COMBINATION HORN 



133 



other end opening in front or at the bottom of the cabinet within which it 

 is folded (Fig. 7.12). The labyrinth is a piston driven tube with absorb- 

 ing walls. At the first half wavelength resonance the velocity at the open 

 end is in phase with that at the front of the cone. The radiation, then, 

 from both sources is additive and the response is increased. An increase 

 in response can be obtained over about an octave. The rising absorption 

 of the tube lining with increase in frequency damps out the higher reso- 



ABSORBING WALL 



EQUIVALENT STRAIGHT PIPE 



(D20 

 a 



ul5 



SECTION THROUGH A-A' 



FRONT VIEW 



Fig. 7.12. Acoustical labyrinth loud speaker. The equivalent straight axis damped pipe is 

 shown above. The pressure response characteristic of the labyrinth loud speaker is labeled 

 B on the graph. The pressure response characteristic of the corresponding cabinet loud 

 speaker is labeled A on the graph. (After Olney.) (Courtesy of The Blakiston Company 

 from Olson and Massa, " Applied Acoustics.") 



nances. The transmission through the tube is very low above 150 cycles. 

 An anti-resonance occurs when the tube is one quarter wavelength long. 

 The deleterious effect of the fundamental resonance of the cone with its 

 suspension system upon the response may be eliminated by choosing the 

 constants so that fundamental resonance of the loud speaker coincides 

 with the quarter wavelength anti-resonance of the tube. The response 

 characteristic of a direct radiator loud speaker with and without a laby- 

 rinth is shown in Fig. 7.12. These characteristics show that the accen- 

 tuated response due to cabinet resonance has been eliminated and that the 

 low frequency range has been extended. 



7.13. Combination Horn and Direct Radiator Loud Speaker ^. — The 

 combination horn and direct radiator loud speaker consists of a horn 

 coupled to the back side of a direct radiator loud speaker mechanism and 



^ Olson and Hackley, Proc. Inst. Rad. Eng., Vol. 24, No. 12, p. 1557, 1936. 



