Declared noise should be read together with its magnitude and test phase. It is not necessarily the level a phone would record in a room, nor does it identify the cause of an abnormal noise.
Three ways to describe sound
- Acoustic power: describes the source’s emission under defined conditions.
- Sound pressure: describes the sound at a measurement point; it changes with distance and surroundings.
- Structural transmission: vibrations that reach other surfaces through supports and the building.
Decibels are a logarithmic scale. A numerical difference should not be read as a linear proportion of perceived loudness. Weighting and the test method must also match.
Compare the same phase
A slow-wash value is not directly comparable with a spin-cycle value. The European washing machine label identifies spin-cycle noise; other spec sheets must be reviewed according to their own scheme. Classes and thresholds belong to that system.
A phone app can capture rough changes in the same place, but the microphone, automatic adjustment, and position keep it from being directly equivalent to a standardized test.
What changes in a home
Wall reflections, furniture, distance, and floor affect perception. The suspension also affects transmission. That is why a motor type does not guarantee quiet operation in every installation.
New knocks, scrapes, or hums need to be diagnosed by phase and context. The label data describes emission conditions; it does not allow you to confirm bearings or other parts.
Note magnitude, weighting, and phase before comparing decibels; if any are missing, the comparison needs more context.