Stopson Turkiye acquires a new key accreditation with the ASME Certificate for U-Stamp

Stopson Turkiye makes the first step towards the highest manufacturing performance for unfired pressure vessels: ASME Certificate for U-Stamp achieved!

An introduction to U-Stamp and ASME Certificate

U-Stamp is the official acknowledgement that an unfired pressure vessel is designed, manufactured and controlled in accordance with ASME VIII Div.1 Rules.

ASME Codes are the most famous international references for manufacturing of pressure retaining equipment that allow the installation of safe equipment, available to resist for all its life cycle to any design and process condition, with safety margin avoiding undesired failures.

U-Stamp is also the fundamental requirement that any pressure retaining equipment needs to have in order to be installed in North America.

This achievement thus certifies the capability of Stopson Turkiye to deliver silencers manufactured according to the highest standard and that can be installed all over the world, in any plant and at any condition.

The process

ASME Certificate of Stopson Turkiye means that any silencer which needs a U-Stamp Robust mechanical and structural analysis from qualified Engineering Team

  • Efficient and well-oiled internal management process
  • Highest quality check on raw material
  • Detailed check on all manufacturing activity under supervision of qualified QC Department 
  • Review of engineering and manufacturing procedure by ASME qualified consultant agency

Personnel and processes involved in manufacturing of silencers according to ASME VIII Div.1 are constantly trained and informed in case of any latest release of the Codes, or of internal QC Manual.

Year after year our team and our organization will be certified, confirming top level processes and ensuring to all our customers the guarantee of top ranked products.

The team

The certification process commenced early December 2023 and, with support of ASME Authorized Inspection Agency, led to conclusion in just 3 months thanks to the close and productive cooperation of an amazing Team:
  • Technical Manager: Olgay Yıldırım
  • Design Manager: Luca Fenini
  • Quality Team Leader: Umut Güven
  • Quality Assurance Engineer: Ayşe Turgut
  • III Level Inspector: Ekim Tepe

Thanks to the amazing team for achieving this milestone!

In-Line Silencers by Stopson Italiana

In-Line Silencers are a type of Silencers designed to mitigate the noise produced by valves or compressors

These silencers, characterized by their exclusive design and manufacturing, require in-depth engineering expertise, field experience, and meticulous quality processes to ensure the delivery of high-performing and safe products.

In-Line silencers are adept at reducing the noise emitted by control valves or compressors within pipelines

By strategically integrating In-Line Silencers into the piping system, noise levels can be effectively diminished. 

If interested in learning more about Stopson Italiana’s In-Line Silencers, including details about specialized materials, testing procedures, and the engineering process, click HERE.

Insights into Noise Pollution

Excessive noise, commonly referred to as noise pollution, poses a significant threat to human well-being globally. It primarily stems from atmospheric, environmental, and occupational sources, including industrial machinery and indoor equipment.

Industrial workers often face hazardous noise levels, endangering their health. Despite regulations in many countries aimed at reducing noise hazards, enforcement remains inconsistent, resulting in variations in noise laws and ordinances worldwide.

In order to comprehend the intricacies of industrial noise, and consequently, the techniques employed for soundproofing, it is imperative to embark on an exploration of sound and noise pollution.


Introduction: Classes of noise and noise pollution 

As already discussed in previous publications, noise pollution is the disturbing noise that can harm human well-being, and it has become a significant concern in today’s industrial environments.

Noise is pervasive, with some industrial areas experiencing particularly loud continuous noise. Physically, there’s no difference between sound and noise; noise refers to undesired sound and any unnecessary disturbance within a useful frequency band.

Generally speaking, most outdoor and environmental noise is caused by industrial machines, transportation systems, and indoor activities such as machinery in workplaces, building activities, household appliances, and music performances.

Noise is also defined as unwanted sound and a form of energy emitted by a vibrating body, which, upon reaching the human ear, creates the sensation of hearing through nerves. Not all sounds produced by vibrating bodies are audible; the audible range is typically between 20 Hz to 20 kHz. Frequencies below 20 Hz are called infrasonics, and those above 20 kHz are termed ultrasonics.

Noise can be continuous or intermittent, and it may be of high or low frequency, both of which are undesirable for normal human hearing.

