RECENT ADVANCES IN WAX RECORDING 



165 



the ordinary range of room temperature. The "wax" must be 

 levelled in the recording machine with reasonable care. The stylus 

 must be sharp and so ground that the cut will be very clean. The 

 "wax" shaving is removed as cut by air suction. The operator is 

 aided in maintaining the correct depth of cut by the use of a so- 

 called "advance" ball which rides lightly on the "wax" and serves to 

 maintain uniform depth of cut in spite of small inaccuracies of leveling 

 of the "wax" or deviations from planeness. The "advance" ball is 

 adjusted relative to the stylus by observing the cut with a calibrated 

 microscope. A satisfactory operation of the recording machine re- 

 quires an ordinarily skilled mechanic with reasonable experience. 



.006 



5 — Recorder stylus. 



The rate of rotation is dependent upon the diameter of the record 

 groove which is determined primarily by the length of time which it is 

 desired to have covered by a single disc. The controlling element is 

 the linear speed of the groove past the recorder or reproducer. In the 

 Western Electric system the speed varies from 70 ft. to 140 ft. per 

 minute, in other words, of the same order of magnitude as with the 

 film record. The wave-lengths also are about the same as for a 

 sound record on a film. At the minimum linear speed the half wave- 

 length for a 5,000 cycle wave is .0014 in. If the minimum linear 

 speed is fixed at 70 ft. per minute and the groove spacing is fixed, 

 there is an optimum relation between the size of the record, the rate 

 of rotation and the playing time. This is illustrated graphically in 

 Fig. 6. 



After a record has been cut, the sound may be reproduced directly 

 from the "wax" by using a suitable pickup or reproducer. Ordinary 

 reproducers or pickups rest much too heavily on the records to be 



