KEVOS® MAKEOS · Engineering
Machine Noise Acceptance Test (Background Correction, Distance, Limit)
From my sound level readings with the machine running and stopped, what is the machine’s own noise, is the background low enough for a valid test, and does it meet the limit at the specified distance?
Acceptance check of a machine against a noise limit: the machine’s own level from the total reading and the background with it stopped (as the machinery noise tool, machine mode), the validity of the test from the difference between the readings, the level corrected to the distance in the specification and to the operator’s position by the inverse-square law (as the machinery noise tool, distance mode), and the comparison with the limit.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Reading with the machine running | dB | Sound level with the machine running, at the measurement point. |
| Background reading, machine stopped | dB | Sound level at the same point with the machine stopped. |
| Measurement distance | m | Distance from the machine to the measurement point. |
| Distance in the specification | m | Distance at which the specification states its limit. |
| Operator distance | m | Distance from the machine to where the operator works. |
| Specified limit | dB | Highest machine level allowed at the specification distance. |
| Least difference between readings for a valid test | dB | Least difference between running and background readings for the result to be trusted (your test standard). |
Method and formulas
- Machine level L = 10 log(10^(T/10) − 10^(B/10)) (as the machinery noise tool, machine mode).
- Level at distance r = L − 20 log(r ÷ r₁) (as the machinery noise tool, distance mode).
- Valid if T − B is at least the least difference; meets the limit if the level at the specification distance is at or below it.
- Example: the machine alone is 87.251 dB; at 1 m it is 87.251 dB against 90 dB; the operator hears about 77.708 dB.
Limitations
- Steady noise, the same frequency weighting for both readings; tonal or impulsive noise needs more.
- Spreading as from a point source in open space; reflections in a room make far levels higher.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Accept a new machine against a noise specification
- Check a measurement made in a noisy shop
- Estimate the level at the operator position
Who it is for
- Safety officers
- Maintenance engineers
- Project engineers
What you get
- Machine level from the two readings
- Level at the specification distance and the operator
- Validity and limit check
Interpreting the result
- When the readings differ by less than about 3 dB the machine level cannot be separated reliably: reduce the background and repeat.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3455–3456. Topic reference; no source tables or recommended settings are reproduced.
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