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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. 

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The power of trees can reduce noise.

The way most workers need to complete tasks have significantly changed the way companies use their spaces. Quiet spaces are needed for deep, focused work. Technology enabled meeting rooms and collaboration spaces are used for productive meetings. Ideally, an office is designed in such a way that it enables team members to do their best work.

Unfortunately, it can be difficult to make sure a design includes all these aspects. As a result, designers and architects still often have to leave space for cubicles and open office spaces, a big contributing factor to general noise levels.

Did you know? Planting trees in your home or office not only helps to cool the internal temperature, increase the oxygen in the air give a feeling of freshness, and help relax only. But plants can also HELP ABSORB NOISE!

One creative way to both combat office noise and bring biophilic elements to a design is to incorporate plants and greenery into a space. Studies have shown that both plants and living green walls are an effective way to absorb sound and noise pollution.

Beyond their sound absorbing qualities, plants and biophilic elements can help to improve a worker’s overall well-being. Access to natural elements like greenery, natural light, and organic textures have been found to both improve employee productivity and reduce absenteeism. Plants have been found to be a mood booster and a stress reliever for team members, which can in turn, help to improve an employer’s bottom line.

Do Plants Help to Absorb Sound?

There is quite a bit of research on the subject, but the short answer is yes. The flexible and porous nature of indoor house plants acts as natural sound reducers. There are three ways that house plants can reduce the sound in your home or office: deflection, absorption, and refraction.

Most people do not understand the sound absorption benefits of houseplants. However, they really do help with absorption sound.

How Plants Reduce Indoor Noise Levels?

As mentioned above, plants reduce noise levels through three different methods: deflection, absorption, and refraction.

  • Deflection – Sound waves tend to bounce around off hard surfaces. That is where all that added noise comes from. Walls are rigid and will amplify sound, while plants are flexible and help to deaden the sound by breaking up the sound waves into other forms of energy.
  • Absorption – Plants are great at absorbing sound because of the leaves, branches, and wood. Wood is a great sound absorber. Have you ever walked through a forest and been amazed at the silence? That is because the trees are absorption all the ambient noise.
  • Refraction – Refraction is taking away the echoes of the sound bouncing off the hard surfaces. Plants will help to refract this noise and eliminate the echoes which are responsible for much of the added noise in your home or office.

The indoor plants that work best at absorbing sound such as:

  • Ferns: have a lot of surface space to help reduce sound. Their wide leaves spread out and cover quite a bit of area.
  • Baby’s Tears: Baby’s Tears are a dense plant that looks almost like moss. The plant has a way of draping itself over the pot and makes a great sound reducer when elevated off the ground.
  • The Peace Lily: The Peace Lily can absorb some of the sounds with their leaves and do a great job of bouncing the sound to the other plants and is a great sound absorbing plant you can put in your home. Their true noise absorbing properties are in their thick, broad leaves.
  • The Rubber Plant: The beauty of this plant is just how big it can get. Rubber plants cover a large surface area which only serves to enhance their sound absorbing properties.
  • Fiddle Leaf Fig: The fiddle leaf fig is another plant with broad, thick leaves. They can grow tall, and the cupped shape to the leaves make for an effective sound absorber.

Reference :

พลังจากต้นไม้ ลดมลพิษทางเสียง

https://bettersoundproofing.com/best-sound-absorbing-indoor-plants/

The Top Sound Absorbing Plants For The Workplace

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SCOPE OF ARCHITECTURAL ACOUSTIC CONSULTANT’S WORK

What should an architectural acoustic consulting firm do? This question is very commonly asked when an acoustician is asked to submit a work proposal for a project. In this article, we will describe the scope of work of an acoustic consultant with reference to the type of mixed-use high-end building project. Because in this type of project an architectural acoustic consultant is required to be able to describe all the scope of work in one project with high complexity.

Details of the scope of work of acoustic consultants in mixed-use high-end building projects are as follows:

1. Criteria Formulation
At the beginning of the project, the acoustic consultant must recommend design criteria/targets for various rooms and areas within the building such as retail, apartment units both for bedrooms and living rooms, and commercial areas such as meeting rooms, multifunction rooms, spas, fitness, restaurants. , club lounges, etc. These criteria are determined based on studies and summaries of the applicable standards in the country, international standards, client recommendations, and the building operator concerned.

2. Schematic
With so many rooms that fall into the scope of work of an acoustic consultant with this type of project, it is highly recommended that an acoustician provide schematic designs for several important rooms for the attention of other consultants in the early stages of the project. Examples are MEP rooms, building structure connections, placement of HVAC equipment above the ceiling, and draft wall partition configurations.

