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Asia Noise News Environment

10 km of new MRT noise barriers in Ang Mo Kio, Buona Vista completed

SINGAPORE – Residents in Ang Mo Kio, Bukit Batok and Buona Vista are now enjoying slightly quieter neighbourhoods, with MRT tracks near their homes equipped with noise barriers that dampen the clunking of passing trains.

As of June, the second phase of the Land Transport Authority’s (LTA) project to build 27km of noise barriers along Singapore’s elevated tracks of the North-South and East-West MRT lines has been completed, spanning 10km and covering twenty locations.

Together with the first phase that was finished in 2018, 21.5km of MRT tracks are now covered by a semi-enclosure or flanked by vertical boards up to 4.5m high that can reflect or absorb sound waves.

The third phase, comprising another 5.5km in places like Joo Koon, Bishan and Paya Lebar, is set to be finished in 2024.

“You might not think that it is important – but it is,” said Mr Jen Ang, 56, a marketing director in Ang Mo Kio, who compared the dull thud of passing MRT trains to having a constant, although barely noticeable, headache.

“It happens every few minutes, sometimes it’s louder when two trains are close. At the end of the day, you are left exhausted and feel less energetic.”

He said the situation has improved now with the noise barriers up. “At least I’m no longer woken up by the sound of trains in the morning. And I get to enjoy my morning coffee.”

 

The locations of noise barriers are chosen based on various factors, including how close the tracks are to nearby homes. It is not clear what the total distance of MRT tracks above ground is.

Research has shown that a passing MRT train can produce noise of up to 80 to 85 decibels – the equivalent of the sound of a loud alarm clock or hairdryer. This is similar to noise levels of trains elsewhere and studies have shown that long-term exposure to this noise level can harm people’s hearing.

LTA’s barriers reduce the noise level by five to 10 decibels, as measured from the nearest residential block. The authority said previously that the resulting 75 to 80 decibel noise would be like listening to someone practising on the piano.

The project began in 2013 after residents complained about the noise from the tracks. The second phase of the project was initially due to be completed in 2019, but the Government decided to push back the date to this year as it needed to review the effectiveness of phase one of the project.

Some residents, like Ms Kong Si Min, 37, who lives near the train tracks in Ang Mo Kio, said she was counting down the days to the erection of the barriers.

Ms Kong, a business consultant, said the noise was particularly hard to bear during the period of pandemic restrictions, when she had to stay home more.

“It was then that I realised how debilitating (the noise) can be. I hope the Government continues to look into reducing noise from the trains, which definitely can still be heard.”

Today, the LTA is also exploring other ways to reduce the noise of transport infrastructure, such as with noise-dampening wheels and using ballast and concrete sleepers so tracks can more effectively absorb noise.

In 2019, then transport minister Khaw Boon Wan said developers of nearby buildings must chip in to design features that will reduce the noise from MRT tracks, as MRT noise can never be completely eradicated.

“Developers know about our rail and rail projects years in advance of their construction,” he said.

Transport Minister S. Iswaran said on Facebook last week that the installation of the barriers has not been easy. Time and effort were required to set up the barriers safely along a live MRT line without damaging existing infrastructure, he said.

Noise barrier installation takes place only after passenger service hours and is coordinated with other rail maintenance and improvement works.

During the construction of the barriers, mobile noise shields were used to reduce the impact on residents. Noise levels were also closely monitored in real time.

“I seek residents’ continued understanding on this,” Mr Iswaran said. “When the project is done, residents can look forward to a quieter neighbourhood.”

The National Environment Agency recommends that people should be exposed to no more than 67 decibels of noise level.

However, a National University of Singapore study in 2017 found that Singapore’s average outdoor sound level throughout the day was 69.4 decibels, exceeding the recommended level.

 

Source

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Asia Noise News Environment

Shah Alam, Residents affected by noise want highway sound barrier restored

The former sound barrier that was later removed for the highway expansion works

Residents of Pinggiran Golf Saujana Resort in Shah Alam, Selangor, have been living with noise pollution since the sound barrier at the nearby highway was removed in 2013.

