BIZOMAT MAKEOS · Engineering
Machinery Noise: Machine Level, Combined Sources and Distance
How loud is this machine on its own, how loud are several sources together, and how does level fall with distance?
Noise level of a single machine from the total and background readings by the handbook method, the combined level of up to four sources, and the free-field change in level with distance from a source.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Calculation | choice | Choose the calculation. |
| Total level, machine running | dB | Meter reading with everything running. |
| Background level, machine off | dB | Meter reading with the machine in question switched off. |
| Source 1 | dB | Level of the first source. |
| Source 2 | dB | Level of the second source. |
| Source 3 (0 = none) | dB | Level of the third source. |
| Source 4 (0 = none) | dB | Level of the fourth source. |
| Level at the reference distance | dB | Level measured at the reference distance. |
| Reference distance | m | Distance of that measurement from the source. |
| New distance | m | Distance at which the level is wanted. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Calculation
- What it is
- Which noise problem to solve: the level of one machine from readings with it running and stopped, the combined level of several sources, or how a level changes with distance.
- Units and format
- Choose one of 3 options from the list: Machine alone from total and background; Combine several sources; Change with distance.
- Example
- The form opens with “Machine alone from total and background” selected as a worked example. Choose the option that matches your case.
What this means: Total level, machine running
- What it is
- The sound level measured at the listening point with the machine of interest and every other source running.
- Units and format
- Enter a number in dB: decibels. The form accepts 0.000001 dB to 200 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 51 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the same meter position, frequency weighting and response setting for both readings.
What this means: Background level, machine off
- What it is
- The sound level measured at the same point with only the machine of interest switched off, leaving the background running.
- Units and format
- Enter a number in dB: decibels. The form accepts 0.000001 dB to 200 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 49 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- When total and background are within 3 dB of each other the result is very sensitive to reading errors, and the tool warns.
What this means: Source 1
- What it is
- The sound level of the first source on its own, measured at the point where the combined level is wanted.
- Units and format
- Enter a number in dB: decibels. The form accepts 0 dB to 200 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 85 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Decibels add logarithmically: two equal sources give about 3 dB more than one, not double.
What this means: Source 2
- What it is
- The sound level of the second source on its own, at the same point as the first.
- Units and format
- Enter a number in dB: decibels. The form accepts 0 dB to 200 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 82 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Source 3 (0 = none)
- What it is
- The sound level of a third source on its own at the same point; zero leaves it out.
- Units and format
- Enter a number in dB: decibels. The form accepts 0 dB to 200 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Source 4 (0 = none)
- What it is
- The sound level of a fourth source on its own at the same point; zero leaves it out of the sum.
- Units and format
- Enter a number in dB: decibels. The form accepts 0 dB to 200 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Level at the reference distance
- What it is
- The sound level measured at a known distance from the source, the starting point for working out the level at another distance.
- Units and format
- Enter a number in dB: decibels. The form accepts 0.000001 dB to 200 dB. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 90 dB as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Reference distance
- What it is
- The distance from the source at which the reference level was measured.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 10000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: New distance
- What it is
- The distance from the source at which you want to know the level.
- Units and format
- Enter a number in m: metres. The form accepts 0.000001 m to 10000 m. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4 m as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Each doubling of distance lowers the level by about 6 dB in a free field.
Method and formulas
- Machine alone: M = 10 log₁₀(10^(T/10) − 10^(B/10)), as in the handbook (51 and 49 dB give 46.7 dB).
- Combined: L = 10 log₁₀ Σ 10^(Lᵢ/10).
- Distance (free field, point source): L₂ = L₁ − 20 log₁₀(r₂ ÷ r₁).
- Example: 51 dB total with 49 dB background puts the machine at 46.671 dB.
Limitations
- Levels must be on the same weighting (for example dBA).
- Distance law holds in a free field; reverberant shops fall off more slowly.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Measure one machine’s noise in a busy shop
- Predict the level when another machine is added
- Estimate the level at a work station further away
Who it is for
- Health and safety officers
- Maintenance engineers
- Plant engineers
What you get
- Machine, combined or distant level
- Difference from the reference
- Measurement validity
Interpreting the result
- When background is 10 dB or more below the total, the total reading is effectively the machine’s level.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3455–3456. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Harmonics, hum and magnetostriction
In Distribution Transformers by the Numbers
What it covers: Why transformers hum at 100 Hz, how noise is specified and tested, how drive harmonics add winding loss and distort voltage, and how impedance trades fault level for distortion.
Method explained here · BIZOMAT original book
Decibels and how they combine
In Machine Noise Control by the Numbers
What it covers: Read sound levels in decibels, add and subtract sources correctly, rank what sets the level at a work position, and catch a noise budget spent on the source that did not matter.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Machinery Noise: Machine Level, Combined Sources and Distance calculator