3. Noise Review from the Environment Around the Building
The acoustic consultant must review potential sources of noise from aircraft, train stations, transportation on highways, outdoor MEP equipment, and all things around the building that have the potential to interfere with audial comfort to the interior of the building to ensure the targeted acoustic criteria are achieved. At this stage the acoustician must be able to convey the results of modeling and simulations for several points around the building in the form of drawings that can be understood by clients and other consultants. At this stage, a building fa konfigurasiade configuration can be recommended that takes into account the noise from the area around the building.

4. Noise HVAC (duct-borne)
Discussion and review of noise from all HVAC be it from air handling unit (AHU), axial and centrifugal fans, fan coil unit (FCU), etc. The ducting system will be analyzed to determine the noise level in the critical room from the nearest diffuser ducting system outlet. From this analysis, the need for silencers, lagging or duct linings will be recommended in order to achieve the acoustic criteria that have been determined. The analysis will be carried out on all HVAC systems without exception, with the greatest attention being on residential areas, spas, hotels, etc.

5. Sound Propagation in Building Structures (Structure-Borne)
All matters relating to the propagation or vibration of sound via the building structure, whether it is due to human footsteps on the top floor or vibrations from the installation of MEP machines above the ceiling or floor. The acoustic consultant must be able to evaluate according to the natural frequency of the building structure and provide recommendations on floor slab elements to meet operator and client standards applied.

6. Machine Vibration Control
The acoustic consultant should conduct an in-depth discussion on the vibration isolator for the installed machines. This is done by taking into account the deflection of the floor slab and its relationship to the static and dynamic loads of the machine (eg chiller, pump, cooling tower, AHU, etc.). In addition, ensuring the insulator is efficient to withstand vibrations to the building structure.

7. Room Insulation
Discussion on the isolation of certain rooms by providing technical calculations both with the “indoor room” and “floating floor” methods so that sound and vibration do not propagate to all elements of the building, especially the room around the isolated area.

8. Acoustic Interior
Reviewing and calculating room acoustic parameters on interior design elements of commercial spaces such as ballrooms, meeting rooms, and other areas where the clarity of speech or music is crucial.

9. Detailed Drawing
The acoustic consultant must provide or recommend specifications for building skin elements such as faades, walls and floor slabs in CAD format on a cut or plan basis. This will make it easier for relevant consultants to apply these specifications in their construction drawings.

10. Noise Isolation Due to Impact
Collisions in the fitness area, whether it’s due to aerobic activity or lifting weights, are a special concern for acoustic consultants. In addition to different forms of acoustic treatment, the time span of these activities must also be included in detailed technical calculations, and of course measurable.

11. Review of Related Consultant Drawings
After all acoustic treatments have been adapted to construction drawings by the relevant consultant, the acoustician must review all these drawings to ensure that all treatments have been described correctly, before entering the tender phase.

12. Coordination with Selected Contractors
The acoustic consultant must allocate time to coordinate the design and answer questions from the selected contractor and sign all forms related to material approval if it is in accordance with the acoustic intentions.

13. Final assessment
Before handing over the project to the next party, the acoustic consultant must conduct a final assessment of the building elements designed by the consultant. Next, compare the measured value to the design target and pre-determined criteria.

by Ramadhan Akmal Putra 

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Accelerometer mounting

One of the challenges in measuring vibration using accelerometer is how to mount the accelerometer on the surface of the object that is being measured. Choosing the proper mounting can affect both to the measurement results and practicality when we are conducting the measurement.

 

Accelerometer mounting affects the measurement results because it can shift the resonance frequency of the accelerometer. Accelerometers have a significant amplification factor at its resonance frequency. This implies that in conducting measurements using accelerometer, it is important to choose mounting techniques that does not shift the resonance frequency into our frequency of interest.

 

Generally, there are four ways to mount accelerometer which are:

  1. Stud mounting: this technique is done by bolting the accelerometer into the object. This option is often considered as the mounting technique that produces the best measurement result compared to other options. Stud mounting has a high resonance frequency that in most cases a lot higher than our frequency of interest. To increase the performance of stud mounting, coupling fluid such as oil, petroleum jelly or beeswax can be used.

The downside of this technique is that not all object has a possible location to be bolted at the surface. If this is the case, then we will need to modify the surface and might leave a hole on the object.

  1. Adhesive: there are few adhesives that are commonly used to mount accelerometers such as epoxy (usually chosen for permanent mounting), wax, glue, and double-sided tape. Use of adhesive has lower resonance frequency compared to stud mounting, but in majority of cases still high enough that it does not affect the measurement at the frequency of interest. Of course, this depends on the type of adhesive that is being used as well.

Usage of adhesive however, especially for temporary mounting, has its own problem which is it can leave stain on the surface of the object that we are measuring, as well as on the accelerometer itself.