They want it restored but claim their pleas to relevant authorities have fallen on deaf ears.

The residents said the sound barrier along the New Klang Valley Expressway (NKVE) from KM13 to KM13.5 was removed for the fourth lane widening works.

The residents’ representative, who didn’t want to be identified, complained that the noise had doubled over the years.

“Some residents even had to vacate their bedrooms facing the highway because they could no longer sleep peacefully.

“We have been patiently waiting for the authorities’ help for nine years now,” said the resident.

The affected residents hired a specialist consultant to conduct a noise survey in 2015. The study revealed that the noise level was over the limit allowed in the Environment Department’s guidelines.

“The authorities are welcomed to conduct their own survey so that they can understand our dilemma,” added the residents’ representative.

Shah Alam’s area councillor Kumareval Subrayan said he had visited the site and was aware of the issue.

“I will raise this matter at Shah Alam City Council’s upcoming full board meeting,” he said.

Source The Star

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Asia Noise News Environment

Korea: Residents of Pyeongtaek to Receive Compensation for Military Noise Pollution

compensation for aircraft noise korea
compensation for aircraft noise korea

PYEONGTAEK, Jan. 3 (Korea Bizwire)

About 63,000 residents of Pyeongtaek will receive monthly compensation for noise pollution coming from a military airport in the city, officials said Monday.

According to the government of Pyeongtaek, a city about 70 kilometers south of Seoul, the residents of 10 administrative units, including Sinjang and Paengseong districts, will receive monthly compensation from August under the military noise pollution compensation act which took effect last year.

compensation for aircraft noise korea
compensation for aircraft noise korea

South Koreans and foreigners who have been registered as residents of the districts between Nov. 27, 2020, and Dec. 31, 2021, are eligible for compensation application.

A monthly settlement of 60,000 won (US$50.30) will be provided per resident living in an area suffering noise pollution of 95 wecpnl or higher, 45,000 won for pollution of between 90 wecpnl and 95 wecpnl and 30,000 won for pollution of between 80 wecpnl and 90 wecpnl.

Wecpnl is a comprehensive unit measuring aircraft noise levels.

The city’s deliberation committee will review the applications and deliver the results by May, officials said.

source

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Environment

George Town Malaysia: Factory buses causing noise, complain residents

factory buses cause noise nuisance george town malaysia
factory buses cause noise nuisance george town malaysia

Factory buses causing noise, complain residents

GEORGE TOWN: Residents in the Relau neighbourhood in Paya Terubong, Penang, are upset over the noise pollution caused by factory buses.

They said this problem had been going on for more than 10 years with the authorities not taking any remedial measures.

Relau is a mixed neighbourhood, where low-cost flats exist together with expensive properties.

The problem began when some of these low-cost flats were turned into hostels for foreigners working in factories in the Bayan Lepas Free Industrial Zone.

Factory buses often enter the neighbourhood to pick and drop these workers.

At a press conference today at the Sierra East condominium, the Penang Relau Residents Association said the driving habits of these bus drivers also endangered the lives of residents.

“The roads in the neighbourhood are narrow and these buses are too big.

“Some of our residents have experienced close calls with these buses almost hitting their cars at T- junctions,” said Keane Ng, representative of the Penang Relau Residents Association who chaired the session.

He said there was noise pollution when the bus drivers started to park their buses along the roads.

“They start their engines as early at 4am,” said Ng.

He said the parked buses caused traffic congestion.

Ng said the noise pollution and the hostels for foreign workers had led to a depreciation in the value of their properties.

Ng called on the Association of Companies in Penang Industrial Zone (Frepenca) to resolve the problem by designating special parking depots for the buses that are located far from their neighbourhood.

factory buses cause noise nuisance george town malaysia

He said Paya Terubong assemblyman Yeoh Soon Hin had promised to find a solution to their woes by introducing road bumps and height gantries.

“We have also raised this matter with chief minister Chow Kon Yeow.”

