316 ARCHITECTURAL ACOUSTICS 



are pressed in thermoplastic material by the pressing matrix. The spiral wavy 

 path in the final record corresponds to that in the original soft wax record. 

 In reproducing, the record is turned at a constant speed by the turntable. 

 The stylus or needle follows the wavy spiral groove and generates voltage 

 corresponding to the undulations in the record. The output of the pickup 

 is equalized to compensate for the equalization in the original recording. 

 A low pass filter is used to attenuate the response above the upper fre- 

 quency limit of reproduction and thereby effects a reduction in the ground 

 noise. An attenuator controls the volume of reproduction. The atten- 

 uator is followed by the amplifier which drives the loud speaker. The 

 action of a reproducer in a living room has been considered in Sec. 12.2J. 



