Audio Engineering

722 Chapter 24

At or above the highest usable frequency, the impedance rise is again inductive. It
represents the effects of the voice coil inductance. Eddy currents, as such, or manifest as
skin effect and proximity effect , may also contribute to the inductivity. Inductive effects
are the cause ofback EMFs ( “ kick back ” voltages) that, unless damped, can upset sound
quality and can even destroy an unsound amplifi er design.

24.2.1.4 Passive Crossover Effects

Most high-performance speakers for domestic and small studio use contain passive
(unpowered) crossovers. Such enclosures are driven from a single amplifi er. Passive
crossover networks are “ in line with ” the drive units ’ impedances. The combination is
complex; it may increase or decrease peak current demand, hence loading. As an example

50.00

40.00

30.00

Ohms20.00

10.00

0.00 10 100

PA–LSZ–2.CIR Temperature  25

Inductive

Inductive

Inductive

Inductive

Resonance

Capacitative

Capacitative

Impedance

Phase

Resistive

1 K 10 K

100.00

60.00

20.00

Degrees20.00

60.00

100.00 10 100

Ph(v(2))

v(2)

Frequency

Frequency

1 K 10 K

Resistive

Figure 24.9 : The impedance of Figure 24.8 (upper graph), shown alongside the phase map

(lower graph), clearly shows the relationship between pure resistance and inductive and

capacitative phase—at least in terms of voltage. In some instances, a plot of current phase

might be more appropriate.