The distinction between sound and noise can also depend on the recipient’s inclination and interest, ambient conditions, and the impact of the sound at that moment. Noise intensity is typically measured in logarithmic units (dB) because this scale allows a wide range of pressures to be described without using large numbers and represents the nonlinear behavior of the ear more accurately.

Let’s examine three distinct classes of noise:

  • Atmospheric noise: This type of radio noise arises from natural atmospheric phenomena, primarily lightning discharges during thunderstorms. Worldwide, approximately 3.5 million lightning flashes occur daily, constituting atmospheric noise, with cloud-to-ground flashes being more prevalent. At very low frequencies (VLF) and low frequencies (LF), atmospheric noise tends to dominate, while at high frequencies (HF), man-made noise, especially in urban areas, is more prominent.
  • Environmental noise: Environmental noise encompasses noise pollution from external sources, primarily caused by transportation systems such as buses, trains, cars, aircraft, and recreational activities like sports and music performances. This type of noise is present in various human activities and can have diverse effects on individuals, ranging from emotional to physiological and psychological. While low-level noise may not be harmful, prolonged exposure to environmental noise can lead to annoyance, sleep disturbances, hearing loss, and stress-related problems. Transportation noise originates from engine/exhaust and aerodynamic sources, while recreational noise can come from various activities and processes. Additionally, background noise from alarms, conversations, and bioacoustic sources like animals or birds contributes to environmental noise.
  • Occupational noise: This refers to noise that affects workers during their job duties, either from the work environment or the machinery they operate. Industrial noise varies in intensity, frequency components, and consistency. Some machinery produces continuous noise with a relatively uniform frequency response and consistent level, while others exhibit intermittent periods of higher noise levels amidst lower background noise.

Technical terms and detailed related to noise pollution

The definitions of key technical terms concerning noise pollution measurement parameters and indicators are sourced from the American National Standards Institute (ANSI) standards, ANSI S1.1-1994 or ANSI S3.20-1995, as per the terminology employed in those standards:

  • Audiogram: A graphical representation of hearing threshold levels plotted against frequency. Frequencies below 20 Hz are termed infrasonics, while those above 20,000 Hz are referred to as ultrasonics.
  • Baseline Audiogram: The initial audiogram against which subsequent ones are compared to assess significant threshold shifts. It is obtained from an audiometric examination conducted before or within the first 30 days of employment following at least 12 hours of silence.
  • Continuous Noise: Noise characterized by negligible fluctuations in level during the observation period.
  • Crest Factor: Ten times the base-10 logarithm of the square of the wideband peak amplitude of a signal to the time-mean-square amplitude over a specified time period.
  • Decibel, A-weighted (dBA): The sound level measured using the A-weighting network on a sound level meter.
  • Decibel, C-weighted (dBC): The sound level measured using the C-weighting network on a sound level meter.
  • Noise Reduction Rating (NRR): An indicator of a hearing protector’s noise reduction capabilities, expressed in decibels (dB). It is a single-number rating required by law to be displayed on the label of each hearing protector sold in the USA.
  • Derate: The process of using a fraction of a hearing protector’s NRR to calculate the noise exposure of a worker wearing that protector.

The Effects of noise pollution on human health

Noise pollution has significant societal costs, prompting commitments from organizations like the European Commission (EC) and the World Health Organization (WHO) to stringent noise reduction targets.

Acute noise exposure triggers the release of stress hormones, such as adrenaline, leading to changes in normal bodily functions. Severe effects can occur even at relatively low environmental noise levels, disrupting concentration, relaxation, or sleep. Night-time noise, in particular, may impact cardiovascular health due to sleep disturbances.

WHO recommends night-time noise levels below 55 dB(A) to prevent adverse health effects in the short term, with a long-term goal of 40 dB(A). Common effects of noise pollution on vulnerable populations include annoyance, sleep disturbance, heart and circulation problems, diminished quality of life, cognitive impairment, and hearing loss. Prolonged exposure to continuous noise levels of 85–90 dB(A) in industrial settings can result in progressive hearing loss, particularly in the frequency range of 3 kHz to 6 kHz. Speech intelligibility can be reduced even at 10 dB, with noticeable social hearing handicaps above 30 dB. The impact of noise on health can vary based on sound characteristics such as intensity, frequency, complexity, and duration.


