CORRECTIVE NETWORKS 67 



the mechanical compliance multiplied by the square of the area of the dia- 

 phragm. It will be seen that this system will not transmit a steady flow 

 of a gas in the same way that the electrical circuit of Fig. 4.6£ will not 

 transmit direct current. Since the reactance of an acoustic capacitance 

 is inversely proportional to the frequency, the volume current transmission 

 will increase with increase of the frequency as shown by the characteristic 

 of Fig. 4.6//. 



H. Inductance and Capacitance in Series, in Series with a Line and the 

 Mechanical and Acoustical Equivalents. — Figure 4.6/ shows an inductance 

 and capacitance connected in series in a line. The mechanical and acous- 

 tical equivalents are shown in Figs. 4.6/ and 4.6/C. At low frequencies 

 the three systems behave the same as Figs. 4.6£, 4.6/^ and 4.6G and the 

 transmission is small. At high frequencies the systems behave the same 

 as Figs. 4.6yf, 4.65 and 4.6C and the transmission is small. At the res- 

 onant frequency of the inductance and capacitance the impedance is zero. 

 Therefore, the attenuation is zero at thi^ frequency. At the resonant 

 frequency of the mass and compliance, Fig. 4.6/, there is no attenuation 

 because the impedance presented by the mass and compliance is zero. 

 At the resonant frequency of the inertance and acoustic capacitance. Fig. 

 4.6i^, the impedance of this system is zero and there is no attenuation. 

 The transmission characteristics of the three systems of Figs. 4.6/, 4.6/ 

 and 4.6/C are shown in Fig. 4.6/,. 



I. Inductance and Capacitance in Parallel, in Series with a Line and the 

 Mechanical and Acoustical Equivalents . — Figure 4.6M shows an induc- 

 tance and capacitance in parallel connected in series with a line. The 

 mechanical and acoustical equivalents are shown in Figs. 4.6A^ and 4.60. 

 At low frequencies the systems behave the same as Figs. 4.6^/, 4.65 and 

 4.6C and the attenuation is small. At the high frequencies the systems be- 

 have the same as Figs. 4.6£, 4.6/^ and 4.6G and the attenuation is small. 

 At the resonant frequency of the inductance and capacitance, Fig. 4.6M, 

 the impedance is infinite and there is no current transmission. At the 

 resonant frequency of the mass and compliance of Fig. 4.6A^ the input to 

 the spring does not move and there is no velocity transmission. At the 

 resonant frequency of the inertance and acoustic capacitance the vol- 

 ume current " pumps " around this circuit and there is no volume cur- 

 rent transmission. The transmission characteristics of the three systems 

 of Figs. 4.6M, 4.67V and 4.6P are shown in Fig. 4.6/,. 



J. Resistance in Series with a Line and the Mechanical and Acoustical 

 Equivalents. — Figure 4.7y/ shows a resistance in series with a line. The 

 attenuation will be e:reater as the resistance is made larger. Tn the same 



