Silent range
Silent Diesel Generators
A silent diesel generator is the same engine, alternator and control panel as an open set, built inside an acoustic enclosure. The rating does not change — what changes is the enclosure, the air path, the silencer grade, the space the set needs and what it costs. A set quoted at 70 dB(A) at 7 m and one quoted at 95 dB(A) at 7 m can carry identical electrical data.
This page sets out how that number is produced, which figures are achievable at each power class, and how to decide whether a silent set earns its extra footprint on your site.
Enclosure
What is actually inside a silent canopy
Noise from a generator set travels by three paths: the engine block and its radiating surfaces, the cooling air that leaves the radiator, and the exhaust gas. A canopy only works when all three are treated, which is why weight and footprint both grow.
| Layer | Typical build | What it does |
|---|---|---|
| Outer shell | 1.5-2.0 mm galvanised steel, polyester powder coat 60-80 µm | Weather and impact protection; the mass that stops panel resonance |
| Acoustic infill | 50 mm mineral wool at about 60 kg/m3 for 72-78 dB(A); 100 mm at 80-100 kg/m3 for 65-72 dB(A) | Absorbs energy inside the cavity instead of letting it pass through |
| Perforated liner | 0.8-1.0 mm perforated sheet, 30-40% open area | Protects the infill while remaining acoustically transparent |
| Air path | Baffled intake and discharge, at least two changes of direction, louvre face velocity held to about 5-8 m/s | Removes direct line of sight for noise; a fast air path generates its own noise |
| Doors and seals | Lockable access doors with compression gaskets on all four sides | A 5 mm gap around a door can undo 100 mm of infill |
| Vibration isolation | Rubber or spring anti-vibration mounts under the base frame, flexible stainless bellows in the exhaust | Stops the base frame and the building acting as a loudspeaker |
| Exhaust silencer | Residential grade, 35-40 dB insertion loss; a second stage where the site limit is tight | Once the enclosure is closed, the exhaust is usually the dominant source |
| Radiator and fan | Enlarged core and slower fan to compensate for the higher air-path resistance | Required to hold the rating when the enclosure restricts airflow |
Noise figures
Sound pressure at 7 m by form and power class
The table below shows the range we see in commercial offers. The open frame and standard canopy columns are catalogue builds; the low-noise column is almost always a project-specific enclosure and should be confirmed against a stated test standard.
| Power class | Open frame | Standard canopy | Acoustic canopy | Low-noise build |
|---|---|---|---|---|
| 20-100 kVA | 78-86 dB(A) | 70-78 dB(A) | 62-70 dB(A) | 55-62 dB(A) |
| 100-300 kVA | 82-90 dB(A) | 72-80 dB(A) | 64-72 dB(A) | 56-64 dB(A) |
| 300-800 kVA | 85-93 dB(A) | 74-82 dB(A) | 66-74 dB(A) | 58-66 dB(A) |
| 800-2000 kVA | 88-96 dB(A) | 76-84 dB(A) | 68-76 dB(A) | 60-68 dB(A) |
The ranges overlap on purpose. A 100 kVA set with a thin shell can be louder than a 400 kVA set in a good enclosure, so the power class alone does not tell you the noise level. Ask for the figure at 7 m and at the distance of the nearest neighbour, not a single headline number.
Propagation
How the number falls away with distance
A generator set is small enough to behave as a point source across most of the distances that matter on a site. In free field the level drops by about 6 dB for every doubling of distance. Use the arithmetic below as a first check, then confirm it by measurement, because reflections and barriers move the answer.
| Distance from the set | Calculated level | What is usually there |
|---|---|---|
| 7 m | 70 dB(A) | Reference distance on the datasheet |
| 14 m | 64 dB(A) | Edge of a plant yard |
| 28 m | 58 dB(A) | Site boundary on a compact plot |
| 56 m | 52 dB(A) | Nearest building across a road |
| 112 m | 46 dB(A) | Residential area beyond the boundary |
Corrections a datasheet will not include: two identical sets running together add about 3 dB; a hard wall or a courtyard can add up to 3 dB through reflections; a solid barrier between set and listener typically removes 5-15 dB; and a tonal or impulsive character can attract a penalty under a local noise rule even when the dB(A) figure passes.
