Noise figures on generator quotes are easy to compare wrongly. A set quoted at “75 dB(A)” with no distance is
meaningless, because sound drops with distance. This guide explains why measurement distance
decides everything and how to read a noise specification like a buyer.
What buyers should know first
Manufacturers quote sound as dB(A) at a defined distance — most often 1 m (near
field) and 7 m (the typical site-boundary reference). The same machine will show a lower number at
7 m than at 1 m, so always compare at the same distance.
Why distance changes the number
| Distance | What it represents | Use |
|---|---|---|
| 1 m | Near-field, close to the set | Factory test, engineering |
| 7 m | Approximate site boundary | Planning / neighbour limit |
Sound falls roughly with distance (outdoors, not a perfect inverse square because of ground and reflections), so a
set that is 95 dB(A) at 1 m might be near 75–80 dB(A) at 7 m. Tests follow codes such as
ISO 3744 and the generating-set acoustic part of ISO 8528-10.
Open vs silent type
An open set is loud; a silent (canopy) type adds acoustic enclosure, intake and exhaust
attenuation. For schools, hospitals and residential sites, the silent type is usually the only way to meet a
boundary limit without a building.
Common configuration mistakes
- Comparing a 1 m figure from one supplier against a 7 m figure from another.
- Forgetting that the site boundary, not the set, sets the pass/fail limit.
- Ignoring intake and exhaust noise — the enclosure helps, but those paths still emit.
Procurement checklist
| Item | Confirm |
|---|---|
| Quoted distance | dB(A) at 1 m and at 7 m |
| Test code | ISO 3744 / ISO 8528-10 referenced |
| Site limit | Local boundary dB(A) and time of day |
| Enclosure grade | Open vs silent, with attenuation data |
Related equipment to compare
For noise-limited sites, start with the silent-type range and
school application sets. See the full product list or
contact us for a noise budget against your boundary limit.
Frequently asked questions
Which distance should I use?
Compare at the same distance the supplier states — prefer 7 m if you are checking a boundary limit.
Why is 1 m louder?
Sound is measured close to the source; it drops with distance, so 7 m reads lower than 1 m.
Do silent enclosures guarantee compliance?
They help greatly, but intake/exhaust paths and the actual boundary distance still decide the result.
What test code applies?
ISO 3744 for sound power/pressure, with the acoustic section of ISO 8528-10 for generating sets.
Can I site an open set in a city?
Rarely — most urban boundaries need a silent enclosure or a dedicated plant room.