Industrial soundproofing systems, like those offered by STOPSON ITALIANA, are specifically designed to mitigate the effects of noise pollution in industrial settings. These systems target the type of noise described previously, focusing on reducing noise levels generated by industrial processes and machinery.

By implementing soundproofing solutions from Stopson Italiana, industrial facilities can effectively combat this type of noise, creating a quieter and safer working environment for employees and surrounding communities.

Stopson Italiana extends warm wishes to you and your team for a joyful Christmas and a festive holiday season!

Season’s Greetings from Stopson Italiana!

Reflecting on the concluding year, 2023 has seen us proudly solidify again our position as a distinguished global industry leader. Our comprehensive understanding of soundproofing patterns and engineering practices has been pivotal in our continuous efforts to elevate product performance.

This year marked a significant milestone with the establishment of Stopson Türkiye, born from the merger of Turkish leaders Modcon Makina and Prodinox Metal. Building on a robust relationship since 2016, this strategic partnership unites three companies with complementary expertise, creating a unified entity dedicated to delivering high-quality, reliable products and services globally.

The establishment of Stopson Türkiye represented a significant step forward, combining diverse strengths into a unified entity dedicated to delivering high-quality, reliable products and services to meet the evolving needs of customers worldwide.

At the same time, we expanded our portfolio with numerous successful projects, reinforcing our unwavering international commitment. As in previous years, plants and industrial complexes entrusted us to effectively address and eliminate noise pollution in their production environments.

Looking ahead to 2024, our commitment to innovation remains steadfast as we strive to enhance our offerings and provide customers with the utmost reliability in soundproofing products and services.

We express sincere gratitude to our valued customers, communities, partners, and stakeholders for their unwavering support throughout the year.

Wishing you and your team a Merry Christmas and a Happy New Year!

Acoustic Enclosures: a transformative solution to noise control

Acoustic enclosures are largely implemented in the industry to limit excessive noisiness of machines and installations that are situated outside of production settings and technological equipment. The latter are usually responsible for the acoustic degradation of the environment and personnel’s health.

In this article, we briefly introduce their function for noise control. In particular, we try to determine the influence of materials and constructional solutions on the acoustic effectiveness of enclosures


An enclosure serves as a passive device designed to impose limitations on noise. It often represents the sole viable method for curtailing sound radiation generated by acoustically active machinery or their components within an industrial facility.

Its significance lies in its ability to reduce noise levels in the immediate vicinity of the noise source. This is crucial for safeguarding workplaces situated in proximity of inhabited centers, especially when dealing with noise emanating from within production halls.

Practical experience indicates that enclosures play a pivotal role among the array of anti-noise protection measures employed to mitigate excessive industrial noise impacting acoustically shielded areas. Scientific research into the application of sound-absorbing and insulating enclosures has been ongoing for many years within various highly industrialized ecosystems.


Types of enclosures

In practical implementation, four types of enclosures are commonly utilized: partial, partially closed, fully closed, and integrated enclosures. On the other hand, the constructional solution of the enclosure is influenced by various factors, including the type and operational principle of the noisy machine, its production or technological process, and the specific requirements for a given acoustic insulation standard.








Fig. 1, Source: Enclosure solution studies of acoustic effectiveness under real conditions (J. Sikora)

In addition to the classification outlined earlier, further categorizations can be established by considering more detailed criteria, including:

  • Thermal requirements related to the enclosed machine;
  • Accessibility to the machine for repairs and during the course of production or technological processes;
  • The nature of the technological or production process undertaken by the enclosed machine;
  • The necessary acoustic effectiveness of the enclosure;
  • The incorporation of automation elements in the constructional design of the enclosure;
  • The shape of the enclosure.

Factors influencing the acoustic effectiveness of Enclosures

A measure of the enclosure effectiveness is represented by its acoustic insulation Dobud, which indicated to what extent the enclosure protects against the penetration of the air vibration as well as the material vibration within the outside.