Back in 2018, The Star reported that the Penang state government had identified two sites in Bayan Lepas as factory bus depots.

Earlier in February, factory bus operators said the lack of such depots had forced them to park in residential areas.

Source

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Environment Uncategorized

Noise complaints lead to drug bust in Thailand

noise complaints lead to drug bust Thailand
noise complaints lead to drug bust Thailand

You can make some noise, or you can break some laws, but you should avoid doing both. After neighbours complained of a Pathum Thani condo in a luxury building making excessive noise, police checked it out and uncovered a drug-dealing operation. The investigation led to several arrests.

The Department Of Provincial Administration joined the district chief of Klong Luang in Pathum Thani to investigate the noise complaint and ended up setting up a sting operation that culminated in a drug bust instead of just a noise violation.

noise complaints lead to drug bust Thailand
noise complaints lead to drug bust Thailand

The sting offered a low-level drug deal of just 500 baht and ensnared a 26-year-old Thai man and a 24-year-old Thai man who was a fourth-year university student. The Pathum Thani bust recovered the 500 baht from the drug deal as well as 2 full marijuana plants and imported heads for growing, weighing just over 46 grams. Other paraphernalia and evidence was seized too.

The raid was a small one, but police leveraged the young dealers to try to climb up the supply chain for a more significant bust. The 2 small-time dealers rolled over on another location in Pathum Thani just a few kilometres where police encountered 4 people doing drugs.

Police found and seized 514 grams of compressed marijuana on the premise in the second bust. They also made 2 more arrests related to the case including following the trail from the busts to locate and arrest a drug runner who was stopped in the middle of a delivery. He had 182 grams of marijuana on him.

The man claimed that he had no idea that the parcels he was delivering contained illegal drugs, saying that a woman who looked like a normal vendor told him he was just delivering cakes, for which he was paid a mere 280 baht.

Source

 

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Regulations, guidelines, and standards regarding environmental noise in Indonesia

With all the development, industrial activities and community activities in Indonesia, noise has become one of the problems that arises in some places in Indonesia. Indonesia already has some regulations, guidelines, and standards to safeguard the noise levels. This is important mainly to support a healthy environment for the people, and also to improve budgeting certainty of projects that will produce noise during their operations.

The following are the regulations, standards and guidelines related with environmental noise in Indonesia.

Environmental Noise Regulations

Regulations regarding environmental noise generally can be categorized into two types which are emission regulation and immission regulation. Emission regulations regulate how much noise can a noise source produces noise, while immission regulation regulates how much noise can a receiver or area receives noise.

Examples of noise emission regulations in Indonesia are:

  • Decree of Minister of Environment and Forestry No. 56 year 2019 (P.56/MENLHK/SETJEN/KUM.1/10/2019) regarding noise limits of new types of motorized vehicles and in production M category, N category, and L category.
  • Decree of Minister of Transportation of Republic of Indonesia No. PM 62, year 2021 regarding civil aviation safety section 36 regarding noise standard dan type certification and aircraft airworthiness

The two ministerial decrees above regulate how much noise can be produced by vehicles that are used on road and aircraft that can operate within Indonesian territory.

The regulation that regulates environmental noise level at the receiver is:

  • Decree of Minister of Environment No. 48 year 1996 about noise level limits

 

The decree states the noise limits that are allowed for the receiver according to its function – for example for residential area, the noise limit is 55 dBA and for industrial area 70 dBA. More details on the following link: https://www.konsultasi-akustik.com/en/environmental-noise-measurement/

 

Beside the regulations above, there are other requirement such as one written on Government Regulation (PP) No. 36 year 2005 regarding implementation rules of the Law No. 28 year 2002 regarding buildings. One of the points require noise reduction means for toll roads in residential area or existing city centers.

 

Guidelines regarding Environmental Noise

 

Beside the regulation, there are some technical guidelines that are written by Ministry of Public Works as follows:

  • Technical guidelines Ditjen Bina Marga No. 36 year 1999: Noise barrier planning guidelines
    In these guidelines, criteria to categorize area as safe, moderate and high risk are given. Moreover, the guidelines also state measurement techniques for measurement beside road and common type, shape and material of noise barriers.
  • Construction and building guidelines Pd T-10-2004-B: Road traffic noise prediction.

