A bare decibel number is ambiguous
Sound pressure at one position changes with distance and room reflections. Sound power describes the source using a defined measurement method. A-weighting, background correction, microphone geometry and operating state also matter. Supplier values cannot be compared when these conditions differ.
Define the operating modes
Measure fan-only where possible, preheat, temperature maintenance and cool-down. Record fan speed, heater cycling, shelf and accessory condition and whether food is loaded. Listen for tonal, rattling or intermittent events in addition to reporting an overall level. A lower average may still be objectionable if a narrow tone or vibration is present.
Build a reproducible specification
State the standard or internal method, room qualification, microphone positions, distance, background noise, stabilization time, mode, voltage and sample count. Define whether the limit applies to sound power or sound pressure. Retest after fan, motor, bearing, airflow path or sheet-metal changes.
Measurement reference
ISO 3744:2025 specifies an engineering method for determining sound power from sound pressure measurements on a surface around a source in an environment approximating a free field over reflecting planes. Product-specific test codes may add further conditions.
- ISO 3744:2025: https://www.iso.org/standard/80866.html