Learning Centre Noise
Here we share our knowledge, expertise and 35 years of practical experience in noise reduction and acoustics.
Our learning centre aims to give you insight and overview through general descriptions, thumb rules, tips, and recommendations.
If you have a specific project in mind, please get in touch with us for a non-committal talk.
What is Noise Reduction and Acoustics?
Despite many years of focus from both authorities and the labour market, noise remains a challenge at many workplaces.
With this learning centre, we try to provide inspiration for working with noise, including touching on some options for reducing noise.
Machine enclosure with an acoustic ceiling and plenty of access via doors and gates.
Short animated video on noise reduction.
Short video on noise reduction.
About noise policy
It starts with you formulating the overall objective, which could be:
“No employee should be harmed or inconvenienced by noise at the workplace”
To do this, you should set a number of objectives, which should be related to the company’s own minimum
requirements and within legislation.
In most of the EU, it is agreed that the following categories and ranges are realistic for most industries, and
for the top category, the limit value 85 dB(A) MUST be respected.
dB(A) is weighted sound in Decibels over 8 hours, LAEQ
To achieve the noise targets, you should have a noise strategy that includes:
- Management support – at all levels
- The employees of the safety organisation have a key role in finding solutions
- Acoustics expertise is incorporated
- Noise requirements are part of machinery procurement and when rebuilding or adding an extension
- Hearing protectors seen as temporary solution
And you add systematics to your noise reduction through:
- Mapping of current noise
- Action Plan
- To apply both own knowledge and acoustics expertise in the solution work
So you reach your noise goals.
We are happy to act as acoustics experts in your work with noise. Remember that it is non-binding.
Note the office upstairs noise and heat muted production plant
Hearing protectors are mandatory if the noise is above 85 dB(A)
Machine enclosure with door and gate access
When purchasing machines
Machine enclosure in the same colour as the machine
Machine enclosure of a turret punching machine.
It would help if you prevented noise even before machines are purchased, i.e. before the supplier produces them.
It's much cheaper to noise reduce the machine itself than to noise reduce it when it's on your premises.
You can achieve this by setting requirements for how much noise the machine can make at the point of purchase.
Legal requirements for the purchase of machinery
There is no legislation on how much noise a machine can make, but there is legislation that the supplier must indicate how much noise the machine makes.
This is described in the Machinery Directive, which states that the noise level must be declared:
- If the sound pressure level exceeds 70 dB(A) at the operator’s workstation
- If the peak value of the sound pressure level exceeds 130 dB(C)
- If the sound power level at the workplace exceeds 85 dB(A)
The European CEN has defined how these measurements should be made for a wide range of machine types. If the machine type is not available, the supplier must choose an appropriate measurement method.
The noise levels indicated by the supplier are shown in the machine’s operating instructions.
Use of noise data from the user manual
The instruction manual data can be used with some caution to assess the noise levels of the machine, however, it should be noted:
- Are your operations the same as those used during the supplier’s measurement of noise?
- Is the measurement of noise defined by CEN or has the supplier chosen it own method of measurement?
- Is the room where the machine will be placed comparable to the room where the supplier had conducted its measurement?
- Do you use the machine in the way it is generally used according to the supplier?
Normally, however, the data in the instruction manual can be used to compare the noise levels of different machines.
As a result, we recommend a certain safety margin of 5 dB, for example. In other words, you should require a noise level that is 5 dB below the data in the instruction manual.
The supplier must demonstrate compliance, preferably with an independent noise measurement, which must be stated in the procurement contract.
We are happy to act as acoustics experts in your work with noise. Remember that it is non-binding.
When workspaces need to be furnished
Noise problems can be prevented by appropriate design and layout of the workspace/room.
Here we will look at
- Construction process
- Placement of noisy machines, etc.
- Acoustic regulation
- Sound insulation
- Noise from fixed building installations
For refurbishments and new buildings, noise should be taken into account from the outset. This ensures that an acceptable sound environment can be created with the minimum of resources, without conflicting with other considerations, such as architectural issues.
A building process consists of:
- Project planning
- Control and acceptance
The planning phase defines what is to be built and the conditions for it. The quality of the acoustic solutions must be determined already at this stage. Requirements should be set for building layout, acoustics, sound insulation, technical installations and approval.
- The safety organisation should be involved from the start. In our experience, they contribute to the solutions.
- External experts should be brought in where one own competency is not sufficient.
