Serial Resonant Circuit Calculator

for Tube Amplifiers

Fezz Audio Silver Luna EL34 Valve Amplifier

The primary function of the circuit is to dampen and eliminate the effects of driver resonance on crossover networks.
If the driver has an undamped resonance peak wich is located less then two octaves from a highpass crosspoint, this circuit will greatly improve driver performance.

It's usefull on tweeters and midrange drivers.

It's possible to use the circuit on resonances in the lower octaves, but it usually calls for some extremely large value inductors.

Usage of impedance correction circuit: Let's say you have a loudspeaker with 6 Ohm, with a maximum impedance of 19 Ohm at 1200 Hz.
The impedance rise is no problem on a Solid-State-Amplifierd.

But, if you connect this speaker to a Tube Amplifier, then this impedance rise leads to an excessive level at 1200Hz.
Therefore, this impedance rise has to be compensated.

To achieve this, a R-L-C element should be connected in parallel to the crossover.

The R,C & L values are calculated by entering by entering the following data:
  • nominal impedance of the loudspeaker (Nominal impedance)
  • increased impedance that needs to be corrected (Maximum impedance)
  • frequency where the maximum impedance occurs (at frequency)
  • neighbouring frequency where the impedance drops exactly to the calculated value (½ the impedance)

Speaker impedance Re  Ω
  Max. Impedance   Frequency Impedance at   Frequency  
   Ω at  Hz  Ω at  Hz

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Values Impedance in Ω Rmin of Ω at Hz

* in Ohm: 10 Hz 12 Hz 15 Hz 20 Hz 25 Hz 30 Hz
L in mH: 40 Hz 50 Hz 60 Hz 70 Hz 80 Hz 90 Hz
C in uF: 100 Hz 120 Hz 150 Hz 200 Hz 250 Hz 300 Hz
  400 Hz 500 Hz 600 Hz 700 Hz 800 Hz 900 Hz
1000 Hz 1200 Hz 1500 Hz 2000 Hz 2500 Hz 3000 Hz
4 kHz 5 kHz 6 kHz 7 kHz 8 kHz 9 kHz
  10 kHz 12 kHz 15 kHz 20 kHz 25 kHz 30 kHz
* R is the sum of resistance-value (R) and DC-resistance of the inductor (L)

The Interrelationship Of Speakers And Amplifiers

Standard R-L-C Circuit

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