The acoustic insulation of an enclosure primarily relies on the specific acoustic properties of its walls. The effectiveness of the enclosure’s acoustic insulation is determined by the physical characteristics of the construction materials and the overall design. Moreover, the acoustic insulation of the enclosure walls is influenced by material factors such as the volume density of the wall material, the longitudinal modulus of elasticity, the internal loss coefficient within the wall thickness, the frequency of the incident sound wave, and the void ratio of the wall material.

Additionally, various constructional factors impact the acoustic insulation characteristics of the enclosure wall, including:

  • The acoustic homogeneity or heterogeneity of the wall surface;
  • The types of joints and the method of fastening the wall to the structure;
  • The overall tightness of the wall across its entire surface, and so on.

Application of Acoustic Enclosures by Stopson Italiana: a few case studies

Stopson Italiana has been a player in the global soundproofing market for decades, serving as a leading manufacturer of soundproofing enclosures and control cabins. The equipment offered by Stopson Italiana is designed to meet high-level technical specifications and cater to custom-made requirements, effectively providing solutions for acoustically isolating noisy machinery or establishing quiet rooms.

Key offerings include:

  • Machinery Soundproofing: This involves enclosing machinery within specialized enclosures, ensuring comprehensive protection against noise by effectively isolating the noise source.
  • Soundproofed Control Cabins: Stopson Italiana provides soundproof control cabins to shield operators from external noise. These cabins are applicable in various settings such as in-plant offices, control booths, test cabins, control rooms, and electro-acoustic laboratories.

This range of solutions reflects Stopson Italiana’s commitment to addressing diverse soundproofing needs across different industries and environments. Stopson Italiana has successfully implemented its Acoustic Enclosures through successful projects around Italy and not only, helping different types of industrial setting overcome their noise-insulation challenges.

Some of our success cases:

  • 4 Acoustic Enclosures had been installed and allocated to the gas turbines, generators and auxiliaries within the 800 MW gas-fired power plant, located in the municipality of Turbigo, Italy. Read in detail HERE.
  • The supply of 3 Acoustic Enclosures had been brough to completion in the Trigeneration Power Plant – a combined electricity and thermal power plant – of Rovera, Italy. Read in detail HERE.
  • Acoustic Enclosures have been chosen as the most effective soundproofing intervention for the Enel Green Power plant (hydroelectric power plant) in Bordogna, Italy. Read in detail HERE.

Noise control. An historical excursus

Exposure to high noise levels poses significant risks of permanent hearing loss. Many industries are thus highly motivated to discover cost-effective solutions to address this issue.

The absence of suitable acoustic treatment in industrial setting can, in the best-case scenarios, disrupt the productivity of individuals within these spaces. Even if the noise is not harmful or particularly bothersome, it becomes undesirable when it hinders effective communication among coworkers.

As we have already discussed, much can be done to reduce the seriousness of noise problems. Effective equipment and methods are available for eradicating the noise generated by several engineering systems.

Have you ever considered the origins of these developments? This article offers a comprehensive examination of the historical evolution of industrial soundproofing.


Industrial noise control: historical background

Acoustics, owing to its connection with music, has been a subject of interest for many centuries.

It can be traced back to the Greek philosopher Pythagoras, who conducted early investigations into the physical origins of musical sounds around 550 BC. He observed that when two strings on a musical instrument are plucked, the shorter string produces a higher-pitched sound than the longer one. Notably, if the shorter string’s length is halved compared to the longer one, it emits a note that is one octave higher, signifying a twofold difference in frequency or pitch.

This foundational understanding led to the practice of measuring sound across standard octave bands or frequency ranges encompassing one octave. As a matter of fact, determining the frequency distribution of machinery-generated noise is critical for choosing effective noise control methods.

Credit is generally attributed to the Franciscan friar Marin Mersenne (1588–1648) for the earliest published analysis of string vibration, which he presented in 1636. Mersenne measured the vibrational frequency of an audible tone (84 Hz) produced by a long string. He also noted that the frequency ratio for two musical notes separated by an octave was 2:1.

A well-known scientist has made significant contributions to the field of sound control: in 1638, Galileo Galilei published a treatise on the vibration of strings, in which he established quantitative relationships between the frequency of string vibration, its length, tension, and density. Galileo observed that when different pendulums with varying lengths were set in motion, the resulting oscillations created pleasing patterns if the frequencies of these pendulums had specific ratios, such as 2:1, 3:2, and 5:4, corresponding to the octave, perfect fifth, and major third intervals in music.

