Impedance Measurement Sequence – Dual Channel Method Using Transfer Function
An alternative to the traditional SoundCheck single channel impedance measurement method
This sequence demonstrates an alternative to the traditional SoundCheck single channel impedance measurement method. A pink noise stimulus (10Hz – 10kHz) is played through the speaker while the signal across the amplifier terminals is recorded by Direct In 1 and the signal across the sense resistor is recorded by Direct In 2. A transfer function analysis step is then applied to the recorded time waveforms to calculate the impedance curve. The curve is then post-processed to calculate resonance frequency, maximum impedance and Q of the resonance peak. A set of arbitrary limits steps are also provided to generate pass/fail results. The final display shows the impedance curve and a results window.
- SoundCheck 18
- 2004 – Post Processing
- 2021 – Transfer Function
- Audio Interface – Listen AudioConnect or similar
- Power Amplifier – Listen SCAmp or similar
- Impedance Reference – Listen Impedance Box or SCAmp Impedance Reference Output
Hardware Setup and Calibration
- Calibrate the amplifier as instructed in the SoundCheck manual.
- Connect output 1 of your audio interface to the input of the amplifier.
- Connect the impedance reference (connection types will vary depending on reference type).
- Connect the amplifier output to the loudspeaker
- Connect input 1 of the audio interface across the terminals of the amplifier. Use a balanced cable with a ¼” TRS plug or XLR at the sound card and a ¼” TS(or dual, banana, alligator clips, etc.) at the amplifier – wired for “differential” ground (shield and ground tied to each other) for this connection.
- Connect the output of the impedance reference to input 2 of your audio interface. Use a balanced cable (1/4” TRS) for this connection.