These guidelines adopt calculations from Calculation of Road Traffic Noise (CoRTN, UK, 1998) which contain noise calculation method based on traffic volume and speed. There are also corrections for heavy vehicle percentage, speed, gradient and road surface. From this calculation, propagation to receiver can be calculated considering distance, screening, reflection and angle of view.

  • Construction and building guidelines Pd T-16-2005-B: Mitigation of road traffic noise

The guidelines lay out methods to mitigate noise from traffic which is based on measurement (which are written on Permen LH No. 48 year 1996 and guidelines No.36 year 1999 above) and can also be based on predictions (Following construction and building guidelines Pd T-10-2004-B)

 

Environmental Noise Standards

 

Beside the regulations and guidelines, there are Indonesian National Standard (SNI) document that are written by National Standardization Body (BSN) that are related to environmental noise:

  • SNI 19-6878-2002 – Road traffic noise test L10 and Leq
    This standard contains test method which state testing procedure and data processing steps to calculate LA to L10 and Leq
  • SNI 8427:2017 – Pengukuran tingkat kebisingan lingkungan
    This standard contains measurement method that is similar to Kepmen LH No.48 year 1996 which is to measure noise samples for 10 minutes across 24 hours period. Noise levels then can be calculated based on its time slice which are Ls (daytime noise), Lm (nighttime noise), and Lsm (day-night noise, with 5 dB penalty for nighttime).
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What you need to know about Room Acoustics

In the Southeast Asia region especially, acoustic properties of residential buildings are often neglected by designers, developers, contractors, and even home buyers. Noises from both internal and external environments affects occupants’ daily lives, causing nuisance which can strongly deteriorate one’s living quality as a long-term effect. In this article, we will investigate building/room acoustics, and the actions that can be undertaken to improve the acoustical environment inside a building.

Room acoustics

In general, the acoustics of rooms can be divided into two groups: low frequency and high frequency. Sound in rooms can be highly affected by the reflective properties of the surfaces in the room. This is because multiple reflections may occur if the room surfaces are highly reflective, which then leads to a reverberant field in addition to the direct field from the source especially at higher frequency range. Therefore, at any point in the room, the overall sound pressure level is influenced by the energy contained in both the direct and reverberant fields (Crocker, 2007).

Sound transmissions in buildings

Sound can be transmitted within a building by transmitting through air in the spaces bounded by walls or roofs/ceilings, known as airborne transmission. Another way would be through structural transmission through the structural assemblies of the building, or impacts.

Airborne sound originates from a source that radiates sound waves into the air, which would then impinge on the building surfaces. A good example of airborne sound will be speech, or music from a television or loudspeaker. On the other hand, impact sound is being generated when an object strikes the surface of a building. The commonly heard impact sounds that we can hear in buildings are footsteps, furniture-dragging sounds, cleaning, and other equipment that is used directly on the floor surfaces. To overcome these noises, good sound isolation should be considered for all the possible paths for sound and the junctions between walls and floors, not just at the direct path through common wall or floor.

Sound insulation – airborne and impact

It is imperative to consider the control of airborne and impact sound transmission through the building elements like walls, ceilings, or floors, as stated above. In this case, sound insulation methods will be crucial. Different methods can be implemented for airborne, impact and flanking sounds (Crocker, 2007).

For airborne sound, insulation can be applied at any building element. This is because when sound hits on a surface, a very small fraction of the incident energy will be radiated from the other side. The sound transmission loss (TL), which is the ratio of the incident sound energy relative to the transmitted sound energy is typically measured. TL can be expressed in decibels (dB), and it is sometimes known as sound reduction index (R) in European and ISO standards. The elements to be used in buildings for sound insulation are measured in accordance with standards, where the commonly seen method would be the two-room method. A test specimen would be mounted between a reverberant source room, and a receiver room such that the only significant path for sound to transmit through is the specimen, and other possible transmission paths would be suppressed. As such, it will be useful to determine the TL of the building elements/materials so that one can estimate the airborne sound insulation performance inside the building space.

