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 white noise stimulus (10 Hz – 10 kHz) is played through the speaker while the signal across the amplifier terminals is recorded by Direct In 1 and the signal across the impedance box is recorded by Direct In 2. A transfer function analysis step is then applied to the recorded time waveforms to calculate the impedance curve. Subsequent post processing steps apply a frequency window, 1/24th octave smoothing and 1/24th octave resolution to 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 post processed impedance curves and results window.
Hardware
- Audio Interface (or AmpConnect ISC)
- Listen SC Amp (PN 4060) OR AmpConnectISC (PN 4042) OR discrete components (amplifier & impedance box (PN 4009 / 4010)
- Listen AmpConnect (PN 4042) or Crown D-45 PN 5600 (or similar)
Software
- SoundCheck 11.1 or later (p/n 1000 – SoundCheck Basic or higher)
- Transfer Function Analysis Module PN 2021
Impedance Measurement Set Up using discrete components
Impedance Measurement Set Up using SCAmp
Setup & Calibration -Discrete Components
- Calibrate the amplifier as instructed in the SoundCheck manual
- Connect Output 1 of your sound card to the input of the amplifier
- Connect the output of the amplifier to the “connect to amplifier” side of the impedance box
- Connect the loudspeaker to the “connect to speaker” side of the impedance box
- Connect Input 1 of the sound card across the terminals of the speaker under test. 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 speaker – wired for “floating” ground (no shield connection at speaker) for this connection.
- Connect the output of the impedance box to Input 2 of your sound card. Use a balanced cable (1/4” TRS) for this connection.
You are now ready to start the sequence.
Note: When first opening the sequence, you may be prompted to add calibrated signal channels named “Speaker” and “Sense Resistor”. These channels should be linked to Direct in 1 and Direct in 2 respectively.
Setup and Calibration – SC Amp
- Calibrate SC Amp as instructed in the SoundCheck manual
- Connect Output 1 of your sound card to the line input of SC Amp
- Connect the speaker under test to the SC Amp output
- Connect Input 1 of the sound card across the terminals of the speaker under test. 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 speaker – wired for “floating” ground (no shield connection at speaker).
- Connect Input 2 of the sound card to the SC Amp 0.1 V/Amp output. Use a balanced cable for this connection.
You are now ready to start the sequence.