In 1713, the English mathematician Brook Taylor, who is also known for developing the Taylor series, mathematically solved the shape of a vibrating string. His equation allowed for the derivation of a formula for the string’s vibration frequency that perfectly matched the experimental findings of Galileo and Mersenne.

In the early stages of acoustics, a precursor to the stethoscope was developed by French physician Rene Laennec in 1819. This device was employed for clinical purposes. In 1827, Sir Charles Wheatstone, a British physicist known for inventing the Wheatstone bridge, created an instrument similar to the stethoscope, which he named a “microphone.”

Following the invention of the triode vacuum tube in 1907 and the initial development of radio broadcasting in the 1920s, electric microphones and loudspeakers became available. These innovations paved the way to produce precise instruments designed to measure sound pressure levels and other acoustic parameters with greater accuracy than the human ear could provide.

Between the 1930s and 1940s, noise control principles started being applied to various areas, including buildings, automobiles, aircraft, and ships. During this time, researchers also began exploring the physical processes involved in sound absorption by porous acoustic materials.

With the outbreak of World War II, there was a renewed focus on addressing speech communication issues in noisy environments, such as tanks and aircraft. In the US, the National Defense Research Committee established two laboratories at Harvard University to tackle these concerns: the Psycho-Acoustic Laboratory studied sound control techniques in combat vehicles, while the Electro-Acoustic Laboratory researched communication equipment for noisy environments and acoustic materials for noise control. After the war, noise control research continued at various universities.

Post-war, noise problems in architecture and industry were finally addressed. Research was directed at solving residential, workplace, and transportation noise issues predominantly. An important development for industrial soundproofing was the 1969 US amendment to the Walsh–Healy Act, which imposed strict limits (e.g., 90 dBA for an 8-hour period) on noise exposure for industrial workers. This law also mandated the provision and training in the use of personal hearing protection devices if the noise exposure couldn’t be prevented.


Contemporary industrial noise control

The 1969 US amendment escalated a series of environmental regulations that were aimed at tackling noise pollution at a global level. Starting from 1970s, industrial facilities around the world were finally required to meet specific noise level standards, driving the need for effective soundproofing solutions.

During this period, industrial soundproofing primarily relied on traditional methods like installing acoustic panels, enclosures, and barriers. These methods were effective but often bulky and expensive. Nevertheless, these are still largely employed nowadays.

The 1980s and 1990s brought advancements in acoustic materials. On the one hand, these decades saw the development of innovative materials that offered better sound absorption and noise isolation properties. Fiberglass, mineral wool, and other materials became popular choices. On the other hand, advancements in manufacturing and construction technologies allowed for more efficient installation of soundproofing solutions. This period also witnessed the introduction of computer simulations for noise control design.

During the 2000s, the focus had been shifted on growing environmental awareness to make soundproofing measures more eco-friendly. Recycled and sustainable materials at this point gained more and more popularity. At the same time, manufactures began offering customized designs to address specific industrial noise challenges effectively.

Stopson Italiana has been an integral part of the industry’s evolutionary journey. With over 56 years of operational history, Stopson Italiana asserts its position as a leading company in the global noise control sector.

Our distinguishing factors include:

  1. Decades of experience, driving ongoing product enhancement;
  2. Tireless dedication to advancing technology and competitiveness;
  3. Profound expertise in soundproofing techniques;
  4. A track record of overseeing thousands of successful installations in various case studies.

Particularly, Stopson Italiana have become a company of choice when it comes to customizing service and product according to specific customer needs.

Learn more in detail about our soundproofing solutions HERE.

Different types of noise sources in industrial plants

Within industrial plants, while designing solutions for noise control, it is crucial to estimate how loud a specific noise source might be, especially in absence of actual measurements for any specific source.

But first, it is imperative to identify which are main noise sources and their characteristics. The goal of this article is to examine the main noise sources from several mechanical systems in industrial plants.