- The Danish Working Environment Authority’s guides, checklists, etc. can provide inspiration.
- Consulting engineers and architects play an essential role in this phase, and it should be ensured that acoustics and sound insulation are included in the chosen solutions.
- The tender material should include acoustic and sound insulation requirements and how they are measured.
In the design phase, the technical solution is specified and, as this is often the responsibility of the external supplier who won the tender, your company should be involved in discussions so that acoustics and sound insulation are specified at the right level.
In the execution phase, the noise conditions of the buildings should be clarified. Thus, the task here is to ensure that all work is carried out as prescribed. Even a small failure, such as a poor seal, can lead to a significant deterioration in sound insulation.
Control and acceptance
At this stage, the building is approved and it should be ensured that acoustic and sound insulation requirements are also met.
Or contact us if you want to know more about the design of the workplace.
Many of our customers are schools
Shielding of welding departments
Acoustic wall in the break area
When noisy machines need to be installed
Noisy and quiet activities should be located as far apart as possible.
Noise can be reduced by locating noisy machinery and activities appropriately. We recommend the following principles:
- Distance – Place the noisy machines as far away from the other activities as possible. Sound pressure drops 10-15 dB over 10 metres if the room is acoustically damped correctly.
- Concentration – By concentrating the noisy machines in one place, the overall sound pressure in the room decreases, even though the sound pressure at the machines increases.
- Screening – By placing shelving, storage and other screens between noisy and non-noisy activities. The larger and the more dense, the greater the effect.
- Absorption – Placing noisy machines up against walls and in corners with good absorption reduces radiated sound and makes it easier to effectively shield the machine. It is a prerequisite that there is good absorption on walls and ceilings, otherwise, the opposite effect is achieved.
Feel free to contact us if you want to know more about the placement of noisy machines.
What are baffles/wall partitions?
Baffles are a generic term for fixed or mobile screens between noisy and quiet activities, often called wall partitions, as they can screen out things beyond noise.
Especially if the sound is high frequency and you can place the wall partition close to the noise source, you can often reduce the noise simply by using a wall partition.
Requirements for free-standing screen
To achieve maximum use of the screen, one must avoid that the sound is reflected from the confinement surfaces of the room.
- The most important thing is that the ceiling is sound-absorbing, at least in an area above the screen.
- The screen is placed as close as possible to the noise source, alternatively as close as possible to the
- The side of the screen facing the noise source should be absorbent.
- The screen must be at least high enough to break the line of sight between the noise source and receiver, and the higher the wall partition, the greater the attenuation achieved.
- The screen should be able to withstand the chemicals and cleaning agents used.
In practice, our experience is that a screen's attenuation rarely exceeds 15 dB. We can pre-calculate how
much attenuation our wall partitions will provide.
You are also welcome to contact us if you want to know more about wall partition
Wall partition set in a hexagon, used as a meeting room.
Wall partition for noise reduction at factories.
What is acoustic regulation?
Acoustic baffles in industry.
Many of our customers are schools.
Acoustic wall inside the machine enclosure.
Acoustic wall inside the machine enclosure.
Noise from a machine consists of the directly radiated sound and the sound reflected from the surfaces of the room.
If the distance from the machine (noise source) increases, the directly radiated noise decreases, but the reflected sound is constant everywhere.
The reflected sound will attenuate only if the surfaces of the room are covered with sound-absorbing material.
In general, a sound measurement cannot distinguish between the contributions of the direct and the reflected sound, so they are registered as one.
Especially the reflected noise is annoying, even at low noise levels.
Therefore, we recommend that you use acoustic regulation as part of your work with noise.
The sound-absorbing properties of a room can be characterised by reverberation time.
When a sound source is suddenly interrupted in a room, it takes some time for the sound to die out due to reflections.
The time it takes for the sound level to decrease 60 dB is called the reverberation time.
Measurement of reverberation time is defined in ISO 3382
ISO 3382 recommends using 2 source positions and 3-4 microphone positions.
In practice, however, reverberation times can often be calculated if the reflecting surface and its area are known.
Contact us if you want to know more about these calculations.
The absorption coefficient is a measure of the sound energy absorbed by a given surface in relation to the energy hitting the surface.
The absorption coefficient depends on the frequency of the sound, and is usually stated by the manufacturer. The higher the frequency, the higher the absorption.
You can find the Danish Working Environment Authority’s requirements and guidance on acoustics here
However, you are also welcome to contact us if you want to know more.
