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Noise mitigation endeavors frequently demand the assessment of diverse acoustic parameters in order to evaluate the efficiency of their noise reduction process.

The assessment of noise levels is essential indeed to establish adherence to noise-related regulations.

Noise evaluations might be necessary for diagnostic intentions or to pinpoint the origin (or origins) of sound within a machinery component.

Acoustic measurements can also be utilized to discern the routes taken by noise transmission within a system.

The article briefly introduces the main noise measurement instruments for industrial noise control environment.

Which acoustic measurement equipment is required?

Everything begins with the accurate selection of measurement instrument to monitor and measure sound properties.

When we have a basic scenario that needs assessing the severity of environmental noise, it might be sufficient to measure either the overall sound pressure level or the A-weighted level, employing a basic sound level meter. For instance, if the aim is to measure whether the sound level within a room surpasses 90 dBA, then utilizing a portable or hand-held sound level meter would be appropriate.

There are instances where a more comprehensive assessment of the noise is required instead.

In such situations, measurements involving octave band or 1/3 octave band sound levels may be conducted.

To conduct these measurements, a sound level meter furnished with octave band or 1/3 octave band filters is essential.

Alternatively, an acoustic spectrum analyzer that employs microprocessors to manipulate input data could be a recommended choice.

To ensure adherence to noise exposure regulations, dosi-meters can be employed to measure and record accumulated noise exposure.

Data on the sound power generated by machinery and equipment is crucial for creating more subdued mechanical systems, conducting acoustic evaluations among various machines, and identify key information concerning production machinery and equipment.

Noise measurement: main parameters

Measurement techniques play a crucial role in assessing noise properties and their impact on the environment, personnel health, and various applications. Several key parameters need to be fulfilled by these techniques to provide a holistic assessment of noise properties.

An article recently published by Occupational Health and Safety Blog identified six of them: (1) Sound Pressure Level (SPL); (2) frequency; (3) duration; (4) noise dose; (5) peak levels; (6) weighting.

Three of such parameters should be always measured in industrial noise control:

• Constitutes the fundamental measure of sound magnitude, which is normally expressed in decibels (dB). In this case, the measurement instrument captures the fluctuations in air pressure induced by sound waves in relation to ambient atmospheric pressure.
• Is about the frequency of sound wave cycles per second, which is normally quantified in hertz (Hz). Varied sounds exhibit diverse frequencies, prompting a comprehensive analysis of sound across its frequency spectrum.
• Accounts for the temporal extent of sound. This aspect gains relevance while assessing prolonged noise exposure, particularly in occupational scenarios.

Sound level meter (SLM): one of the most widely used acoustic measurement instruments

Sound level meters are special equipment composed of a microphone, amplifiers, weighting networks, and a display indicating decibels.

The microphone acts to convert the input acoustic signal (acoustic pressure) into an electrical signal (usually voltage). This signal is magnified as it passes through the electronic pre-amplifier.

The amplified signal may then be modified by the weighting network to obtain the A-, B-, or C-weighted signal. This signal is digitized to drive the display meter, where the output is indicated in decibels. The display setting may be ‘‘fast’’ response, ‘‘slow’’ response, ‘‘impact’’ response, or ‘‘peak’’ response. Unless one is interested in measuring rapid noise fluctuations, the ‘‘slow’’ response setting is usually used.

An output jack may be provided to record or analyze the signal in an external instrument system. Sound level meters are rated in the following categories, based on the accuracy of the meter:

(a) type 1, precision;

(b) type 2, general-purpose;

(c) type 3, survey;

(d) special-purpose sound level meters.

There are several items of auxiliary equipment that are used with sound level meters, including a calibrator and a windscreen.

Many sound level meters have output ports for connection to a PC for post-processing of data.

Measurement services by Stopson Italiana

Stopson Italiana conducts measurements in accordance with main regulation on force. We can conduct various types of measurements, notably:

• Acoustic measurements of the impact on neighbouring communities (temporal evolution in dBA, Leq measurement, 1/3 octave spectrum analysis) from 1.5m to 7m above ground level;
• Acoustic impact measurements at property fence;
• Residual noise acoustic measurements;
• Exploratory acoustic measurements (acoustic research and characterization of sound sources, calculation of sound power levels emitted).

