STEADY STATE LOUD SPEAKER MEASUREMENTS 



149 



maintain its calibration closely, is the attenuator which involves only a 

 group of resistances. 



Outdoor Measurements. — As an illustration of those acoustic effects 

 involved in loud speaker measurements in a reffectionless medium, the 

 following response data obtained outdoors in an open field wall be of 



Fig. 5 — Polar curves showing response (expressed relative to the axis response) 

 of 115 cycle cut-off exponential horn with moving coil type receiver at various angles 

 from horn axis and 12 feet from the mouth. 



Fig. 6 — Polar curve showing response (expressed relative to the axis response) of 

 115 cycle cut-off exponential horn with moving coil type receiver at different angles 

 from axis and at a distance of 12 feet from center of horn mouth. 



interest. Two loud speakers having uniform sound power output 

 over a wide frequency range so that the dynamic characteristics would 

 not obscure the acoustic effects were used. The loud speakers were 

 placed at the edge of a skeleton platform appro.ximately 15' above the 

 ground and the condenser transmitter suspended at various positions 



