542 



BELL SYSTEM TECIIXICAL JOURNAL 



and with less distortion by providing the receivers with small tips 

 to insert in the ears but at a greater cost for additional recei\'ers. 

 It is perhaps better to use the tubing and earpieces of the ordinary 

 stethoscope as this is the equipment to which physicians are most 

 accustomed and to which the student must accustom himself for 

 future practice. The receiver case is provided with a spring clip 

 for attachment to the clothing. This allows full freedom of both 

 hands for manipulating the transmitter and the control switches of 

 the amplifier, taking notes, etc. 



The impedance of the output circuit depends upon tlic nuiulicr 

 of receivers in use and, for parallel connection, decreases as the num- 

 ber of receivers is increased. To care for the variable number that 

 may be used at different times, the output transformer has been 

 tapped and a three-way switch provided. By operating this switch, 

 the apparatus can be adjusted to a load varying from 1 to GOO reccixers 

 with a maximum transmission loss of 2.5 TV. 



8. FrEQUKNCV Ch.\R.ACTERISTICS of THK -STUTIlOPHONli 



The overall frequency characteristics of the stethophone, includ- 

 ing the transmitter, the amplifier, and the output receivers, are gix'cn 

 in Fig. 8. Two cur\es arc shown. The solid line cur\e reprtsenis 



♦40 lo.ooor 



C C C' c» 



niooCe c 

 MUSICAL MOTATIOM 



Fig. 8 — Fri'(|iiiMuy charadciist i<> nl tin >li ilici|il)i 