As for impact sound which typically radiates from a floor into rooms below or horizontally, insulation can be done via floor coverings or floor slabs. This is because the applications of these items can reduce the impact sound pressure levels that travels into the receiver room. The typical methods of insulation are adding soft floor coverings on concrete slab, increasing the thickness of concrete floors, or implementing floating floors.

Single number ratings

To know the acoustic information of an insulation element, the standard method would be to refer to the single number ratings of that element. These ratings would be assigned to building materials based on their sound transmission spectra by the means of reference curves or weighted summation procedures.

The most used single-number rating for airborne sound insulation is the Sound Transmission Class (STC), which is in accordance with the American Society for Testing and Materials (ASTM) E413. There is another equivalent number called the Weighted Sound Reduction Index (Rw), which is based on the International Organization for Standardization (ISO) standard ISO 717.

The figure above shows an example of STC contour fitted to a concrete slab’s data. The differences between data points below the contour line and the value of contour are called the “deficiencies”. According to ASTM E413, the sum of deficiency should not be greater than 32 dB, and each individual deficiency should not exceed 8 dB (also known as the 8-dB rule). The reference contour for ASTM covers the frequency range from 125 Hz to 4000 Hz. The Rw contour from the ISO 717 has the same shape, except that it covers a broader frequency range of 100 Hz to 3150 Hz. Also, there is no 8-dB rule in ISO 717. Comparing both standards, the numbers from both ratings are usually close. However, the weighted summation method developed in ISO 717 accounts for the higher importance of low frequencies in traffic noise and modern music systems. As such, this method allows corrections/spectrum adaptation terms to be produced that can be used in conjunction with the Rw rating.

As for impact sound insulation, the sound pressure levels are often collected using a standard tapping machine and normalised, which will then be used with a reference curve to calculate its rating, typically the Impact Insulation Class (IIC), or the weighted index Ln,w. In fact, these ratings are commonly used in building codes. Again, the rating curves are identical in each standard, but there are some differences among them still. For instance, the ASTM IIC method does not allow any unfavourable deviation to exceed 8 dB. An increasing IIC rating would indicate that the impact sound insulation improves. Conversely, the Ln,w rating would decrease as the impact sound insulation gets better. We can take the relationship between both ratings as follow (assuming that the 8-dB rule is not invoked):

However, there is debate regarding the usefulness of ISO tapping machine data obtained on different types of floors. Therefore, the latest version of ISO 717-2 proposed the use of C1, a spectrum adaptation term to consider low-frequency noise that is normally generated below a lightweight joist floor.  is the unweighted sum of energy in the one-third octave bands (50 or 100 Hz – 2500 Hz) minus 15 dB. According to the standard, this rating is expected to have a better correlation with the subjective evaluation of noise coming below floors, especially for low frequency ones.

The single rating numbers mentioned above are all useful when it comes to determining the level of acoustic insulation a material can provide. With the explanation above about room acoustics and the insulation measures that can be implemented, it will give a better idea on how one should tackle and handle the room acoustics in a building.

References

Crocker, M. J. (2007). Chapter 103: Room Acoustics. In C. H. Hansen, & M. J. Crocker (Ed.), Handbook of Noise and Vibration Control (pp. 1240-1246). Adelaide, South Australia, Australia: John Wiley & Sons, Inc. doi:ISBN 978-0-471-39599-7

Crocker, M. J. (2007). Chapter 105: Sound Insulation—Airborne and Impact. In A. C. Warnock, & M. J. Crocker (Ed.), Handbook of Noise and Vibration Control (pp. 1257-1266). Ottawa, Ontario, Canada: John Wiley & Sons, Inc. doi:ISBN 978-0-471-39599-7

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Acoustic of Small Studio

Studio Acoustic

Small studios are now widely used in the recording industry due to their high feasibility and them being economically friendly, which allows those working in the recording/music industry to be able to work remotely without needing to travel to big studios that much. With a good implementation of acoustic treatments, music recorded in small studios can still be high in sound quality, sometimes even suitable for commercial release.

