Reference · Test method
Motor Noise Test Method
A noise figure without its measurement condition is not a specification. Here is ours, with the instrument class and the distance.
Most published noise figures in this category cannot be compared, because they are not measured the same way. A reading taken at one metre differs from one taken at 30 cm by roughly ten decibels; a reading taken at low speed differs from one at maximum by more than that. A number printed without a distance and a speed is marketing copy wearing a specification.
| Parameter | Condition |
|---|---|
| Weighting | A-weighted, the curve used for environmental and product noise assessment |
| Distance | 30 cm from the motor axis |
| Environment | Free field over a reflecting plane; the unit held clear of contact surfaces |
| Operating state | Maximum intensity, highest pattern, motor running continuously |
| Instrument | Sound level meter meeting IEC 61672 performance requirements |
| QC limit | Every unit checked against ≤60 dB(A); unusually quiet units are logged, not just loud ones |
Two choices in that table are worth defending. The distance is 30 cm rather than one metre because a buyer asking about noise is asking about the distance the product is actually used at; quoting the more flattering one-metre figure would answer a question nobody asked. And the limit applies to every unit rather than to a sample, because motor noise is the defect a customer notices first and cannot be argued with afterwards. The technology page carries the same figures with the test standards listed beside them.
- International Electrotechnical Commission (2013). Electroacoustics — Sound level meters — Part 1: Specifications, IEC 61672-1. Geneva: IEC.
- Beranek, L. L. & Mellow, T. J. (2012). Acoustics: Sound Fields and Transducers. Amsterdam: Elsevier.
- Rossing, T. D. (ed.) (2014). Springer Handbook of Acoustics, 2nd ed. New York: Springer.
Questions on this reference
Is 60 dB(A) actually quiet for this category?
It is below ordinary conversational speech and roughly comparable to a quiet office. Against the consumer-electronics convention of keeping powered personal devices below 65 dB(A), the range sits comfortably under it, and single-motor models run lower still at 45–55 dB.
Why is the measurement taken at 30 cm?
Because a figure without a distance is not a measurement. Thirty centimetres is near enough to be representative of use and far enough to be repeatable; the point is that the distance is stated, not that 30 is the only correct number.
Does the surface under the device change the reading?
Yes. A hard surface reflects and a soft one absorbs, and a device held in the hand is coupled to something that damps it. This is why a method has to specify the mounting, or two laboratories will disagree honestly.
Is the published figure a limit or an average?
A limit, applied to every unit at outgoing inspection — not a typical value measured once on a good sample. The distinction matters: a typical figure tells you what is achievable, a limit tells you what will not be shipped.
Next: why two decibel figures are rarely comparable — or see the published ceiling per model.