⟶ To Discover all the Site Services offered by Stopson Italiana click HERE.

One of the first stages for designing a soundproofing strategy? Finding the right acoustic requirements.

Different “failure criteria” exist for various scenarios. And just like mechanical design, acoustic design encompasses diverse criteria for different applications.

Some designs aim to reduce noise that hinders workers’ communication or their ability to perform assigned tasks. In other cases, the goal is to avoid negative reactions from the surrounding communities near a noisy plant.

In this article, we focus on how acoustic designers should seek to reduce noise to a level that doesn’t prevent permanent hearing loss among industrial workers.

The human ear and hearing loss risks

In order to comprehend the detrimental impact of sound on the human ear, it is necessary to briefly grasp the anatomical structure of the ear.

The human ear is an extraordinary auditory system. It can perceive sounds within a frequency spectrum ranging from approximately 16 to 20 Hz up to frequencies in the 16 to 20 kHz range.

Furthermore, the ear has the capacity to detect acoustic pressures as low as 20 mPa at a frequency of 1000 Hz and endure acoustic pressures as high as 2000 mPa for brief durations.

Due to the acoustic characteristics of the outer ear and the mechanical features of the middle ear, the human ear does not act as a linear transducer for sound pressure levels.

At the same time, due to the poor acoustic impedance matching between the air outside the ear and the outer ear at frequencies below about 500 Hz, the ear can detect only sounds that have a pressure level greater than about 12 dB for frequencies of 250 Hz and lower.

For a sound pressure level of approximately 120 dB with a frequency between 500 Hz and 10 kHz, an individual will experience a tickling sensation in the ears. This level represents the threshold of ‘‘feeling’’ or the beginning of discomfort due to noise.

When the sound pressure level is increased above approximately 140 dB, the threshold of pain is reached. Continuous exposure to noise above 140 dB for a few minutes can result in permanent damage to the ears.

Industrial noise criteria and exposure standards: a model from the United States

Therefore, one of the primary reasons for implementing soundproofing solutions today is to safeguard workers from hearing loss caused by occupational noise exposure.

In the United States, the government has implemented several frameworks to assist in establishing acoustic parameters that define acceptable noise levels.

In 1965, the National Academy of Sciences and the National Research Council’s Committee on Hearing, Bioacoustics, and Biomechanics (CHABA) developed noise exposure criteria, according to which acceptable noise level should not result in a permanent threshold shift (NIPTS) exceeding 10 dB at 1 kHz and below, 15 dB at 2 kHz, and 20 dB at 3 kHz or higher after 10 or more years of exposure.

In 1970, the Occupational Safety and Health Administration (OSHA) established a noise exposure limit of 90 dBA for an 8-hour workday, allowing higher noise exposures for shorter durations. For every 5 dBA increase above 90 dBA, the permissible exposure time was reduced.

Moreover, according to OSHA’s criteria, exposure to noise levels exceeding 115 dBA is not allowed for any duration. The action level, which triggers the initiation of hearing conservation measures, was set at 85 dBA. The upper limit for impulsive noise exposure was established at 140 dBA.

Soundproofing measures

If the noise level surpasses the permissible limits set by governmental criteria, the employer must take necessary steps.

Firstly, a noise survey should be conducted to identify areas where limits are exceeded and determine the specific source of noise.

Secondly, engineering measures or controls should be implemented to reduce worker exposure to noise.

Some examples of engineering control measures:

• Substituting machinery with quieter options: this can involve using larger, slower machines, employing belt drives instead of gear drives, or redesigning the equipment to emit lower levels of noise.
• Substituting manufacturing processes: switching to quieter alternatives, such as using welding instead of riveting, can help reduce noise emissions.
• Replacing worn or loose parts: worn-out or loosely fitting components should be replaced to minimize noise generation.
• Installing vibration dampers and isolators: these measures help reduce the transmission of vibrations and subsequently lower noise levels.
• Installing flexible mountings and connectors: using flexible materials for mounting and connecting equipment can help to absorb vibrations and reduce noise propagation.
• Enclosing the noise source: placing the noise source within an enclosure or employing acoustic barriers between the worker and the noise source can help contain and diminish noise levels.
• Isolating the worker from the noise source: creating an acoustically treated room where the worker and machine controls are situated can effectively isolate the worker from the noise source.