So, what makes a recording studio good?

In today’s article, we will look into the acoustics of small recording studios, where music is performed as recorded (Everest & Pohlmann, 2015).

Ambient conditions

A quiet environment is a must for a studio to be useful, which is sometimes quite hard to achieve. First, noisy sites should definitely be avoided as many noise and vibration problems will not arise by just choosing a site in a quiet location for your studio. Avoid places near loud areas like train tracks, busy road intersections, or even an airport. The ultimate idea is to reduce the external noise spectrum, then keep the background noise within the criteria goal by implementing sound insulations in the building. However, the construction costs of effective insulation elements like floating floors or special acoustically treated walls/windows/doors may cost greatly. Hence, the best way, that is more cost-effective, will be to choose a quiet site in the first place, rather than isolating a studio located at a noisy place.

The HVAC system, which includes heating, ventilating and air-conditioning systems should be designed such that the acoustics meet the required noise criteria goals. The noise and vibration coming from motors, fans ducts diffusers etc. should be brought to the minimum so that low ambient noise levels can be achieved.

Noise

Similar to any other quiet rooms, a small studio needs to comply with the acoustical isolation rules and standards. It is important to construct the building elements with high transmission loss and decoupled from external noise and vibration sources to ensure that the ambient noise levels are low enough for good recording quality. Not only that, but these constructions will also act as an isolation that prevents loud noise (music) levels in the studio from affecting the neighbouring spaces.

Studio acoustical characteristics

Inside a studio, the types of sound present, and may be picked up by microphones, are the direct and indirect sounds. Direct sound is basically the sound coming from the source (before it hits a surface). Indirect sound follows right after the direct, caused by various non-free field effects characteristic of an enclosed area. In short, everything that is not direct sound is considered as indirect or reflected sound.

It is known that the sound pressure level in an enclosed space will vary according to the distance from a source, while also being affected by the absorbency of the room or space. If all the surfaces in a room are fully reflective, it means that the room is fully reverberant (like a reverberation chamber), therefore the sound pressure level would be the same (as of the sound from the source) everywhere in the room as no sound energy is absorbed. It can also be assumed that there is relatively no direct sound since most of the sounds are reflected, hence indirect. Another component that causes indirect sound comes from the resonances in a room, which is also the result of reflected sound.

Indirect sound also depends on the materials used for room construction (e.g., doors, walls, windows, floors, ceiling etc). These elements can also experience the excitation by the vibration of sound from the source, hence able to decay at their own rate when the excitation is removed.

Reverberation Time

The composite effect of all the indirect sound types is reverberation. Many would say that reverberation time is an indicator of a room’s acoustical quality, but in reality, measuring reverberation time does not directly reveal the nature of the reverberation individual components, giving a small weakness of reverberation time being the indicator. Therefore, reverberation time is often not the only indicator of acoustical conditions.

Reverberation time is, by definition, the measure of decay rate, and is usually known as T60. For example, a T60 of 1 second represents that a decay of 60 dB takes 1 second to finish. Some may say that it is inaccurate to apply the reverberation time concept to small rooms, as a genuine reverberant field may not exist in small spaces. However, it is still practical to utilize the Sabine equation (for reverberation) in small-room design to make estimations on the absorption requirements at different frequencies, provided that limitations of the process are taken into account during the estimation.

It is not good to have it being too long or too short. This is because for a room with reverberation time that is too long, speech syllables and music phrases will be masked hence causing a worsening speech intelligibility and music quality. Conversely, if the reverberation time is too short, speech and music will lose character therefore suffer in quality, whereby music will typically suffer even more. Despite that, there is no specific optimal value for reverberation time that can be applied for any rooms, because too many factors are also involved besides reverberation. Things like the types of sound sources (female/male voice, speed of speech, types of language etc) will all affect the room’s acoustic outcome. However, for practical reasons, there are approximations available for acousticians to refer to, where certain amount of compromise has been implemented to make it usable in many types of recording applications.

