ACOUSTIC IMPEDANCE. 41 



m, md Equivalent mass of a vibrating diaphragm within its clamping 



circle (gni.). Equivalent mass of diaphragm in absence of 

 air (gm.). 



m Linear mass of air or other gas in acoustic conductor (gm./cm.). 



P Power at a point on an electric or acoustic conductor (watts 



or abwatts Z ) . 



p Ratio of equivalent displacement turns to 'exciting turns in a 



telephone receiver (absamperes/cm.). 

 T) = — Acoustic alternating pressure (deviation from quiescent hydro- 



S static pressure) at a cross section of an acoustic conductor 



(dynes/sq. cm. Z ). 



Po Hydrostatic pressure in quiescent air of acoustic conductor 



(dynes/sq. cm."). 



Po = yPo Adiabatic hydrostatic pressure in quiescent air of tube (dynes/ 



sq. cm.). 



TT = 3.141. . . . (numeric). 



q Quantity of electricity in an a-c. line conductor (rms. coulombs). 



Ri Electric resistance of a telephone receiver as measured with a 



continuous current (absohms). 



R, Rd Apparent resistance of a telephone receiver to alternating cur- 



rents when free and damped (absohms). 



r Mechanic resistance of a diaphragm excluding effects of mag- 



netic hysteresis (mech. absohms). 



r" Total mechanic resistance of a diaphragm at apparent reso- 



nance (mech. absohms). 



t' Effective mechanic resistance of a diaphragm due to magnetic 



hysteresis (mech. absohms). 

 r Linear resistance of electric conductor (ohms/km.). 



r Linear resistance of acoustic conductor (mech. obsohms/cm.). 



P Density of quiescent air or other gas in acoustic conductor 



(gm./c.c). 



S Surface area on one side of a diaphragm or cross-sectional area 



of an acoustic conductor (sq. cm.). 



Reciprocal of linear capacitance of electric conductor (daraf- 

 c km.). 



S = S Po Resilience force of acoustic conductor over its entire cross- 



section (dynes). 



Sd Stiffness coefficient of a telephone receiver diaphragm (dynes/ 



cm.). 



s' Apparent change in mechanic stiffness of a diaphragm due to its 



vibration in a permanent magnetic field (dynes/cm.). 

 o- Electric or acoustic load at the B end of a long conductor 



(ohms Z or mech. absohms Z ). 

 t Elapsed time from epoch (seconds) . 



t° Temperature in gas within acoustic conductor (deg. Cent.). 



Ao Oscillatory sharpness of resonance (numeric). 



V Velocity of transmission in electric conductor (km. /sec.) and 



in acoustic conductor (cm. /sec). 

 X, Xrf Reactance of a telephone receiver free and damped respectively 



(absohms). 



1 



s = - 