Main noise sources


1. Fan noise

Industrial fans come in different types with distinct noise features:

  1. Centrifugal fan with airfoil blades: used in large heating, ventilation, and air conditioning systems for clean air.
  2. Centrifugal fan with backward curved blades: used for general ventilation and air conditioning, with higher efficiency.
  3. Centrifugal fan with radial blades: commonly used in material handling systems.
  4. Centrifugal fan with forward curved blades: used for low-pressure and low-speed applications like home air conditioning.
  5. Tubular centrifugal fan: used in heating and ventilation for low-pressure return-air systems.
  6. Vaneaxial fan: suitable for medium to high-pressure applications but tends to be noisier.
  7. Tubeaxial fan: used in low to medium-pressure applications.
  8. Propeller fan: suitable for handling large volumes of air, used in roof exhaust systems and cooling towers.


2. Electric motor noise

While individual electric motors are not usually very excessive, the noise can add up when managing different machines together. Various factors contribute to motor noise, including windage noise from cooling fans, rotor-slot noise, rotor-stator noise, magnetic flux changes, dynamic unbalance, and bearing noise.


3. Pump noise

Pump noise comes from hydraulic and mechanical sources. Key noise sources include cavitation, fluid pressure fluctuations, impact on solid surfaces, and rotor imbalance. Proper vibration isolation can reduce structure-borne noise from pumps.


4. Gas compressor noise

Gas compressors belong to the category of machinery where it is crucial to prioritize efficiency and durability over noise reduction. Many gas compressors are not designed with low noise emission as the primary design criterion. Therefore, typically, noise control measures are implemented post-construction. The variables influencing noise levels encompass the compressor’s power input, the turbulence of the fluid, and the nature of the gas being compressed.


5. Noise from gas vents

One of the more serious noise problems in industrial plants is the noise produced by the discharge of air, steam, or process gas into the atmosphere. Blow-off nozzles, steam vents, and pneumatic control discharge vents are some examples of noisy venting situations. Noise from these vents results from turbulent mixing, and the frequency of the noise depends on the size of the turbulent eddies.


6. Valve noise

Valves and regulators used with steam and gas lines can be a significant source of noise. There are two primary sources of noise generated by valves: (a) mechanical noise generation and (b) fluid noise generation, either hydraulic for liquids or aerodynamic for gases.

Mechanical noise comes from pressure fluctuations and fluid impingement, while fluid noise is either hydraulic or aerodynamic. Valve vibration noise can indicate potential issues with the valve.


7. Air distribution system noise

In heating, ventilation, and air conditioning (HVAC) systems, noise can be transmitted from the air-handling unit into the duct system. Additional noise may be generated as air flows through various components like elbows, fittings, grills, and diffusers.


Measures for noise control

Understanding and managing these different noise sources is crucial for maintaining a comfortable and safe working environment in industrial plants.

To effectively manage noise as it travels from its source to the receiver, typically a worker, a careful consideration of certain procedures is imperative in order to select the most suitable infrastructure within the industrial plant. Among the most proficient soundproofing procedures are:

  • Employing Vent Silencers (for valves and tanks) designed to lower the noise levels produced by exhaust piping for pressurized gaseous fluids when vented to the atmosphere.
  • Utilizing Acoustic Barriers, whether in the form of single walls, partial enclosures, or full enclosures for entire pieces of equipment.
  • Installing Enclosures around noisy components within machinery.
  • Implementing either Reactive or Dissipative Mufflers: the former for addressing low-frequency noise or smaller exhausts, and the latter for dealing with high-frequency noise or larger diameter exhaust outlets.
  • Incorporating In-line Plenum Chambers or lined ducts into air handling systems.
  • Managing reverberation by adding sound-absorbing materials to spaces with excessive reflected noise. It is important to note that this approach may not significantly affect the direct sound reaching the receiver.
  • Exploring active noise control techniques, which involve manipulating the reflection, suppression, or absorption of noise emitted by an existing sound source through the use of one or more secondary or control sources.

Discover Stopson Italiana’s offering and find the solution that best fit your requirements HERE.

Acoustic measurements in industrial soundproofing. An introduction to the main instruments and parameters

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.

Acoustic criteria: how to protect your workforce from permanent hearing damages

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.

Types of industrial silencers and how to choose the right one

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.


Anechoic and Hemi-Anechoic Chambers: application context, design, and main benefits

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.