Generator Noise Levels Explained: dB(A), Distance and How to Reduce Them

In Short

A generator noise level is the sound a running set produces, normally stated in dB(A) at a given distance. The figure only means something together with its distance and measurement point, and it falls with distance and with measures such as enclosures and silencers. A noise limit should always state both.

A bare diesel generator is one of the loudest machines on a site, and it runs for hours. Every permit, every neighbour and most customers therefore write a noise limit into the specification, and meeting it starts with understanding what the number means. This guide explains what a generator noise level means, why distance and the number of sets matter, and what each measure - enclosure, silencers, exhaust silencer, fan speed - contributes.

What the Numbers Mean

Noise is given as a sound pressure level in dB(A) - the A stands for a weighting that follows the ear - at a stated distance from the set. The same machine reads much lower further away, so a figure without its distance is useless. Makers also publish a sound power level, the total acoustic energy of the machine, which does not depend on distance and is what is used to work out the level at any point. The scale is logarithmic, so a difference of a few dB is a big difference in acoustic energy.

Two things are worth remembering: a small change in dB is hard to hear but stands for a lot of energy, and distance helps a great deal - the further from the set, the quieter it is.

Several Sets, Reflections and the Measurement Point

Several identical sets together are louder than one. A limit "at the fence" for a plant of many containers is therefore a far harder requirement than the same limit per container, and the specification should say which it means. Walls, buildings and hard ground reflect sound, and the height and position of the measurement point matter: a limit at a window on an upper floor is a different task from one on open ground. Night limits are often stricter than day limits.

Where the Noise Comes From and How to Cut It

The engine block and the exhaust outlet are the two big sources; the radiator fan is the third, and on a quiet set the loudest. The exhaust is treated with a silencer of the right grade, from industrial up to hospital. The engine is treated by housing it: a sound-attenuated canopy takes the edge off, an acoustic enclosure or container with lined walls and silencers on the air inlet and outlet does much more, and special designs go lower still.

The air path is the limit of every enclosure: the engine must breathe and the radiator must discharge, and sound travels with the air. Longer silencers cut more noise but make the fan work harder; where the enclosure cannot hold them, the radiator goes remote with slow fans and the enclosure only has to ventilate the engine heat. The remaining sources - the alternator, the structure, door seals - are handled by the enclosure design.

Specifying a Noise Limit

A usable specification gives the level in dB(A), the distance or the point, the measurement height, whether it is per set or for the whole plant, and day and night values if they differ. With that, AXON plans the enclosure, the air silencers and the exhaust silencer together and states the expected level with the offer. AXON builds acoustic enclosures and containers, air inlet and outlet silencers and exhaust silencers of every grade for generator sets of any make, as one acoustic package to the limit the site requires.

In short

dB(A) is only meaningful with its distance; makers also give the sound power
A few dB is a big change in energy; distance takes off a great deal
Several identical sets are louder than one; say whether the limit is per set or per plant
Exhaust silencers come in grades from industrial to hospital
A canopy takes the edge off; an acoustic enclosure or container goes much further
AXON designs the enclosure, the air silencers and the exhaust silencer as one package

What to send with an enquiry

Noise limit in dB(A), the distance or point, the height, day and night
Per set or for the whole installation, and the number of sets
Generator set make, model and the maker's noise data if available
Site layout: walls, buildings, neighbours, the fence
Where the radiator stands: on the set or remote
Space and transport limits for the enclosure

Send an enquiry Send us files

Questions we are often asked

How loud is a diesel generator?

A bare large set is one of the loudest machines on a site. A sound-attenuated canopy, an acoustic enclosure or an acoustic container each bring it down further, and special designs go lower still. The maker's data sheet gives the figure for a specific set.

What is the difference between dB and dB(A)?

dB(A) applies a weighting that follows the sensitivity of the ear and discounts low frequencies; noise limits and generator data are given in dB(A). Plain dB without weighting is used for detailed frequency data.

Can a generator meet a strict noise limit at a distance?

Yes, with an acoustic container, long air silencers and a critical or hospital grade exhaust silencer. It is a project task, not a catalogue item, and costs more than a standard enclosure. Send the limit and the distance.

Does a remote radiator make the set quieter?

It moves the fan noise - often the loudest source on an enclosed set - away from the enclosure, and a remote radiator with slow fans can be built very quiet. The enclosure then needs much less airflow and shorter silencers.

How is the noise level verified?

By measurement at the agreed point after commissioning, with the set at load, following the standard the specification names. The calculated level with the offer is what the measurement is compared against.