Another option of mounting related with adhesive is to use adhesive mounting pad, which is a pad that can be mounted on the surface that we want to measure using adhesive, and then we can mount the accelerometer on the pad. This will allow us to move one accelerometer to few locations more easily. From practicality perspective, adhesive mounting pad has an advantage if we want to repeat the measurement. Also, by using adhesive mounting pad, we avoid direct contact of adhesive to the accelerometer so that it will not need cleaning.

  1. Magnet: For metal surfaces, one of the options that is easy and does not leave stain is by using magnetic mounting base on the accelerometer so that we can attach the accelerometer to metal. This is the reason magnetic base is one of the best options especially for short-term and temporary measurement on metal.

However, this mounting technique produces lower resonant frequency compared to the other two options that we have discussed above. If the frequency that we want to measure is high enough, say above 1 kHz, this mounting technique might influence the measurement results.

  1. Handheld: In some of the cases, the three options above are not possible to be chosen, and it leaves us with the last option which is holding the accelerometer by hand. In this kind of cases, a probe tip can be used so that we can put pressure by hand on the surface that we are measuring easier.

We will have to pay more attention to the frequency range that we are measuring if this mounting technique is used. Because this option will reduce our frequency range significantly, generally only in the range of 10 – 100 Hz. 

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Industrial Noise Control Measure

In industrial places that are normally full of machineries or mechanical systems, noise is definitely inevitable, and in fact, very loud. This can sometimes be harmful to the workers hence causing occupational health and safety hazard. Therefore, in this article, we will look into noise control measures that can be used to overcome industrial noise in workplace.

Noise sources

Let’s begin with a recap on how noise is being produced:

Sound in general, is produced by vibration, or sometimes due to aerodynamic systems. Vibration-induced noises can be caused by multiple reasons, for example:

  • Mechanical shocks and friction between machinery parts like hammering, rotating gears, bearings, cutting tools etc.
  • Moving parts that are off-balanced
  • Vibration of large and heavy structures

As for aerodynamic noises, they are caused by air or fluid flows through pipes, fans, or pressure drops in air distribution systems as well. Typical examples of aerodynamic noise sources are:

  • Steam released through exhaust valves
  • Fans
  • Combustion motors
  • Aircraft jets
  • Turbulent fluid flow through pipes

Steps to control noise in workplace

To properly control the noise in the workplace, these steps should be carried out:

  1. Identify the sound sources (i.e., vibrating sources or aerodynamic flow)
  2. Identify the noise path from source to worker
  3. Determine the sound level of each source
  4. Determine the relative contribution to the excessive noise of each source and proceed to rank the sources accordingly. The dominant source should always be prioritised and controlled first in order to obtain significant noise attenuation.
  5. Understand the acceptable exposure limits as written in the health and safety legislation and find out the necessary sound reduction.
  6. Find out solutions while taking the degree of sound attenuation, operation, productivity restrains and cost into consideration.

To reduce exposure to noise

In general, noise exposure can be reduced by the elimination of noise source if possible, otherwise substitution of source with a quieter one or the application of engineering modifications works too.

The most effective way to minimise the exposure of noise is to engineer it out at the very beginning: the design stage. It is suggested to always choose equipment features that can reduce noise level to an acceptable level. For new installations, again select a quiet equipment, and make sure to have a procurement policy that opts for using quiet equipment, and finally eliminate any design flaws that may lead to noise amplification.

Engineering modifications refer to changes that can affect the source, or the sound path. This is usually the preferred solution for noise control in already-established workplaces (those without noise protection measures during design stage). This is because engineering modifications are known to be more cost effective, especially to control the noise at the source than along the path.

Administrative controls and the use of personal protective equipment (PPE) are also effective as measures of noise control applicable on workers themselves. A combination of both may be taken into consideration when the noise exposure would not justify the implementation of engineering solutions that are more expensive. However, it is important to always note that administrative control and PPE may not be as effective as implementing engineering noise control during the starting stage or modifications of sound path. Therefore, they should be categorised as the last resort.

Engineering solutions to reduce noise

Different solutions can be applied for vibration-induced noise and aerodynamic-noise.

For vibration-induced noise, the key point is to reduce the amount of vibration at the source. The typical solutions include modification of the energy source such as lowering the rotating speed of fans, or reducing the impact force of hitting tools etc. Adding damping materials onto vibrating surfaces due to mechanical forces can help to reduce vibrational effects too, especially for thin structures. To prevent unwanted damage due to friction or impact, the damping material may be sandwiched between the surface of equipment and another material that is resistant to abrasion. This treatment is called the constraint layer treatment.

Other methods to reduce vibration-induced noise include minimising gaps in machine guards and cover them with acoustic-absorbent material, replacing metal parts with plastic parts whenever possible, and replacing motors with quieter ones.

On the other hand, to treat aerodynamic-induced noise, specialists recommended to implement engineering practices that are capable of reducing noise associated with unstable fluid flow, for example minimising fluid velocity, increasing pipe diameter or minimising turbulence by utilising large and low speed fans with curved blades.

