Higher Order Analog Butterworth Filter Designs, a Tutorial
- Make sure you have Java turned on in your browser.
- Enter high and low pass speaker impedances.
- Enter desired crossover frequency.
- On the second-order crossover calculator you must
select type of crossover.
- Click on the "calculate" button to get the answers.
Impedance is the nominal resistance of the speaker
(typically 4 Ohms).
Enter frequency in Hertz (not kHz).
Capacitor value(s) are given in millionths of a Farad
Inductor value(s) are given in thousands of a Henry
For the Zobel circuit, enter inductance in Henries
- First Order Crossover
- Second Order Crossover
- Third Order Crossover
- Fourth Order Crossover
- Zobel Circuit (Impedance
- L-pad Circuit (Speaker
First Order (6db/octave) Two-Way
- Phase shift on a first-order crossover is 90
Second Order (12db/octave) Two-Way
- 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
- Phase shift on a third-order crossover is
270 degrees (-90 degrees).
Fourth order (24dB/octave) Two-Way
- The phase shift on a fourth-order crossover
is 360 degrees = 0 degrees (no phase shift).
Zobel Circuit (Impedance
- 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
- 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.