THE GRAMOPHONE — FREDDIE. 



221 



The disposition, too, of the various instruments of an orchestra in 

 the recording room is of the very highest importance if the best re- 

 sults are to be obtained. The wooden instruments are arranged about 

 4 feet from the mouth of the trumpet; behind them are the brass 

 instruments, and at the back the bass fiddles and drums. 



On the other side of the screen a horizontal table, carrying a wax 

 tablet, is rotated beneath the recording sound box at a fixed and uni- 

 form speed, generally about 76 revolutions per minute. As the table 

 rotates it also travels laterally at a fixed and uniform speed, being 

 carried on a revolving threaded spindle, and the wax tablet or blank 

 is thus caused to travel slowly under the stationary recording box. 

 The sapphire cutting point of the sound box is lowered so as to enter 

 the surface of the blank to the depth of about 0.0035 to 0.004 of an 

 inch, and as the ma- 

 chine runs it cuts a 

 fine spiral groove of 

 uniform depth, i-un- 

 ning from the cir- 

 cumference of the 

 blank to within 2 or 

 3 inches of the center, 

 according to the 

 length of the selec- 

 tion recorded. 



The exact construc- 

 tion of sound box 

 used for recording is 

 not disclosed by the 

 experts, but we may 

 take as illustrative 

 two forms which are covered by British patents, Nos. 659-01 and 

 627-01 (figs. 13 and 14). 



The turn table travels, as a rule, about 0.01 of an inch laterally for 

 every revolution, so that the spiral cut comes round about 100 times 

 in the width of 1 inch. It will thus be evident that the lateral undu- 

 lations of the sound line must be minute in the extreme as otherwise 

 the lines would at points break into one another. 



The recording blank is made of a soapy wax. Each laboratory has 

 its own receipt for the composition of the blank, but generally speak- 

 ing the compound is made up of stearin and paraffin. Many other 

 substances have been suggested, among which may be mentioned 

 barium sulphate, zinc white and stearin, ozokerit and paraffin. 



The consistency of the blank material must be such that it is stiff 

 enough to retain its shape when the sound groove is cut in it, and at 

 the same time it must not be so stiff as to offer any great resistance 



Fig. 13. — Recording sound box. A, stylus ; a, stylus bear- 

 ings ; B, diaphragm ; C, diaphragm holder ; D, flange of 

 sound tube ; E, counterweight. 



