First identify the decisive noise source
The total noise of an operation usually arises from several pieces of equipment working together. From the surrounding buildings, fans, ventilation outlets, compressors, cooling units, pumps, material handling, lorry traffic or operations inside the hall with the gates open may be audible.
Before designing a measure, it is advisable to find out:
- which piece of equipment is actually dominant in the protected space,
- whether the noise spreads through the air, through the building structure, or both,
- in which operating mode and at what time of day the situation is least favourable.
For basic diagnostics, you can use short-term indicative measurement, listening in the surroundings, switching individual pieces of equipment off one by one and comparing the noise levels of different operating states. For more complex operations, frequency analysis helps to show whether the noise contains pronounced low frequencies, tonal components or impulses.
An effective measure must correspond to the specific source and the way the noise propagates. There is no universal noise-control material suitable for every situation.
Which measures bring the greatest benefit
Priority is given to modifications directly at the source. Noise that does not arise does not have to be laboriously attenuated along its path to residential buildings.
Scroll the table horizontally to see all columns.
| Type of measure | Suitable use | Important condition |
|---|---|---|
| Repair and adjustment of equipment | Bearings, fans, gears, covers, vibration | Remove the technical defect and imbalance |
| Reduced speed | Fans, pumps, some production machines | Maintain the required output of the technology |
| Silencer | Intake and discharge of fans, ducts and outlets | Design according to flow rate and frequency spectrum |
| Acoustic enclosure | Compressors, units, pumps and smaller machines | Tightness, sufficient sound insulation and cooling |
| Anti-vibration mounting | Machines transmitting vibration into the structure | Correct stiffness of the elements and removal of rigid connections |
| Noise barrier wall | Outdoor sources and handling areas | Interrupting the direct line of sight between the source and the protected location |
| Building modification of the hall | Noise penetrating through the envelope, gates or roof | Check the weakest structural elements |
| Operational measure | Loading, gates, night operation, simultaneous operation of equipment | A clear and verifiable operating regime |
Before implementation, it is advisable to estimate the expected noise reduction. The declared sound insulation of a product or the attenuation of a silencer may not correspond to the resulting reduction in the protected space. The result is affected by leaks, flanking paths, the frequency composition of the noise and the simultaneous operation of other sources.
Ventilation systems, fans and outlets
In ventilation systems, noise can be radiated from the terminal outlet, the intake, the fan casing, the ducting and the structure on which the equipment is mounted. Before ordering a silencer, it is therefore necessary to determine the decisive propagation path.
A silencer inserted into the duct can significantly reduce noise carried by the air stream. Its design must take into account the required attenuation in the individual frequency bands, pressure losses, flow velocity and available space. An inappropriately sized silencer can reduce extraction performance or generate additional aerodynamic noise.
For outdoor outlets, changing the discharge direction, reducing the flow velocity or relocating the outlet to a more favourable position has also proved effective. Every change must be checked with regard to the function of the ventilation system, fire safety and any air protection requirements.
Acoustic enclosure for a compressor or machine
A good-quality enclosure must have sufficient surface mass, tight joints and properly resolved air inlets, cooling, cable penetrations and maintenance access. Every unattenuated opening can significantly reduce the effect of the whole structure.
Absorptive foam inside the enclosure reduces sound reflections and improves its internal acoustics. However, a thin layer of foam alone usually does not provide the necessary sound insulation. This is ensured mainly by a heavy and tight perimeter structure.
The enclosure must at the same time respect the cooling of the equipment. Ventilation openings can be addressed using attenuated ducts or acoustic louvres. An inappropriately designed enclosure can cause overheating, reduced output or a shorter service life of the machine.
Vibration and structure-borne noise
Resilient mounting of a machine helps when vibration is transmitted into the floor, steel structure, wall or roof. Anti-vibration elements must be designed according to the weight of the equipment, its speed and the dominant frequencies.
A common weakness is a rigid connection that bypasses the resilient mounting. Vibration can be transmitted through piping, cable trays, protective frames or rigidly connected ventilation ducting. A suitable solution therefore also includes flexible connectors, expansion joints and checking of all structural connections.
