Handbook for Sound Engineers

772 Chapter 22

(22-20)

where,

R 1 is the series resistor in ohms connected on the side of

the larger impedance;

R 2 is the shunt resistor in ohms.

The loss through the attenuator will be

(22-21)

22.2.2 Dividing Networks

Dividing or combining networks are resistive networks

designed to combine several devices or circuits, each

having the same impedance, Fig. 22-10A. The resistors

may be calculated with the equation

(22-22)

where,

RB is the build-out resistor in ohms,

N is the number of circuits fed by the source impedance,

Z is the circuit impedance in ohms.

The loss of the network is

(22-23)

where,

N is the number of input or output circuits.

Unused circuits of a dividing or combining network

must be terminated in a resistive load equal to the

normal load impedance.

This same circuit can be reversed and used as a

combining network. This circuit was often used in the

design of sound mixers.

Combining or branching networks may also be

designed as a series configuration, Fig. 22-10B. For

equal impedances the equation is

Figure 22-8. Attenuators connected in tandem.

p

p

p p

L T Bridged T

p

p

H Lattice O

A. Unbalanced

B. Balanced

Figure 22-9. Configurations of L-type networks.

R 1

Z 1 R 2 Z 2

p

R 1

Z 1 R 2 Z 2

p

R 1

Z 2 R 2 Z 1

p

R 1

Z 2 R 2 Z 1

p

p p

p

p

Z 1 = Z 2

Z 1 = Z 2

Z 1 > Z 2

Z 1 > Z 2

A. Between impedances of unequal value.

B. Between impedances of equal value.

D. Between impedances of equal value in

the direction of the shunt arm.

C. Impedance unequal and impedance

match toward the smaller of the two.

R 2

Z 1 Z 2

R 1

= -----------

dBloss 20

Z 1

Z 2

-----

Z 1

Z 2

-----–+ 1

©¹

̈ ̧

§·

= log

RB

N 1–

N 1+

=-------------Z

dBloss= 20 log N 1–