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Technical information: Suggested Zobel networks for Wavecor drivers
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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 resistor-capacitor (Req-Ceq) 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.
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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 (305KB 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.
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Driver model
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Req
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Ceq
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FR070WA01, 4 ohm *
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8.2 ohm
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5.6 uF
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FR070WA02, 8 ohm *
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22 ohm
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2.2 uF
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SW070WA01, 4 ohm
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3.9 ohm
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18 uF
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SW070WA02, 8 ohm
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8.2 ohm
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6.8 uF
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SW178WA01, 8 ohm
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6.8 ohm
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47 uF
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SW182BD01, 4 ohm
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4.7 ohm
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82 uF
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SW182BD02, 8 ohm
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8.2 ohm
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47 uF
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SW263WA01, 8 ohm
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8.2 ohm
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33 uF
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SW263WA03, 4 ohm
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5.6 ohm
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47 uF
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SW310WA01, 8 ohm
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10 ohm
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39 uF
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SW310WA02, 4 ohm
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5.6 ohm
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56 uF
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WF110WA01, 4 ohm
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3.9 ohm
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15 uF
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WF110WA02, 4 ohm
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4.7 ohm
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18 uF
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WF110WA03, 8 ohm
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8.2 ohm
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6.8 uF
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WF110WA04, 8 ohm
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8.2 ohm
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8.2 uF
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WF118WA01, 4 ohm
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4.7 ohm
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18 uF
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WF118WA02, 8 ohm
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8.2 ohm
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6.8 uF
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WF120BD01, 4 ohm *
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WF120BD02, 8 ohm *
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WF120BD03, 4 ohm *
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10 ohm
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10 uF
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WF120BD04, 8 ohm *
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22 ohm
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4.7 uF
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WF132TU01, 4 ohm
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3.9 ohm
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22 uF
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WF132TU02, 4 ohm
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3.9 ohm
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27 uF
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WF138WA01, 4 ohm
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3.9 ohm
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22 uF
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WF138WA02, 4 ohm
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3.9 ohm
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27 uF
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WF138WA03, 8 ohm
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8.2 ohm
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10 uF
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WF138WA04, 8 ohm
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8.2 ohm
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10 uF
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WF146WA01, 4 ohm
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3.9 ohm
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27 uF
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WF146WA02, 8 ohm
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8.2 ohm
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10 uF
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WF160WA01, 4 ohm
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3.9 ohm
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22 uF
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WF160WA02, 4 ohm
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3.9 ohm
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27 uF
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WF166TU01, 4 ohm
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3.9 ohm
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22 uF
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WF166TU02, 4 ohm
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3.9 ohm
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27 uF
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WF168WA01, 4 ohm
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4.7 ohm
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22 uF
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WF168WA02, 8 ohm
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8.2 ohm
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10 uF
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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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Copyright© by Wavecor Ltd., Guangzhou, China. All rights reserved.
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