Phase shift on a first-order crossover is 90
degrees.
Second Order (12db/octave) Two-Way
Crossover
Linkwitz-Riley crossovers match attenuation
slopes so that system response is flat at crossover point.
Butterworth crossovers yield to a peak at
the crossover frequency.
Bessel crossovers have a frequency response
between Linkwitz-Riley and Butterworth crossovers.
The phase shift on a second-order crossover
is 180 degrees (reversed polarity).
Third Order (18db/octave) Two-Way
Crossover
Phase shift on a third-order crossover is
270 degrees (-90 degrees).
Fourth order (24dB/octave) Two-Way
Crossover
The phase shift on a fourth-order crossover
is 360 degrees = 0 degrees (no phase shift).
Zobel Circuit (Impedance
Stabilization)
Even though speakers are rated at a certain
"resistance" (i.e. 4 Ohms), the actual impedance varies with frequency
(speakers have inductance). To compensate for the non-linearity of
speakers (on mainly subwoofers), Zobel circuits are used.
Re is the DC resistance of the woofer (can
be measured with an ohmmeter)
Le (or Lces) is the electrical inductive
equivalent of the driver.
L-pad (Speaker Attenuation)
An L-pad circuit will attenuate a
speaker.
L-pads keep the load "seen" by the amplifier
constant, affecting only the power delivered to the speaker. The
power delivered by the amplifier remains constant.
Since L-pads are made from resistors, it
does not induce any phase shifts, or affect frequency response.