Test System Instruments Requirements

Getting valid test results with an audio and acoustics test system requires the following prerequisites:

• Measured values are within the system dynamic range. A value smaller than the lower limit of the system dynamic range may lead to invalid test results. A value larger than the upper limit may lead to invalid test results as well as damage to the test system.
• The SNR requirement is met. The measured signal amplitude value should be much bigger than the system self-noise value. IEC 60268-5-6:2003 describes the measured signal amplitude value to be at least 10 dB bigger than the system self-noise value in speaker tests. In microphone tests, NI recommends the measured signal amplitude value to be 30 dB bigger than the system self-noise value.
• The results of repetitive measurements are stable. The difference between test results should be within a specific limit.
• The uncertainty of test results is appropriate. You can use the uncertainty value to modify the quality control range.

An audio and acoustics test system can satisfy the above prerequisites only if each test system instrument, including module, speaker, reference microphone, and chamber, meets their specific requirements.