By implementing these engineering control measures, employers can mitigate excessive noise levels and minimize the risk of hearing damage to their workers.

As well as implementing engineering control measures, employers can adopt Industrial Silencers to perform acoustic attenuation.

⟶ To Discover all the Silencers offered by Stopson Italiana click HERE.

Noise-induced effects pose significant concerns for individuals employed in the industrial sector and not only.

Numerous manufacturing facilities look to adopt industrial silencers with a view to mitigate risks through acoustic attenuation. The final goal is to safeguard the surrounding from the harmful consequences of loud machinery and noisy production areas. 

Industrial silencers find application in managing noise levels associated with diverse industrial processes. However, the selection of a silencer that fits perfectly your needs is anything but an easy task.

Silencer manufacturers may offer many possibilities, and for this reason, an expert guide is necessary to accurately evaluate the technical needs of your plants and so make the right choice.

First things to take into account

While selecting industrial silencers, it is essential to consider three main factors: physical specifications, performance specifications, and mounting attachments.

• By physical specifications, we refer to the size of the inlet and outlet, which can differ from round, circular, or oval-shaped cross sections to square or rectangular shapes.
• Performance specifications include noise attenuation, maximum pressure rating, and maximum flow rating.
• Mounting attachments may include male threads, female threads, flanges, and pipe clamps.

Main applications of Industrial Silencers

Industrial silencers have a wide range of applications. Most silencers available on the market are purpose-built to diminish noise produced by specific industrial pieces of equipment, like engines, air or gas compressors, vacuum pumps, or turbines.

Major categories of silencers according to their common application field:

• Vent/Blowdown Silencer: these silencers are designed for rapid exhaust or venting applications, commonly known as “blow off” silencers.
• Compressor Silencer: usually tailor-made for air or gas compressors to minimize noise generated during their operation.
• Blower/Fan Silencer: designed specifically for the intake or outlet of fans or blowers. These silencers may incorporate features like air filters and other enhancements.
• Pressure Relief Valve Silencer: developed for use with backpressure or pressure relief valves to attenuate noise associated with relief blow-offs.
• Turbine Silencer: intended for noise reduction at the inlet and/or outlet ports of turbines, typically applied to gas turbines.
• Vacuum Pump Silencer: specifically designed to reduce noise at the inlet and/or outlet of vacuum pumps.
• Engine Silencer: utilized to reduce noise from industrial engines. Both inlet and outlet silencers can be used.
• Chimney Silencer: designed to mitigate noise from combustion exhaust systems, commonly found in industrial boilers, ovens, and furnaces.

The design features every Silencer should follow

When selecting an industrial silencer, it is essential to carefully consider various technical features to ensure that the equipment aligns perfectly with your plant’s requirements.

• Acoustic features: the silencer should consistently deliver the desired level of sound power reduction across different frequency ranges; this quality is measured by Dynamic Insertion Loss (DIL). It is important to note that the acoustical performance of a silencer can be influenced by factors like temperature, gas characteristics, system configuration, and physical layout of the operating environment.
• Geometrical features: the silencer needs to be appropriately sized and shaped to fit within the available space.
• Mechanical features: the silencer should require minimal maintenance and provide high efficiency over extended periods. Additionally, its design should incorporate durable materials capable of withstanding elevated temperatures and potentially corrosive gasses.
• Aerodynamic features: airflow passing through the silencer will cause a pressure loss, which can impact its acoustic performance. Therefore, the design should take into account the dynamics of airflow.
• Economic features: it is crucial to consider the overall cost-effectiveness of the silencer, taking into account factors such as initial investment, operational efficiency, and maintenance requirements.