Low-frequency noise and vibration require particularly careful handling. Lightweight absorptive materials and ordinary thin enclosures tend to have limited effect at low frequencies.
Noise barrier wall
A noise barrier wall is effective mainly for an outdoor source located low above the ground. The wall must interrupt the direct line between the source and the protected location, have sufficient height and length, and be free of significant gaps.
The best effect is usually achieved when the barrier is placed close to the source or close to the protected location. A low wall placed in the middle of a large distance may bring little benefit. Limited effectiveness can also be expected for roof-mounted fans, tall outlets or sources with a pronounced low-frequency component.
The barrier material must have sufficient sound insulation. An absorptive surface on the side facing the source reduces reflections, but does not replace the necessary mass and tightness of the basic structure.
Noise penetrating from a production hall
When noise propagates through the building envelope, its weakest parts are decisive. These may be open gates, lightweight rooflights, ventilation louvres, leaks, penetrations or a lightweight roof structure.
Adding absorptive panels over the whole area inside the hall can reduce reverberation and improve conditions in the workplace. The effect on noise in the surroundings, however, depends on the construction of the envelope and the propagation path. Where noise escapes through open gates, changing the gate regime, creating an advance (vestibule) space or locally separating the noisy workplace is often more effective.
For loading and handling, improvement can often be achieved by a suitable location of the activity, limiting drops of material, using flexible stops and eliminating the noisiest operations at night.
Which modifications tend to be of little effect
A weak result can be expected from measures chosen without knowing the decisive source. Typical examples are sticking a small area of acoustic foam, a low barrier outside the direct propagation path, or enclosing a machine with large unattenuated ventilation openings.
It is also risky to carry out several minor modifications without verifying their overall effect. Reducing the noise of one piece of equipment may reveal another dominant source that was originally masked.
Before a larger investment, we recommend preparing an acoustic design or at least having the supplier's technical solution professionally assessed. The offer should include the expected attenuation, the conditions for achieving it and the parameters on which the design is based.
When to carry out noise measurement
Measurement makes sense when it corresponds to a specific objective. Before designing a measure, it can serve to diagnose sources and establish the baseline. After implementation of the measure, it verifies the improvement achieved. To demonstrate compliance with hygiene limits, the measurement must be carried out under representative, usually least favourable, operation.
According to Government Decree No. 272/2011 Coll., noise from stationary sources in the protected outdoor space of buildings is assessed during the day over the eight consecutive noisiest hours and at night over the noisiest one hour.
For ordinary noise from stationary sources, the hygiene limit is derived from a base level of 50 dB. For night time, a correction of −10 dB applies in the protected outdoor space of buildings, so the limit usually comes to 40 dB. For noise with tonal components, a further correction of −5 dB is added.
For measuring noise in the environment under Act No. 258/2000 Coll., on the Protection of Public Health, the holder of an accreditation certificate or authorisation is required. Indicative or diagnostic measurement can be used when looking for the source and designing measures, but for official documentation, measurement meeting the statutory requirements is necessary.
Recommended procedure after a noise complaint
After receiving a complaint, it is advisable to record the time, nature and conditions of the disturbing noise. This is followed by an inspection of the operation, diagnostics of individual pieces of equipment and a proposal of measures with an estimate of their effectiveness. After implementation, a control verification is carried out and, depending on the purpose, also accredited or authorised measurement.
Under the Act, the operator of a noise source is obliged to ensure by technical, organisational and other measures that the noise does not exceed the hygiene limits. The measures must therefore also work during normal and the noisiest permitted operation.
What you can send us and what we will verify
For an initial assessment, you can send us:
- photographs and the location of the main noise sources, technical data sheets of the equipment and a site plan of the premises,
- a description of operating hours, the noisiest activities, night operation and the course of any complaints,
- an earlier noise study, a measurement protocol, the opinion of the hygiene station or an offer for a proposed noise-control measure.
We will examine the likely sources and propagation paths of the noise, propose a diagnostic procedure and assess the suitability of the measures under consideration. We will help to determine what to modify before the next measurement and which operating conditions to capture during verification.
Follow-up diagnostics, control measurement and the protocol for the authority are provided as part of the service noise measurement and acoustics.