resonators in various 

 ways in the hope of altering the quality of the tone, but without success. 

 The resonators I employ have the following measurements : — 



No. 



Material. 



Length. 



Diameter at wide 

 end. 



Diameter at 

 narrow end. 



Name. 



1. 



Tin, 



8 feet 11 inches 



3 feet 



| inch 



Great resonator. 



2. 



Tin, 



6 feet 6 inches 



18 inches 



f inch 



Small resonator. 



3. 



"Wood | inch thick, 



10 feet 7|- inches 



3 feet 



f inch 



Wooden. 



4. 



Brass, . 



3 feet llf inches 



9f inches 



f inch 



Brass. 



5. 



Aluminium, . 



3 feet 1 inch 



7f inches 



f inch 



Aluminium. 



5. 1 have not been able to find any clear explanation of the mode of action of conical 

 resonators. Experience has shown that a cone is the best form both for a receiver by 

 which sound waves are transmitted to the phonograph disk, and for strengthening the 

 tone in reproduction. When used as a receiver in taking records, the cone should 

 be long and narrow, and, on the other hand, in reproduction, the best results are 

 obtained by increasing the length, and by increasing the diameter at the broad end. 

 Lord Eayleigh states that if the diameter of the large open end be small in comparison 

 with the wave length, the waves on arrival suffer reflexion, but by sufficiently prolong- 

 ing the cone, this reflexion will be diminished, and it will cease when the diameter of 

 the open end includes a large number of wave lengths. Further, he states that, apart 

 from friction, by diminishing the diameter of the narrow end, and at the same time 

 lengthening the cone, it would be possible to obtain from any given source of sound any 

 desired amount of energy, and to transfer this energy from the tube to the surrounding 

 air. This statement suggests the use of conical resonators much larger than those I 

 have yet used. I have observed that the tone is louder when the ear is placed in the 

 axis of the cone than when it receives the sound waves near the side, as if there were 

 a core of greater disturbance passing down the centre of the cone. 