Use of absorbing material.
Installing a qualified amount of high-quality absorbers on the hall’s ceilings and walls has been shown to
reduce noise by 3-5 dB, which is close to halving the amount of noise that damages the ears.
As a rule of thumb, we recommend that 80% of the absorbers be placed on the ceiling and 20% be placed
on the walls, at hearing height approximately 150 cm from the floor.
The installation of absorbing material brings a number of other benefits:
- The improvement will benefit everyone working in the hall. The room becomes significantly less annoying to be in.
- Ceiling absorbers are a prerequisite for wall partitions to work well.
When choosing the type of absorber, there are several requirements that should be met:
- High absorption in the whole frequency range (thick and open surface)
- Do not allow dust or fibres to fall (The surface is treated by the manufacturer, without loss of absorption)
- Do not shade from light (If necessary, lower light fixtures)
- Use Baffles and Clouds if space is limited (Especially for ceilings)
- Do not repaint (Removes open surface and thus reduces absorption)
- Acoustics on walls should be able to withstand a certain degree of impact and shock (Robust)
- Hygiene absorbers should be used in food and pharmaceutical industries
Contact us if you want to know more about the acoustic regulation of rooms. It is non-binding.
What is sound insulation?
Sound insulation is about reducing direct noise, for example, by means of a wall.
When describing how good a wall (or anything else) is at reducing direct noise, the reduction factor R, measured in dB, is used.
A high number means that the sound is strongly attenuated when it passes through the wall (or or anything else)
The reduction factor usually varies greatly with frequency.
When assessing sound insulation properties, it is, therefore, necessary to know the frequency content of the sound to be attenuated.
The reduction factors in the different frequency bands can be added together to form a single number, the weighted reduction factor, known as RW, and it is suitable for speech and noise, which generally have a broad frequency spectrum.
More narrowband noise should be assessed from R in the respective frequency band.
When evaluating the R and RW values, note that they are measured under laboratory conditions.
Thus, our rule of thumb is that the real reductions are some dB lower:
- For R above 60 dB, 6 dB should be subtracted
- For R between 50-59 dB, 5 dB should be subtracted
- For R between 40-49 dB, 4 dB should be subtracted
Noise can be transmitted through many pathways, in addition to walls, such as doors, windows, leaks, installations, etc.
Sound through walls
For the simple wall consisting of solid board, the insulation is determined by the weight of the board per area and by the frequency. Theoretically, R increases by 6 dB each time the frequency is doubled or each time the board weight is doubled.
R is significantly improved if a double board wall is used and even more with an absorber between the plates.
Our MATADOR walls are optimal for soundproofing as:
- It is a double plate steel wall
- It is made of steel, thus heavy
- it has a heavy absorber between the boards
- Standard takes up only 60 mm
- Standard has RW 44 dB
- Can be customised to any desired RW
Sound through doors and windows
Sound insulating doors and windows are available in 6 categories 25, 30, 35, 40, 45 and 50 dB. They can be expected to have an RW of at least the rating minus 3 dB when fitted according to the manufacturer’s instructions. It is important that seals between the wall and the frame are done carefully.
A great sound insulation of windows can be achieved through so-called sound windows, which consist of a double layer of glass, where the 2 glasses have different thicknesses.
Our MATATOR windows and windows in doors are characterised by the fact that they can be adapted to all of the above 6 categories.
Openings, such as holes and gaps, can significantly reduce sound insulation.
Holes in the wall may be necessary for transport systems, ventilation, running of pipes and the like. The holes should therefore be equipped with sound sluices or sealed in other ways.
At Skov Industri, we have 35 years of experience in making these seals and sound sluices.
The reduction factor for a composite surface
A wall, for example, in a machine enclosure, must typically be provided with windows and doors, ventilation and much more. This will usually result in a lower noise insulation than the wall itself.
If you know the area conditions and the RW of the individual elements, it is possible to calculate the total RW of a composite cabin, and of course, we take this into account when we give our noise guarantee.
Requirements for airborne sound insulation
The requirement for airborne sound insulation of a separation between a noisy and non-noisy area should at least ensure that the noise level applicable to the company can be complied with.
If you have any questions about sound insulation, please feel free to contact us. It is non-binding.
Quiet break room.
Soundproof meeting room in the pharmaceutical industry.
Control panels inserted into the Matador wall.
When the ventilation is noisy
Heating and ventilation systems, compressed air, water, waste transport, etc. are examples of fixed building installations. Here we will look at the most dominant in relation to noise, the ventilation system.
