Notch filter design calculator – for speakers
using the Inpedance Curve

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 4,,4 Ohm, with a maximum impedance of 24,7 Ohm at 820 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 820 Hz.
Therefore, this impedance rise has to be compensated.

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

The R,C & L values are calculated by entering by entering the following data:
  • DC Resistance of the loudspeaker (Re)
  • 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 impedance value.

Impedance peak at 820 Hz of 24 ohms

Speaker DC Resistance Re:  Ω
Max. Impedance of  Ω at the Frequency of  Hz,
with the Impedance of  Ω at the Frequency of  Hz

Reduce Impedance Range


Expand Impedance Range

Lowest impedance (Ohms) at   Hz

* in Ohm: L in mH: C in uF:
* R is the sum of resistance-value (R) and DC-resistance of the inductor (L)

Start Frequency: 10 Hz
Stop Frequency: 25000 Hz
Notch filter design calculator – for speakers using Re, Qes, Qms and fs

The Interrelationship Of Speakers And Amplifiers

Measuring Loudspeakers

Loudspeaker impedance measurement using a multimeter

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