Compressor room noise gets the same address assigned to it almost every time, namely the compressor package itself. Order an acoustic hood on that basis, measure again afterwards, and the disappointment is predictable. Little has changed at the workstation, because the decisive share arrives by a completely different route.

A compressed air installation radiates sound along several paths at once. As sta Group we have been planning noise control since 1986 for sites where people and machines share the same space. That is why no project of ours starts with a solution, but with the question of which component actually sets the level.

Compressor room noise rarely sits in the compressor alone

Airborne noise from compression, cooling and intake

At first glance the compression process seems to be the source. In practice the cooling fan, the intake, the blow-off valves and, on larger units, the dryer all contribute their own share. Each of these sits in a different frequency band and responds to a different measure.

On modern packaged units the cooling fan often governs the continuous level rather than the airend. It runs steadily, broadband and for long periods, while the compression itself is already damped behind the canopy. Screw compressor noise in particular tends to be dominated by the fan once the machine is enclosed.

Structure-borne noise through foundation and pipework

There is a second transmission path that a sound level meter picks up but few people attribute to the machine. Because the unit sits rigidly on the floor, vibration travels through the foundation into the building structure and through the connected pipework into distant areas.

Sheet metal cladding, ducts and pipe bridges then vibrate along and release the sound exactly where nobody suspects a source. Compressor room noise spreads across half the plant even though the machine stands in one place.

How loud is an air compressor in a real plant?

Air compressor noise depends first of all on the design. Piston units work with far more moving parts and reach 80 to 95 dB(A) uncanopied, while enclosed screw units compress without contact and land at roughly 62 to 75 dB(A) depending on size.

These figures are orientation values, not a commitment for your installation site. Manufacturers determine air compressor decibels under defined test conditions, at a fixed distance and without the influences of a real building. From 80 dB(A) European law requires preventive measures, from 85 dB(A) hearing protection becomes mandatory.

Why the data sheet and the workplace level differ

Four factors shift the result. Measuring distance, installation situation, reflections from walls and machine surfaces, and the actual operating point of the unit.

In a reverberant plant building the level at the workstation regularly sits several decibels above the brochure figure. A low air compressor noise level in the data sheet therefore says little about what your people hear every day.

Several compressors add up differently than you expect

Two equally loud units do not produce twice the level. Doubling the sound power adds around 3 dB, which the ear registers as clearly noticeable but not as twice as loud.

The arithmetic turns against you the moment you decide on measures. Enclose only the one machine out of three that annoys people most, and the summed level falls by less than 2 dB. The full cost lands, the perceptible relief does not.

For assessment purposes that means looking at the units together rather than individually. Two moderately loud machines produce more exposure at the same workstation than one considerably louder one, as long as both run through the whole shift.

Then there is the building itself. In large halls with hard surfaces a substantial share of the sound returns from walls and ceiling, so compressor room noise stays present where there is no direct line of sight to the machine. Where that boundary runs is set out in our piece on building acoustics vs. room acoustics.

Blow-off noise and leaks go unnoticed

The loudest point of a compressed air installation is often not in the plant room at all, but right at the workstation. Compressed air noise from blow guns used to clean parts is high-frequency, overlays other machinery and is felt as particularly sharp.

Low-noise multi-channel and multi-hole nozzles cut the level by up to around 10 dB(A), because they spread the air stream across several small openings and reduce turbulence. The IFA, the occupational safety institute of the German statutory accident insurance, recommends them after extensive testing. Set against any structural work, that is a very small step.

Why does this go unnoticed so often? Leaks work twice over. They produce a permanent hiss in the network and at the same time force the unit into load operation more frequently, which raises running hours and exposure. A leak survey therefore cuts level and energy cost in one go.

Low-noise nozzles as an immediate measure

Swapping nozzles costs a fraction of an enclosure and needs no production stop. It still rarely tops the list, because pneumatic tools are hardly perceived as part of the installation.

So check first which nozzles are actually in use before you think about enclosing anything. How many of them are low-noise types is something few sites can answer precisely. The result reorders some priority lists completely.

Measure before you enclose

Two quantities get confused regularly. Sound pressure level describes what arrives at a particular point in the room, sound power level describes what a machine radiates independently of its surroundings. Only the second makes two units genuinely comparable.

The established route is the enveloping surface method to ISO 3744, known in German practice as DIN 45635. The unit is measured at several points on a notional surface, which reveals the direction the dominant share comes from.

A measurement like this does not produce a report for the filing cabinet but a ranking. It shows which component contributes how many decibels and how much of that a given measure can realistically remove. That lets you estimate before the investment what will actually arrive at the workstation.

Cutting compressor room noise starts here in every project of ours. We measure on site with current equipment, evaluate the individual components and work out whether the compressor governs the workplace level at all or whether a neighbouring unit does. How such a survey runs is described in our piece on workplace noise measurement.

The options that actually reduce compressor room noise

Once it is clear which component dominates, the right option can be selected deliberately. Every approach below is a way to reduce compressor noise along one specific path. Each measure works against one transmission path and against no other.

The most common planning error is not about insulation but about air. A tight enclosure without a considered supply and exhaust path leads to heat build-up, loss of output and, in the worst case, shutdown. Noise control on a compressed air installation is always a cooling question as well.

For those openings there are proven components such as sound-attenuating ventilation systems, which pass the required air volume while holding the sound back. Which design suits your installation depends on layout, output and available space. An overview of the versions is on our page for compressor soundproofing.

Which combination is right in the end is decided by the measured share. Where structure-borne noise dominates, even the most elaborate enclosure achieves little, while a decoupled mounting works at comparatively low cost.

Cooling air and maintenance access

Service hatches, filter changes and oil checks have to stay reachable without dismantling anything. An enclosure that obstructs servicing is left standing open after a few months and then does nothing at all.

Our digital survey by 3D scan helps here. We manufacture elements to the millimetre and up to six metres long in our own plant, so the housing fits around the existing unit rather than replacing it.

When a separate plant room pays off

Where several units stand side by side, or the station sits close to permanently occupied workstations, the room solution usually beats individual enclosures. It gathers all sources together and creates a defined maintenance environment at the same time.

The effort for supply and exhaust air rises considerably though, because the entire cooling air volume has to be routed along sound-attenuating paths.

Where to start at your own installation

One order of work has proven itself in practice.

• Measure and locate. Only the split of the level into airborne, structure-borne and secondary radiation shows where an intervention is worth anything.
• Take the cheap immediate measures. Low-noise nozzles, tight fittings and a leak survey cost little and work at once.
• Plan the structural solution. Enclosure, room solution or screening for whatever remains after the first two steps.

This order protects you from the most expensive wrong decision, namely an elaborate enclosure for a component that does not govern the workplace level at all. Only measurement shows whether the compressor or another unit is setting the tone, and how much of the remaining compressor noise level can still be removed.

From projects in automotive, mechanical engineering and metalworking we know that most of these level problems can be solved with manageable effort once the cause is established. From analysis through design to installation we handle it from a single source. Talk to us if you want a reliable assessment of the level at your compressed air installation.