Noise from ventilation systems can occur at many points in the plant. However, fans are often a dominant source of noise and the noise generated depends very much on the fan type.
Usually radial fans are less noisy than axial fans.
Inlet and outlet fittings should be as noise-reducing as possible, as they are challenging to attenuate afterwards.
The channel-transmitting noise can be attenuated via many variants of standard mufflers.
If you have any questions about Soundproofing of ventilation, please feel free to contact us. It is non-binding.
A machine can be sound proofed from the inside
Intervention can be made in various places inside a machine when it needs to be noise attenuated.
Relatively simple measurements can help pinpoint where the noise is coming from.
It is the responsibility of the supplier of the machinery to ensure that it is adequately soundproofed from the inside.
There are many rules and methods for this work, too extensive to cover here.
But you are always welcome to contact us if you want to know more.
Diesel engine seen from inside.
When vibrations cause problems
2 machine enclosures with access via doors and gates.
Floor to ceiling machine enclosure.
Soundproofed supervisor office.
Vibrations from machinery can propagate through floors and other building parts and can cause nuisance even in remote buildings.
So-called vibration insulation may therefore be a necessary condition to avoid noise problems in neighbouring buildings.
The right insulators can usually be selected based on simple assessments.
Basically, there must be no fixed connection that can transmit sound from the machine to the environment.
If production premises are located close to canteens, offices or other noise-sensitive areas, you should pay extra attention to vibration insulation.
In other cases, for example, very large machines can even cause walls and floors to crack.
Even small vibrations in buildings can interfere with precision work, such as accurate scales and other measuring equipment.
However, transmission to the floor can sometimes be so violent that it is directly annoying to the persons operating the machine.
Vibration insulation is achieved by installing resilient elements between the machine and the building to inhibit vibration transmission.
In practice, vibration insulation is achieved by mounting the machine on vibration insulators, i.e. spring elements, usually made of rubber or steel.
When setting up machines on insulators:
- Assess the stability of the floor/surface and determine the optimum position of the machine on the floor/surface. An independent foundation may be necessary.
- Some machines can be placed on a frame construction.
- The total weight and the location of the centre of gravity are determined for the machine and possibly the frame. The weight on each support point should be evenly distributed across the support points.
- The frequency of the machine vibrations is determined.
- The degree of insulation is determined for the installation.
- Suitable insulators are selected.
- Shafts, cable transfers, etc. are made elastically.
Contact us if you want to know more about vibration damping.
Enclosure of machinery, production equipment and robots
Enclosure is generally an effective method of noise reduction. You can enclose parts of a machine, or the whole machine.
Our MATADOR enclosures can deliver sound attenuation up to 50 dB, perhaps the best market.
Enclosing machinery requires thorough preparation. All too often, poor preparation is the reason why noise reduction is not optimal.
The main challenge is the openings that the enclosure must have for the inflow and outflow of materials.
We have 35 years of experience and have enclosed over 1,000 machines, production plants and robots, in virtually all industries. See more here
Or contact us if you want to know more about enclosures.
About wearing hearing protection
You are REQUIRED to wear hearing protection if the noise is above 85 dB(A).
Hearing protection is an emergency solution that should only be used where it is not possible to sufficiently attenuate the noise.
Hearing protection must ensure sufficient attenuation while causing the least possible nuisance.
Just as there is a big difference in how prone we are to sunburn, there is a big difference in the hearing damage we get from a given noise. Some can tolerate 90 dB for years, while others can barely tolerate 80 dB.
The Danish Working Environment Authority recommends using hearing protection if the noise is above 80 dB(A) and you MUST use hearing protection at 85 dB(A) See more here
Contact us if you want to know more about hearing protection.
Noise is unhealthy
Many studies and surveys suggest that noise is harmful, not only to the ears.
The Danish Working Environment Authority puts it this way:
“Loud noise can damage hearing
Hearing damage usually creeps up on one. It can be difficult to detect that your hearing is deteriorating because you compensate by turning up the radio, for example.
Signs of hearing loss are:
- That you think other people are mumbling
- That it is difficult to have a conversation when there is background noise in the room – for example at parties
- That you often have to ask for things to be repeated
- That it is necessary to turn up the TV and radio.
Hearing can be damaged after a single exposure to thunderous noise, such as a gunshot or an explosion. However, long-term daily exposure can also often cause gradual hearing damage.
