A diesel generator noise rating only means something when you know the measuring distance and the test standard. Buyers get burned because a bare 75 dB(A) with no distance is marketing, not a number you can permit against. This guide shows how to verify the claim before you commit.
What does a dB(A) rating actually tell you?
A rating with no measuring distance tells you almost nothing. Sound pressure drops about 6 dB each time you double the distance from the source, so a figure taken at 1 m and one taken at 7 m describe the same machine very differently. A credible rating states both the value and the meter distance, and the test standard used; suppliers commonly cite ISO 3744 for free-field or ISO 3746 for semi-reverberant measurement. If the listing gives only dB(A) and no distance, treat it as a headline, not a spec.
Does a low dB(A) number mean my site is compliant?
Usually not on its own. Local noise limits are set at the property boundary or a fixed offset from the set, not at 1 m or 7 m from the enclosure. To know if you are compliant you must compare the supplier's distance-corrected level to your local limit at the point that matters. Ask the supplier to project the level at your boundary distance, or provide the raw 1 m figure so you can apply the 6 dB-per-doubling rule yourself. A quiet enclosure means little if the boundary still breaches the limit.
How do I verify the noise claim before buying?
1. Require the factory test report, not a catalogue number.
2. Confirm the measuring distance and the test standard are stated on that report.
3. Confirm the rating covers the full package - enclosure, intake and exhaust silencer - not a bare engine.
4. Map the rating to your local limit at the boundary, not at the machine.
5. Get the verified figure written into the contract and the purchase specification.
If a supplier cannot produce a test report, that response is itself the answer.
When should I walk away from a noise claim?
- The supplier quotes only dB(A) with no measuring distance.
- The rating is for a bare engine, not the enclosed set you are actually buying.
- They reference a typical or approximate value and cannot supply a report.
- Your site is noise-sensitive (hospital, residential, hotel) and they will not project the level at your boundary.
Walking away from any of these protects you from a set that passes the brochure but fails the neighbour complaint.
The practical takeaway
Buy on the report and the distance, never on the headline number. For noise-sensitive sites, specify a silent or containerized package from the start rather than retrofitting silencers later. See silent diesel generator sets: https://linkpowergenset.com/en/products/silent-diesel-generator/ and containerized power systems: https://linkpowergenset.com/en/products/containerized-power-system/. For the application context, see hospital: https://linkpowergenset.com/en/applications/hospital/ and commercial buildings: https://linkpowergenset.com/en/applications/commercial-buildings/. LINKPOWER supplies the factory test report with measuring distance and standard; send your local limit and site layout and we will confirm compliance before you order.