Overview
ISO 9295:2015 - "Acoustics - Determination of high-frequency sound power levels emitted by machinery and equipment" - defines standardized measurement methods for high-frequency sound power in the octave band centred at 16 kHz (11.2 kHz to 22.4 kHz). It specifies four complementary measurement procedures: three based on the reverberation test room technique and one using a free field over a reflecting plane. Test installation and operation follow the conditions given in ISO 3741 or ISO 3744 as applicable.
Key topics and technical requirements
- Frequency band: measurements cover the 16 kHz octave band (11.2–22.4 kHz) and are not frequency-weighted.
- Four methods:
- Measured reverberation time (direct method).
- Calculated air absorption (direct method).
- Reference sound source comparison (comparison method).
- Free-field over a reflecting plane (hemi-anechoic / free-field method).
- Instrumentation & calibration:
- Microphone and analyzer must provide a flat response for random incident sound in the 16 kHz band. After correction, tolerances shall be within ±1.0 dB across 11.2–22.4 kHz.
- Note: a microphone diameter of 13.2 mm or less is usually required to meet high‑frequency response.
- Calibration of the measurement chain and use of a calibrated reference sound source (where applicable) are required.
- Meteorological control:
- Temperature and relative humidity influence air absorption at high frequencies. The product h × (θ + 5 °C) shall not vary by more than ±10% during measurements.
- Recommended conditions: static pressure 86–106 kPa, temperature 15–30 °C, relative humidity 40–70%.
- Measurement practices:
- Mean time-averaged sound pressure levels in the reverberant field, reverberation times, room constants, and air absorption are used to calculate sound power.
- Specific requirements for microphone and equipment placement, measurement uncertainty, and data recording/reporting are specified.
Practical applications and users
- Who uses ISO 9295:2015:
- Acoustical engineers and test laboratories performing high-frequency noise evaluations.
- Manufacturers of machinery, electronic equipment, medical devices, and consumer electronics where high-frequency emissions (e.g., switching power supplies, high-speed printing) are relevant.
- Noise control consultants and regulatory bodies assessing product compliance or auditory/EMC interactions.
- Why use it:
- To obtain repeatable, comparable sound power data for high-frequency emissions.
- To support product design, noise mitigation, regulatory compliance, and supplier verification.
Related standards
- ISO 3741 - Precision methods for reverberation test rooms (sound power).
- ISO 3744 - Engineering methods for free field over a reflecting plane.
- ISO 6926 - Performance and calibration of reference sound sources.
- ISO 9613-1 - Calculation of atmospheric absorption of sound.
Keywords: ISO 9295:2015, acoustics, high-frequency sound power, 16 kHz octave band, reverberation test room, free field, microphone calibration, reference sound source.
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