128 



DIRECT RADIATOR LOUD SPEAKERS 



loud speaker is mounted in a baffle, there exists a 180° phase difference 

 between the front and back of the cone. When the baffle is small com- 

 pared to the wavelength the system is an acoustic doublet. See Sec. 2.3. 

 In this frequency range the power output for constant velocity is propor- 

 tional to the fourth power of the frequency. When the baffle is large 

 compared to the wavelength, the two sides of the cone act independently 

 and the power output is proportional to the square of the frequency. See 

 Sec. 2,2. In the case of a mass controlled system the velocity is inversely 



100 

 FREQUENCY 



100 

 FREQUENCY 



Fig. 7.8. A. Pressure response frequency characteristics of a mass controlled direct radiator 

 dynamic loud speaker mounted in 2-, 3-, 4- and 6-foot square baffles. B. Response fre- 

 quency characteristic of a mass controlled direct radiator dynamic loud speaker mounted 

 in an irregular baffle. 



proportional to the frequency. Therefore, in the case of the large baffle 

 the output will be independent of frequency. See Sec. 7.2. However, 

 when the dimensions of the baffle are small compared to the wavelength, 

 the power output in the case of a mass controlled system is proportional 

 to the square of the frequency. In this range the low frequency response 

 falls off rapidly. The response characteristics of a mass controlled cone loud 

 speaker mounted in various sizes of square baffles are shown in Fig. 1 .%A. 

 The transition between doublet operation and independent operation is 

 quite marked. This transition point occurs when the dimensions of the 

 baffle are slightly less than one half wavelength. Above the transition 

 frequency the response is practically independent of the frequency. Below 

 this frequency the response falls off about 6 db per octave. 



In the case of a cone in a square baffle the path from the front to the 

 back is practically the same for all possible paths. Therefore, some pecu- 

 liarities in the response would be expected when the acoustic path from 

 the front to back is equal to a wavelength. At this frequency the sound 



