. The Bell System technical journal . e tending to pull the armature further away fromits center position. The value of this torque for small amplitudes isproportional to the angular displacement. It is therefore seen that thisquantity is of the nature of a compliance but that the back force is in areverse direction to that required for a positive compliance. Design of the Reproducing Apparatus As the analogy between the mechanical and electrical filter is moreperfectly shown in the case of the reproducing equipment, its detailedquantitative description will now be given. Figs. 15 and 16 show
. The Bell System technical journal . e tending to pull the armature further away fromits center position. The value of this torque for small amplitudes isproportional to the angular displacement. It is therefore seen that thisquantity is of the nature of a compliance but that the back force is in areverse direction to that required for a positive compliance. Design of the Reproducing Apparatus As the analogy between the mechanical and electrical filter is moreperfectly shown in the case of the reproducing equipment, its detailedquantitative description will now be given. Figs. 15 and 16 show re-spectively a diagram of the reproducing system and its equivalentelectric circuit. From these diagrams it is evident which units in themechanical system correspond to the various electrical parts. Asthe series compliances c^, Ci and Co have been made so large that 516 BELL SYSTEM TECHNICAL JOURNAL the low frequency cut-off c^iused by them hes well below the lowfreq^iency cut-off of the horn, an inappreciable error is introduced in. Fig. 15—Diagrammatic sketch of the mechanical system of the phonograph using for design purposes formulas of low pass filters^-. The two for-mulas which will be used are as follows: TT \ nic (12) Wheref^ = cut-off frequency of a lumped transmission system in cycles per secondc = shunt compliance per section in centimeters per dynesm = series mass per section in grams ^ (13) where Zo^^ is the value of characteristic impedance over the greaterpart of the band range. -Campbell, G. A., On loaded lines in Telephonic Transmission, Phil. Mag.,March, 1903. , ^^ . So may be called nominal mid-shunt or mid-series impedance. 1 heir actualvalues in the transmission band being at any frequency/.. lid-series =\l— (^) Je mid-shunt = (i) RECORDING AND REPRODUCING OF MUSIC AND SPEECH 517 Equations (12) and (13) which form the basis of the design work con-tain four variables,/c, c, m and 2o. It is, therefore, necessary to deter-mine two of them by the phy
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