


Technical information: Suggested Zobel networks for Wavecor drivers






In some speaker designs it is an advantage to use a so called Zobel network (figure on the right) to linearize the impedance of a drive unit. The effect of a correctly designed Zobel network is shown below on the impedance curve. Whether to use a separate network to equalize the high frequency impedance will depend on the crossover topology used, on personal design preferences, etc. A Zobel network is a series resistorcapacitor (ReqCeq) network that is connected in parallel with a loudspeaker driver in order to neutralize the effects of the driver’s voice coil inductance Le (see note below about Le). If a Zobel, or other kinds of networks, are used for driver impedance linearization/modification, it is important that the network be connected right on the driver terminals, between the driver and the crossover.










Note about Le: Normally the voice coil of a speaker driver is assumed to introduce a series inductance in the electrical equivalent circuit  most often called Le. If this assumption was true, the impedance curve of the drive would increase by exactly 6dB/octave at high frequencies. This is actually not the case as the impedance rise is closer to 3dB/octave. Read more about an alternative equivalent circuit here (270KB PDF). Although we are not dealing with a true inductance, the principle of neutralizing it using a resistor and a capacitor (zobel network) works rather well anyway.




Driver model

R_{eq}

C_{eq}

FR070WA01, 4 ohm *

8.2 ohm

5.6 uF

FR070WA02, 8 ohm *

22 ohm

2.2 uF

SW070WA01, 4 ohm

3.9 ohm

18 uF

SW070WA02, 8 ohm

8.2 ohm

6.8 uF

SW178WA01, 8 ohm

6.8 ohm

47 uF

SW182BD01, 4 ohm

4.7 ohm

82 uF

SW182BD02, 8 ohm

8.2 ohm

47 uF

SW263WA01, 8 ohm

8.2 ohm

33 uF

SW263WA03, 4 ohm

5.6 ohm

47 uF

SW310WA01, 8 ohm

10 ohm

39 uF

SW310WA02, 4 ohm

5.6 ohm

56 uF

WF110WA01, 4 ohm

3.9 ohm

15 uF

WF110WA02, 4 ohm

4.7 ohm

18 uF

WF110WA03, 8 ohm

8.2 ohm

6.8 uF

WF110WA04, 8 ohm

8.2 ohm

8.2 uF

WF118WA01, 4 ohm

4.7 ohm

18 uF

WF118WA02, 8 ohm

8.2 ohm

6.8 uF

WF120BD01, 4 ohm *



WF120BD02, 8 ohm *



WF120BD03, 4 ohm *

10 ohm

10 uF

WF120BD04, 8 ohm *

22 ohm

4.7 uF

WF132TU01, 4 ohm

3.9 ohm

22 uF

WF132TU02, 4 ohm

3.9 ohm

27 uF

WF138WA01, 4 ohm

3.9 ohm

22 uF

WF138WA02, 4 ohm

3.9 ohm

27 uF

WF138WA03, 8 ohm

8.2 ohm

10 uF

WF138WA04, 8 ohm

8.2 ohm

10 uF

WF146WA01, 4 ohm

3.9 ohm

27 uF

WF146WA02, 8 ohm

8.2 ohm

10 uF

WF160WA01, 4 ohm

3.9 ohm

22 uF

WF160WA02, 4 ohm

3.9 ohm

27 uF

WF166TU01, 4 ohm

3.9 ohm

22 uF

WF166TU02, 4 ohm

3.9 ohm

27 uF

WF168WA01, 4 ohm

4.7 ohm

22 uF

WF168WA02, 8 ohm

8.2 ohm

10 uF





Drivers marked * have very slight impedance rise at high frequencies, typically because the center pole is covered by a copper cap (for the exact purpose of keeping impedance rise low). For these drivers the Zobel network is not a perfect impedance compensation but the shown Req and Ceq values are considered best compromise.




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