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Impedance Measurement Sequence – Dual Channel Using Math Post-Processing
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 stepped sine sweep from 20 Hz to 20 kHz is played through the speaker while the signal across the loudspeaker terminals is recorded by Direct In 1 and the signal across the sense resistor (impedance box) is recorded by Direct In 2. A heterodyne analysis step is then applied to calculate the fundamental response from both inputs and a math post-processing step divides Fundamental A (speaker terminal voltage) by Fundamental B (voltage across sense resistor). A post-processing step corrects for the value of the reference resistor before displaying the final 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.
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.