STEADY STATE LOUD SPEAKER MEASUREMENTS 



153 



speaker similar to those shown on Fig. 5 for the horn type loud speaker. 

 Note for the same frequency the greater concentration of the sound 

 field in the case of the horn. This is due to its larger radiating surface. 

 From these data it might be inferred that if the sound field of a loud 

 speaker of either of these types is to be the same at all frequencies, 

 the size of its radiating surface must decrease as the frequency increases. 

 Indoor Measurements. — Making use of the above described outdoor 

 measurements as standards of comparison, response measurements 

 were made indoors on the same loud speakers and at the same relative 

 positions in the sound field in order to determine the magnitude of the 

 effect of reflections on such measurements. The room available for 



500 1000 



FREQUENCY 



Fig. 10 — Response-frequency characteristic of 115 cycle cut-off exponential horn 

 with moving coil type receiver. Measured in highly absorbing room 12 feet from 

 horn mouth on axis. 



this work was approximately 34' X 18' X 9'. The six bounding 

 surfaces of the room were covered with \" asbestos hair felt with heavy 

 monks cloth curtains loosely and irregularly draped over the walls. 

 The condenser transmitter and the loud speaker being measured were 

 located along the major axis equi-distant from and on opposite sides 

 of the center of the room and suspended about mid-way between the 

 ceiling and the floor. A moderately large room with the usual pre- 

 cautions to eliminate reflections was thus used. 



Fig. 9 shows the response frequency characteristic of the 3^" piston 



diaphragm loud speaker as obtained in this room with the condenser 



transmitter located on the diaphragm center perpendicular at a 



distance of 12'. A comparison of this curve with that of the same loud 



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