A compressor's noise is shown on its data sheet, on the "noise level" line, in dB(A). Our screw compressors are rated from 65 to 72 dB(A) depending on the model, with a tolerance of ± 2 or ± 3 dB(A). That figure does not tell the whole story: distance, the room and the number of machines change what you actually hear at the workstation.
What a dB(A) measures
The decibel measures sound level on a logarithmic scale. The "A" stands for a weighting that follows the sensitivity of the human ear, which hears low sounds less than mid-range sounds. It is the unit used to compare machines with each other.
Three rules follow from the scale itself. They are physical properties that apply to any machine:
- +3 dB(A) means twice the sound energy. Two identical compressors side by side do not make twice the decibels: they make 3 more.
- +10 dB(A) is perceived as roughly twice as loud. Ten identical machines add 10 dB(A) to a single one.
- Decibels never add up like litres. 70 dB(A) + 70 dB(A) gives about 73 dB(A), not 140.
Reading the "noise level" line on a data sheet
A data sheet gives a value or a range, followed by a tolerance. For a cautious estimate, take the top of the range plus the tolerance: a model rated "68 to 72 ± 2 dB(A)" can reach 74 dB(A).
These are the values from our data sheets:
| Model | Type | Noise level (data sheet) |
|---|---|---|
| S 55 and S 75 | Standalone screw, 5.5 and 7.5 kW | 65 to 68 ± 2 dB(A) |
| K 75 | 4-in-1 screw, 7.5 kW | 66 ± 2 dB(A) |
| S 110, S 150 and S 220 PM | Standalone screw, 11 to 22 kW | 68 to 72 ± 2 dB(A) |
| K 110 and K 150 | 4-in-1 screw, 11 and 15 kW | 68 to 72 ± 2 dB(A) |
| M 75 and M 220 | Mobile screw on receiver | 68 to 72 ± 2 dB(A) |
| L 110, L 150 and L 220 | 16 bar screw for laser cutting | 72 ± 3 dB(A) |
Two values can only be compared at the same distance and with the same measuring method. If a data sheet does not state the distance, ask for it before comparing two brands. Our article on reading a compressor data sheet explains the other lines.
Piston or screw, where the difference comes from
A piston compressor compresses air in pulses: every stroke of the piston creates a knock, which is the hammering sound you recognise in a workshop. Our E series compressors are belt-driven piston units on a receiver. Their data sheets give no dB(A) value, so we cannot give you a figure for the gap, only the fact that a piston unit is louder than an enclosed screw compressor.
A screw compressor compresses air through the continuous rotation of two rotors, with no back-and-forth movement, inside an acoustic enclosure. The sound is steadier and lower. The rhythm matters too: you hear a piston unit in bursts, every time it starts, while a screw compressor runs longer but more quietly. Our article on the difference between piston and screw compressors covers the rest of the comparison.
Distance, what physics says
In a free field, meaning outdoors and away from any wall, the sound level of a source drops by about 6 dB each time the distance doubles. This is a standard physical rule. Example: a machine measuring 70 dB(A) at a given distance gives about 64 dB(A) at twice that distance, and 58 dB(A) at four times.
In a closed workshop, that calculation no longer holds. Walls, floor and cladding reflect the sound. Beyond a few metres, the level drops much more slowly, sometimes hardly at all. Moving a workstation two metres further away in a bare room gains little. Putting a wall and a door between the machine and the team gains much more.
A worked example, one machine or two
A workshop needs about 2,800 l/min at 10 bar. Two options:
- Two S 110 at 10 bar, 1,400 l/min each, so 2,800 l/min. Each machine is rated 68 to 72 ± 2 dB(A). Two identical sources add 3 dB(A): at the same point, a cautious estimate gives up to about 75 dB(A).
- A single S 220 PM, 3,200 l/min at 10 bar, also rated 68 to 72 ± 2 dB(A). One source: up to about 74 dB(A), around 3 dB(A) less than the pair.
The flow is covered in both cases. Other criteria count too, such as backup in case of a breakdown, but on noise alone, one machine beats two.
The room, where you gain the most
- A separate room with the door closed. This is the most effective measure, far more than distance.
- Well-placed ventilation. The compressor needs fresh air and must get rid of its heat. The openings also let sound out: put them on the side away from workstations and reception. Never shut a machine in a box without ventilation, it would overheat.
- Stable installation on a floor that does not resonate, and a flexible connection to the network, so vibrations do not travel along the pipework.
- Covers closed and maintenance up to date. A machine with clogged filters is louder.
The general rules for siting a compressor are in our article on compressor room installation. Protecting staff from noise falls under the workplace rules that apply to your site: this guide does not give a limit.
What it means when choosing an AIRSTAHL compressor
- Machine in the middle of the workshop, no separate room: go for the lowest levels in the range, the S 55 or S 75 at 65 to 68 ± 2 dB(A), or the K 75 at 66 ± 2 dB(A) if you want the receiver and dryer built in.
- High flow: prefer one larger machine to several small ones, and install it in a separate room.
- Intermittent use with a piston unit: keep it away from reception and offices.
Our quiet workshop compressor page presents the suitable models. To size the flow, use the configurator, then tell us in your quote request where the machine will stand: we take it into account in our proposal.