Impedance Measurement – Dual Channel Method Using Math Post-Processing

Impedance_measurement_math_postprocessing_outputThis 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.

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Perceptual Rub & Buzz

Perceptual Rub & Buzz ScreenshotThis sequence uses the CLEAR algorithm for perceptual Rub & Buzz measurement to detect AUDIBLE Rub & Buzz. It uses a simplified auditory perceptual model to measure the loudness of Rub & Buzz distor­tion in phons rather than the more traditional dB SPL and % distortion units. These better identify whether distortion due to manufacturing defects can be heard by the listener than conventional measurements. In addition to a result which corresponds more accurately to the human ear, this new test method also offers two significant advantages for use on the production line. It is less sensitive to transient background noises than traditional methods, therefore is reliable in noisy environments, and it is much simpler to set limits than when us­ing conventional distortion measurements. The sequence includes saved data that can be loaded from disk, so even if you don’t have a speaker handy you can still listen to the wav. file and see how SoundCheck displays the data.

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Impedance Measurement – Dual Channel Method Using Transfer Function

Impedance measurement - dual channel using transfer functionThis 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.

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