. Elements of acoustical engineering. Electro-acoustics; Sound. ACOUSTIC PHASE INVERTER 131 condition is fulfilled above the resonance frequency of the system. Below the resonance frequency the output falls off rapidly with frequency. A consideration of the equivalent circuit shows that the fundamental reso- nance of the system is influenced by both the acoustic capacitance of the suspension system and the acoustic capacitance of the cabinet volume. The response frequency characteristic with and without the back on the oj Mc Ma \ Ma^aa SECTION A-A FRONT VIEW Mc II Ma r^;^ ' 1 a ^^ A ' \
. Elements of acoustical engineering. Electro-acoustics; Sound. ACOUSTIC PHASE INVERTER 131 condition is fulfilled above the resonance frequency of the system. Below the resonance frequency the output falls off rapidly with frequency. A consideration of the equivalent circuit shows that the fundamental reso- nance of the system is influenced by both the acoustic capacitance of the suspension system and the acoustic capacitance of the cabinet volume. The response frequency characteristic with and without the back on the oj Mc Ma \ Ma^aa SECTION A-A FRONT VIEW Mc II Ma r^;^ ' 1 a ^^ A ' \ r / > ⢠-"^-*- z o 0. 10 q: â ^^"/ ^^, / ^i 0 A 1 1 100 FREQUENCY EQUIVALENT CIRCUIT Fig. Back enclosed loud speaker and the equivalent circuit of the acoustical system. Mc the inertance of the cone. Cas the acoustic capacitance of the suspension system. Ma and vaa the inertance and acoustic resistance of the air load upon the front of the cone. Cav the acoustic capacitance of the cabinet volume. The pressure p of the generator in the acoustic system is the force generated in the voice coil divided by the area of the cone. The pressure response frequency characteristic of the back enclosed cabinet is labeled B on the graph. The pressure response frequency characteristic with the back removed is labeled A on the graph. cabinet is shown by the graph of Fig. It will be seen that the re- sponse with the back enclosed cabinet is superior to the conventional open back cabinet. This is in general the case, providing the fundamental resonance frequency of the cone is made sufficiently low. The low fre- quency response of the open back cabinet falls off more rapidly with de- crease in the frequency than that of the closed cabinet. This is due to the fact that the open back cabinet acts as a doublet while the closed back cabinet acts as a simple source. See Sees. and The power output of a doublet for constant velocity is proportional to the fourth po
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