Types of Silencers by Stopson Italiana

Stopson Italiana’s Industrial Silencers are designed to handle both cold and hot gasses.

Our Silencers are of absorptive type for exhaust systems of engines or small boilers and incorporate reactive properties as well. Additionally, they have a combination of absorptive and reactive features for venting systems.

Our Silencers are available in circular or rectangular shapes and can be used in atmospheric or pressurized conditions with various gasses, temperature ranges, and applications. They can provide sound attenuation of up to 70 dB, effectively reducing residual noise to a sustainable level.

Our offering mainly includes:

• Vent Silencers, which are engineered to minimize the noise generated by exhaust piping that release pressurized gaseous fluids such as air, vapor, natural gas, nitrogen, oxygen, carbon dioxide, and more into the atmosphere.
• Engine Exhaust Silencers, which are conceived to be used on diesel and gas engines, as well as on industrial low/middle power gas turbines.
• Intake & Stack Silencers, which reduce noise emissions in air filtration systems, inlet ducts, ventilation systems, by-pass stacks and exhaust ducts.
• Ventilation & Duck Silencers, designed to reduce noise level through the duct generated by any sound source, such as fans, conditioning units, etc.
• In-line Silencers, pressurized equipment which are built to reduce the noise generated by valves or compressors.

⟶ To Discover more about the range of Silencers offered by Stopson Italiana click HERE.

The increasing demand for machinery and components with certified sound levels has led many companies to recognize the importance of having a controlled sound environment for conducting measurements. 

Nevertheless, traditional masonry rooms are not always cost-effective or flexible enough to meet these specific industrial requirements. 

Therefore, alternative solutions are being considered to better adapt to installation development and provide flexibility.

Typical applications of Anechoic and Hemi-anechoic Chambers

Anechoic chambers are targeted for various industries that require precise acoustic testing and analysis. Industries that commonly employ anechoic and hemi-anechoic chambers include:

• Companies producing noise-generating devices or pieces of equipment. For instance, they are extensively used in the automotive sector for testing vehicle components, such as engines, exhaust systems, and vehicle interiors, to assess their noise levels, vibration characteristics, and acoustic performances. As a matter of fact, any vehicle manufacturer should perform a rigorous testing to ensure compliance with national planning standards before releasing a new model into a market.
• Companies producing noise control products and testing facilities, as well as any organization responsible for ensuring that their services meet requirements, thereby establishing tightly regulated acoustic environments.

Designing Anechoic and Hemi-anechoic Chambers

Creating an insulated test environment is essential in the first place for precise noise analysis. 

Chambers can be either of an anechoic chamber or hemi-anechoic design pattern. What is the main difference?

• Anechoic chambers are designed with sound-absorbent materials on all six sides, effectively eliminating external noise and controlling frequency cut-off. 
• Hemi-anechoic chambers, on the other hand, have a solid floor with anechoic wedges on five sides, allowing examination of how noise interacts with real-world surfaces.

Anechoic and hemi-anechoic chambers are typically tailored to specific testing needs and frequency requirements, often aligned with ISO standards. 

The size of these chambers is primarily dictated by the equipment under test. Their sizes can range from extremely large ones used for instance in the case of automotive testing, to very small chambers, employed to test more compact devices.

Main benefits of Anechoic and Hemi-anechoic Chambers

As stated earlier, these chambers are instrumental to facilitate the development and testing of any noise-generating products. 

Another example of an industrial sector that has been significantly affected is the aerospace industry.  These chambers are particularly used in the fields of research and development to test aircraft engines, jet noise reduction technologies, aircraft interiors, and other aerospace components for noise emissions and acoustic characteristics.

In short, they give significant assistance in identifying unexpected noises and vibration issues that may arise during operations. For instance, many types of industrial machinery can be tested in a hemi-anechoic chamber to assess their vibration properties.

However, benefits are not just limited to sound isolation.

Anechoic and Hemi-anechoic chambers also provide total protection against electromagnetic interference, such as radio waves, which could disrupt the product or sensitive measuring instruments.

