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.
Under what conditions was the published dB figure measured?
At 30 cm with A-weighting on a class-1 meter, with the background noise floor recorded and the unit at maximum speed; the published ceiling for this range is 60 dB. Those four conditions are the specification — the number alone is not. When comparing two suppliers, put their methods in adjacent columns before their results, because a different distance can move the reading more than a different motor. The noise measurement guide explains what each condition changes.
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.
The conditions every figure is measured under
| 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 worth defending
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.
Three questions for any noise claim
Why 30 cm, and what it assumes
The 30 cm distance assumes free-field propagation, where sound pressure falls by roughly 6 dB per doubling of distance [Beranek & Mellow, 2012]. Change the distance and the number changes with it, which is why the method is published rather than the figure alone.
References
- 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
Can I repeat your vibrator noise test in my own office?
Approximately. You need the same decibel test distance of 30 cm, a meter with A-weighting, and a room quiet enough that the background sits about 10 dB below the reading. Without those three the vibrator noise test you run is a different measurement rather than a disagreement.
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.
The method matters because the number travels without it. The measurement guide explains what changes when the distance or the weighting does, the technology page shows the bench, and the range states which figure applies to which model rather than to the catalogue as a whole.
Putting this reference to work
This page is the data. The four sections below are where it changes a decision: the terms it is quoted alongside, the guide that explains the reasoning, and the models the figures apply to.