Specification envelope
What a silent build costs you in space and weight
| Item | Typical range | Why it matters |
|---|---|---|
| Enclosure protection | IP23 standard, IP44-IP54 for exposed coastal sites | Cable entries, glands and door seals all have to match the stated IP |
| Weight penalty | About 8-15% above the open set | Lifting plan, base tank design and foundation all follow this number |
| Footprint penalty | About 20-35% above the open set | A quiet set is a longer, wider set, and the air path cannot be blocked |
| Base tank autonomy | 8-12 h at 75% load on a bunded base tank | Longer autonomy moves the project to a separate bulk tank |
| Site ambient | Quoted at 40 °C and derated above it; 50-55 °C builds are available | An acoustic enclosure plus a Gulf summer is the design case, not the exception |
| Lead time | Typically 2-6 weeks longer than a catalogue canopy | Enclosure drawings are usually approved before the shell is built |
Choosing
Silent canopy or open frame
This is the comparison that decides most projects. Work down the left column and stop at the first row where the two answers differ.
| Question | Silent canopy set | Open frame set |
|---|---|---|
| Where does it stand? | Outdoors, on a roof, beside a building, in a residential compound | In a plant room or a dedicated acoustic house |
| Noise at 7 m | 62-76 dB(A) depending on class and build | 78-96 dB(A); the room, not the machine, makes it quiet |
| Weather and security | Protected against rain, dust and casual access | Needs a building; exposed to dust and to interference |
| Footprint | Larger, because the air path needs clear space at both ends | Smallest machine, but the room around it must be much larger |
| Maintenance access | Through lockable doors; some tasks need the canopy partly opened | Direct access from all sides |
| Cost | Higher set price, no building required | Lower set price, plus the cost of the room and its treatment |
| Typical use | Urban sites, hotels, hospitals, telecom, rental fleets | Factory plant rooms, basements, containerised and skid projects |
Questions
Questions we are asked about silent sets
How quiet can a diesel generator actually be?
Commercially, 65-75 dB(A) at 7 m is the normal acoustic canopy range across 100-1000 kVA. Below about 60 dB(A) at 7 m the enclosure becomes a project in its own right: thicker infill, a second silencer stage, a slower fan and often a larger radiator, with weight and footprint rising accordingly. A claim below 55 dB(A) at 7 m should come with a stated measurement standard and distance.
Is the dB(A) figure measured at 1 m or at 7 m?
Both appear on datasheets, and the difference is about 17 dB. A set quoted at 80 dB(A) at 1 m is roughly 63 dB(A) at 7 m, and a set quoted at 75 dB(A) at 7 m is about 92 dB(A) at 1 m. Check which distance applies before comparing two offers, then convert both to the same distance.
Does a silent canopy reduce the power output?
Not if it is built properly. The enclosure raises the resistance to cooling airflow, so the radiator and fan are resized to hold the same rating. Undersized enclosures are the usual cause of a set that runs hot in summer: the rating stays on the plate while the real capability falls away.
Will a silent set pass a 45 dB(A) night limit?
Only with attention to the whole path. If the set is 70 dB(A) at 7 m and the nearest neighbour is 60 m away, the arithmetic gives about 51 dB(A) before corrections, so location alone is not enough. The options that close the gap are a second silencer stage, a barrier wall, an acoustic door on the plant room, or moving the set to the far side of the site.
How much space does a silent set need around it?
Plan on at least 1 m of clear space at the radiator end and at the air intake, plus access on the door side for servicing. The exhaust must discharge away from windows and fresh-air intakes, and nothing — wall, parked vehicle or fence — should block the air path. Restrictions raise the temperature inside the canopy, and that temperature is what limits the real rating.
Related
Other form factors and ranges
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Diesel generator sets
How ratings, form factors and control options are defined.
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Containerized sets
ISO container packages with tank, cabling and controls inside.
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Open frame sets
Skid-mounted machines for plant rooms and acoustic houses.
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Trailer mounted sets
Mobile sets that move between sites on their own chassis.
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500 kVA class
400 kW, the most commonly specified silent set for facility duty.
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Request a quote
Send the noise limit, the distance and the load list, and we reply with the build.
Working to a noise limit?
Tell us the dB(A) figure, the distance it applies at, and whether it is a day or a night limit. That, plus the load list, is enough to size the enclosure.