Diffusion
A high diffusion room give a feeling of spaciousness due to the spatial multiplicity of room reflections, and it is also a good solution to control resonances effects. To create a significant diffusing effect, the implementation of splaying walls and geometrical protuberances works well. Another way will be to distribute absorbing materials in the room, which also increases the absorbing efficiency of the room apart from diffusion. Typically, modular diffraction grating diffusing elements (e.g. 2- x 4-ft units) can provide diffusion and broadband absorption, and can be easily installed in small studios. Still, there will not be much diffusion in a studio room, in practice.


Examples of acoustic treatment
So, what are the acoustic treatment elements that you can use to improve your studio? These items below can be considered (Studio, 2021):
1. Bass Traps
This is one of the most important tools to have in a studio. Bass traps are normally used to absorb low frequencies, also known as bass frequencies, but in fact they are actually broadband absorbers. This means that they are also good at absorbing mid to high frequencies too.

2. Acoustic Panels
Acoustic panels work similarly like bass traps, but rather ineffective at absorbing the bass frequencies. One thing good about acoustic panels as compared to bass traps is that since they are much thinner, they offer more surface area with less material. Therefore, acoustic panels are capable of providing larger wall coverage with less cost as compared to bass traps.

3. Diffusers
Diffusers may not be as effective as compared to bass traps and acoustic panels if used in small studios. So, this really depends on users, whether they find diffusers useful for their application.
Now, where should the acoustic treatment products be placed at?
There are three key areas of the room to be defined in this case:
– Trihedral corners
– Dihedral corners
– Walls
The priority for coverage goes from trihedral corners, dihedral corners to the walls. This is because acoustic treatments should ideally be placed at areas which have the greatest impact. At trihedral corners, for example, three sets of parallel walls converge, hence if there is absorption material located here, it catches the room modes from all three dimensions, giving three times the initial effectiveness. Same concept goes for dihedral corners and walls, but with two dimensions and one dimension respectively.

 

References
Everest, F. A., & Pohlmann, K. C. (2015). Acoustics of Small Recording Studios. In F. A. Everest, & K. C. Pohlmann, Master Handbook of Acoustics (6th Edition ed.). McGraw-Hill Education – Access Engineering. doi:ISBN: 9780071841047
Studio, E.-H. R. (2021). CHAPTER 3: The Ultimate Guide to Acoustic Treatment for Home Studios. Retrieved from E-Home Recording Studio: https://ehomerecordingstudio.com/acoustic-treatment-101/

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Noise Barriers

Noise barriers are designed to resist the sound waves in the propagation path from source to receiver. In general, the closer the barrier is to the source the more effective it becomes. For simple plane barriers the height and length are the most important factors determining the degree of screening achieved and simple design rules have been developed to determine the reduction in overall noise levels.  These are based on the path difference between the direct path from source to receiver through the barrier and the shortest path passing over the top of the barrier. The greater this path difference the greater the screening. The shadow zone of the barrier is the region where the receiver cannot see the source and here the greatest reductions in noise levels are recorded. Some sound will always be diffracted over the top and around the edges of the barrier into the shadow zone so it is not possible to eliminate all noise from the source. However, typical barriers of a few metres high can achieve a worthwhile noise reduction of the order of 10 dB(A). This corresponds to halving the subjective loudness of the sound.

 

Figure (a)

Figure (b)

For more complex barriers simple methods are not appropriate and numerical methods such as the Boundary Element Method (BEM) have been used to produce accurate solutions.

Many different types of barrier have been installed using a wide variety of materials including wood, steel, aluminium, concrete and acrylic sheeting. Some of these designs have absorptive facings on the traffic side which reduce reflected sound. Barriers over 8 m in height have been used for some applications and novel capped barriers and angled barriers have been tested.

Barriers that may offer improved performance over simple plane barriers can be grouped under the following broad headings.