Hearing damage develops fastest in the first years of exposure, typically when you are young. Hearing also deteriorates with age. Hearing loss is not curable and is the most common incurable occupational disease according to the World Health Organization (WHO)."
If you want to know more about the impact of noise, please contact us.
Many schools and daycare centres are our customers.
Hearing protection is only a temporary solution.
Acoustic baffles in industry.
Matador Acoustic wall inside the machine enclosure.
Acoustic wall in an institution.
Here we have collected a number of basic concepts used in the work with noise and acoustics.
- Noise – is harmful or annoying sound.
- Sound – is pressure waves moving through air, or elastic material. Alternating positive and negative pressure moves forward and the pressure variation eventually hits our ear
- Sound – is measured in decibels (dB) and is a measure of pressure variation
- dB is a relative quantity like % and follows a Logarithmic scale
- dB 0 corresponds to a pressure variation of 20 μPa corresponding to what we can just about hear.
- dB 140 corresponds to a pressure variation of 200,000,000 μPa corresponding to the pain threshold
- Sound pressure, sound power and sound intensity are all measured in dB, but are not the same
- Halving of sound pressure is equivalent to 6 dB (Damage to the ear)
- Halving the sound power (energy) is equivalent to 3 dB (Damage to things other than the ear)
- Halving of perceived loudness is equivalent to about 10 dB
- The energy equivalent sound pressure level is denoted Leq and corresponds to the sound pressure impact over time.
- Leq8 hours is thus the sound pressure level for a working day
- dB(A) is the average sound pressure level over a full working day, i.e. 8 hours
- Frequency is an expression of how fast the sound pressure fluctuates – how many oscillations there are per second.
- Frequency is measured in Hertz, abbreviated Hz
- The human ear can perceive from 20 Hz up to 18,000 Hz (18kHz) (However, if the sound is loud enough, sounds below 20 Hz can be heard)
- The ear is most sensitive in the range 1,000 Hz to 4,000 Hz (1kHz to 4kHz)
- For workplace measurements, a filter is used so that the measurement reflects the sensitivity of the ear to different frequencies and is denoted as dB(A)
- The Danish Working Environment Authority requires noise to be attenuated if the noise exceeds 85 dB(A) and thus expresses a weighted noise level.
- Sound energy, sound power, and sound intensity is the energy in Watt emitted by a sound source (machine) per unit of time
- The sound energy is the energy of the sound waves. The bigger the waves (lower frequency), the more energy the waves contain.
Contact us if you have any questions about the basic concepts or noise measurements. It is non-binding.
What is the legislation – inside and outside?
Legislation on noise can be divided into 2 main areas
- Noise to the surroundings of the company
- Noise at work
Noise at work
Noise in the workplace is legally regulated first and foremost by the Danish Working Environment
The following should be noted:
- No one should be exposed to noise levels exceeding 85 dB(A) or peaks of pulses exceeding 137 dB(C).
- The employer is responsible for ensuring that all noise is abated where possible and financially possible.
- Hearing protection is a temporary solution.
- The employee is obliged to wear hearing protection if the noise is above 85 dB(A).
- The employer must provide hearing protectors for employees if the noise level exceeds 80 dB(A), or the peak levels exceed 135 dB(C), or the noise is otherwise harmful or very annoying. This may be the case, for example, if work is carried out for a short time in very noisy conditions.
We recommend that you read this WEA guide D 6.1-5
Limits for external noise from companies
External noise from the company is regulated by the Environmental Act and we recommend that you read
The limits for environmental noise are given below: (Source: Environmental Law)
The limit values are primarily used in connection with environmental permits and orders, but can also be used in planning. There are different indicative limit values for the daytime, evening and night-time periods.
Please contact us if you know more about legislation on noise
Soundproofed supervisor office.
9-metre high Matador wall shields against both noise and heat from production facilities.
4×3 m door, so new machines can enter.
We hope you learned more about noise reduction and acoustics?
We are your noise reduction specialist.
We hope that our learning centre has made you more aware of noise reduction and acoustics.
If you have ideas on how to improve our learning centre, we'd love to hear from you.
If you need any further information or have any questions, please feel free to contact us.
- AWEA guides on noise and acoustics
- Various published articles on noise and the harm of noise.
- Various basic books on noise reduction, including Basic Book on Noise Reduction – Service Center of the Danish Work Environment Council 1999
- And not least our experience in noise reduction over 35 years