More importantly, unlike any other soundproofing chambers, which attenuate noise levels to around 10-20 dBA, Anechoic and Hemi-anechoic chambers can be designed to achieve even lower levels, reaching as little as -20 dBA if required.

Anechoic and Hemi-anechoic Chambers by Stopson Italiana

Stopson Italiana offers a range of prefabricated Anechoic or Hemi-anechoic Chambers that are internally treated with standard wedges, according to the lowest operating frequency. Our products are tailored for professional testing in various fields.

Our case history includes the implementation of a hemi-anechoic chamber for acoustic testing in a Home Appliances Plant, in Pordenone, Italy. The chamber in question was provided with a modular construction for easy dismantling and built with non-combustible sound absorbing materials.

Stopson Italiana’s anechoic chambers can also be optionally equipped with a control room. Such a setup provides working areas with sufficiently low sound pressure levels, limited reverberation, and ensures accurate acoustic performance.

Our anechoic chambers typically have a cut-off frequency of 125Hz and can be equipped with various features depending on their intended use. These features may include suitable interior lighting, exhaust gas extraction systems, independent ventilation and cooling systems, air-conditioned aspiration/exhaust, easy access to tested devices, safety glass for visual inspection during testing, and long-lasting soundproofing materials.

⟶ To Discover more Test Facilities Solutions offered by Stopson Italiana click HERE.

Soundproofing approaches are critical measures to prevent harmful sound waves from permeating within industrial setting. However, choosing the appropriate strategies depends on different types of noise, essential factors to be considered while designing a safe and efficient industrial workspace.

In this regard, diving into the physics of sound and the relative methods to abate noise levels in industrial settings can be beneficial while selecting the most suitable solution for specific noise-related exigencies.

Types of noise and relative approaches

The noise industrial facility managers and industrial engineers should be concerned about can be divided into three main categories, depending on the means of transmittance: airborne noise, solid-born noise, and impact noise. Each of them requires a tailored approach to mitigation.

Airborne noise is primarily caused to the vibration of the air. More specifically, it refers to sound waves travelling through the air. In this case, the reduction strategy should be drawn on the application of materials that absorb the aforesaid sound waves, such as acoustic panels and soundproofing curtains. These are commonly known as “heat-insulating materials”, since they minimize the noise that is transmitted through the air by literally converting the sound energy into heat energy.

Solid-borne noise, on the other hand, is primarily due to the impact of solids or solid vibrations. The reduction strategy here must take into account the fact that the sound permeates walls, floors, and ceilings with ease. Accordingly, the application of specific vibration isolations materials, such as rubber mats or spring, will be required to absorb or isolate the vibration prior to being transmitted through the structure.

Impact noise, lastly, is produced by physical impacts, including footsteps and machinery vibrations. Similarly to what occurs in solid-borne noise circumstances, the best noise eradication execution can be achieved here by applying materials that absorb impact, such as thick carpets or rubber mats.

It should be also noted that sound permeation is strictly tied to “mass law”: the effectiveness of a wall or plate’s soundproofing performance largely depends on how much mass it has in relation to its area. When it comes to selecting sound insulation materials, the higher the mass, the more difficult it is to make it vibrate. Opting for a dense and heavy material is hence, in most of the cases, the best option.

The effectiveness of soundproofing approaches can still vary depending on the frequency and intensity of the noise. Ultimately, a combination of soundproofing materials and techniques may be recommended to effectively reduce noise level and attain sound transmission loss.

The importance of partnering with a specialized soundproofing company

Relying on industrial noise control manufacturer may be game-changing to identify the best materials and techniques to soundproof your industrial setting and fulfill noise mitigation challenges.

Stopson Italiana, which counts on a proven reference list of partners from a variety of industries, certifies an extensive knowledge in providing industrial noise control solution on a global level.

Following an initial consultation path, a team of experts will provide support to identify the source of noise and its type, select the most appropriate soundproofing materials according to its properties, and eventually deliver the solutions that best fit your case. Stopson Italiana offers acoustic panels, sound barriers and vibration isolation materials among them.