The above fig (a) shows the Main pathway of the sound propagation from the source to the barrier’s edge for sound walls with or without source-side absorption. Fig (b) shows Absorption material construction.

If smaller vehicles passing by the barrier, the reflection off the vehicle it does not play much of a role. Multiple reflections can only occur if noise barriers are built along both sides of the highway or train tracks.

In the case of large noise emitters, the implementation of source-side absorbent noise barriers can prevent the so-called zigzag effect

  1. Absorptive barriers—that is, barriers incorporating elements on the traffic face that absorb a significant proportion of incident sound and hence reduce reflected sound which could contribute to overall noise levels in the vicinity.
  2. Angled barriers—that is, barriers that are tilted away or have contoured surfaces angled to disperse the noise, the aim being to prevent significant sound reflections into the area where screening is required.

 

ABSORPTIVE BARRIERS

Where a plane vertical barrier is erected on one side of the road then sound reflections to the opposite side take place as illustrated in fig 1(a). In addition, reflections between vehicles and the barrier may lead to loss of screening performance as shown in fig (b). Where plane vertical barriers exist on both sides of the road, as shown in fig(c), they are normally parallel to each other and, in this situation, sound is reflected back and forth between the barriers again leading to a loss in performance. Absorbing panels located on the sides of the barriers facing the traffic can reduce this reflected contribution by absorbing the sound energy from the incident wave.

ANGLED BARRIERS

An alternative to using sound absorptive barriers is to angle the barrier or parts of the barrier away from the road such that the reflected wave from the traffic face of the barrier is deflected upwards, so reducing the contribution to noise at receptor positions relatively close to the ground. The performance of such barriers has been measured at full scale at TRL’s unique Noise Barrier Test Facility (NBTF).  The noise source used consisted of an 800 W speaker that can be positioned in front of the test barrier on a specially laid strip of hot rolled asphalt, thereby representing the traffic source on motorways and all-purpose dual carriageway roads. Microphones can be positioned to measure the noise level in the shadow zone of the test barrier at any point on a wide flat grassland area free of reflecting objects. To measure the acoustic performance of the barrier, recorded noise in a broad frequency range is broadcast and noise levels are measured at standard locations behind the barrier. Corrections can be made for variations in speaker output and wind speed and direction. In this way the screening performance of the barriers for a typical traffic noise source can be evaluated.

The above fig shows angled noise barrier.

Source : Various books and research journal

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Noise caused by construction works at night in Netizen

A video she had filmed of the construction site shows the drone of the machinery could be heard reverberating along with the backup beeper of a truck at the site. This can go on up to 3 am as reported by the netizen.

Singapore — A member of the public has taken to Facebook after she realized that construction works were being carried out near her apartment even at night, causing a lot of noise in the area. 

She put up a post on the Facebook group “Complaint Singapore” to seek advice from other netizens who might have encountered a similar situation before.

In her post, a member of the public also included a video she had filmed of the construction site. In the video, the drone of the machinery could be heard reverberating along with the backup beeper of a truck at the site.

According to the caption of the post, this was not the first time that such an incident had occurred. The member of the public also mentions that the construction works had gone on until 3 AM on a previous occasion. As such, she asked other netizens for help on who to contact on the issue, since the sounds generated by the construction works can be quite loud and disruptive.

Other netizens shared their views on the matter and offered suggestions in the comments section. 

A few netizens chalked the nighttime construction down to urgency, saying that there might be an emergency that needs fixing quickly and promptly.

Some other netizens thought that carrying out construction work at night, would impede the flow of traffic less since there are fewer commuters during the night.

A few other netizens suggested that the poster bring the issue up to the relevant authorities such as the National Environment Agency (NEA), the Land Transport Authority (LTA), or the Singapore Police Force (SPF).

After contacting NEA, the poster replied that they were helpful in stopping the works at an earlier hour.

According to NEA, construction sites need to observe the noise level and exercise construction noise control with effect from 1 Oct 2007. 

Credits: www.theindependent.sg

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