Test & Measurement

Listen SoundCheck meets AES75-2022 (M-Noise) standard

21st November 2022
Mick Elliott

Listen says it is the first test and measurement company to automate measuring loudspeakers to the new AES75-2022 (M-Noise) standard for Maximum SPL.

This removes subjectivity, increases reliability, and saves time. The test sequence, developed for use within the company’s popular SoundCheck audio test and measurement system, is available free of charge on Listen’s website.

The AES75 test standard relies on multiple iterations of the same measurement at different levels to identify where the frequency response linearity, compression and coherence deviate from baseline levels.

When implemented manually, the user starts each individual measurement and subjectively compares responses to determine the next action.

Listen’s test sequence uses the same test method and stimulus, but carries out the entire test automatically, from initial baseline measurement to final burn-in analysis.

The SoundCheck software objectively analyses and compares each response signal using automated analysis steps and uses logic to drive the subsequent measurements in the procedure.

As well as saving time, this ensures more consistent results as it overcomes the subjectivity introduced in manual operation where the operator must interpret and compare real time spectrum analyser outputs.

The test sequence uses the M-Noise test signal, a stimulus specifically developed to emulate the dynamic characteristics of music.

It begins by verifying that the test is starting in the speaker’s linear region by using test signals well below the expected Max SPL to compare 2 baseline measurements of the speaker’s frequency response, linearity, coherence and signal to noise ratios. 

The test level is then sequentially incremented by 3dB. At each level, the response is compared to the baseline level until certain ‘stop conditions’ - differences in  frequency response linearity, compression and coherence - are met.

The level is then reduced to the last passing level and increased in 1dB increments to find the precise level at which the response deviates from the base level.

The device then enters a burn-in phase, where the stimulus is played for several minutes and again compared to the initial result.

This longer measurement also generates peak, RMS and A weighted RMS sound levels. If this response curve is within defined limits, it is recorded as the Max SPL curve determined by the standard; if not, then the device is cooled down and the tests repeated with a longer stimulus duration.

The only operator inputs required are the initial test level and the frequency range over which the measurements should be made.

The frequency range is included to ensure that the sequence is flexible for all products, but the user can easily adapt the sequence to already include this information, if preferred.

It should be noted that to run this sequence, SoundCheck Plus Version 20 with the Waveform Filter and Transfer function modules is needed.

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