Besides those mentioned above, there are also passive noise control measures that can be used. These include using enclosures and isolations by storing noisy equipment in enclosed spaces/rooms that have special acoustic features like isolation, louvres or sealings. Installations of acoustic barriers (sound-absorbing panels) in workplaces, or silencers inside ducts and exhausts works well in attenuating unwanted noise too.

General measures to keep in mind

Finally, here are some general methods that one can take to ensure that workplace noise is under controlled.

Regular maintenance should always be performed, where the focus should be on identifying and replacing any worn-off or loose parts, lubricating any moving parts, and make sure that the rotating equipment does not get off balance to avoid vibration-induced noise.

Noisy processes should be taken note about and be substituted with quieter ones. Sound reverberation in the room should be reduced. Reverberation is when sound produced in an enclosure hits reflective surfaces and reflects back into the room in addition to the original noise paths. In some cases, reverberated sounds may dominate the original sound. A good method to help in such conditions will be to add padding onto the reflective surfaces with sound absorbing materials so that noise level can be reduced. Another way will be to arrange the equipment in the room so that they are not too close to too many reflective structures.

Conclusion

In conclusion, always take measures to identify the sound sources in the industrial workplace and find out suitable ways to solve the noise issues to achieve noise limits in accordance with exposure limits set in the health and safety legislation published by the local authorities. It is utmost important to obey the noise exposure limits to ensure the hearing health of workers in the workplace.

Reference

https://www.ccohs.ca/oshanswers/phys_agents/noise_control.html

https://www.who.int/occupational_health/publications/noise10.pdf

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Singapore to Ban Older Motorcycles

As motor vehicle emissions regulations tighten around the world, it should come as no surprise that Singapore is set to restrict motorcycles registered before July 1, 2003, and effectively ban them after June 30, 2028. The island city-state is under 800 km2 in area, yet is home to 5.7 million residents (denser than Hong Kong), and is known for its strict laws, cleanliness, and low crime rate.

The restrictions were introduced in 2018, and Singapore’s National Environment Agency (NEA) released new information and guidelines on the emissions regulations and standards in April of this year. The laws come into effect on April 26, 2023, after which time, qualifying motorcycles must meet tighter emissions standards of “4.5% Carbon Monoxide (CO) by Volume; and 7,800 ppm Hydrocarbons (HC) (for 2-stroke engine) or 2,000 ppm HC (for 4-stroke engine)”, as per the NEA documentation. After June 30, 2028, these motorcycles will either be banned, or the owner can apply to be given a temporary permit with usage stipulations, until such time as they are eligible for Classic Vehicle status, which in Singapore is 35 years or older.

The NEA estimates that most of the eligible motorcycles will be able to pass the required emissions standards with proper, regular maintenance. Owners can have their vehicles tested at an approved inspection station to ensure they pass the standards.

The new laws will apply equally to locally owned, as well as foreign motorcycles entering Singapore. Foreign motorcycles must also meet local noise regulations, and must not emit any smoke or visible vapor. Enforcement is planned via random emissions testing blitzes at land entry checkpoints.

For owners of older motorcycles, the NEA is offering an early de-registration incentive of up to $3,500, to encourage owners to get these bikes off the road. According to the NEA, almost 60% of the 27,000 eligible motorcycles have so far been de-registered via this program.

Sources: motopinas.com, http://nea.gov.sg

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Acoustic Treatment in Schools

Several generations of students and teachers have battled the inherent problems caused by noise and poor acoustic design in educational settings. Despite the problem having been recognized for over 100 years, acoustics in classrooms remain under-addressed in older buildings and many newer built schools. A 2012 released study “Essex Study-Optimal classroom acoustics for all” defines the need and benefits of acoustically treating classrooms. The study looked at the impact of reducing reverberation time in a working classroom environment. The conclusion drawn after several measurements of acoustics and surveys with participants was a demonstrable clear benefit to all by improving the acoustic environment. Simply, uncontrolled reverberations in a classroom have a direct negative effect on health and performance, for both students and teachers.

Reverberation is the echo of sound reflecting from hard surface to hard surface causing noise to build up and creating a confusing, unintelligible mass of sound. The hard surfaces such as windows, blackboards, concrete blocks and gypsum walls found in most classrooms do not absorb sound energy and as a result, the sound reflects back into the room, arriving at the ear many times at intervals that are milliseconds apart. This creates a sound that is smeared and the brain has difficulty distinguishing the primary information and disseminating it from the reverberation. This problem is exacerbated when hearing assist devices and cochlear implants are used. Excess reverberation also affects students with auditory processing issues, ADHD, and other learning challenges. In fact, all students benefit from lowering the reverberation and improving intelligibility.

Reverberation is measured in relation to time. The measurement (RT60) is the time it takes for sound to decay by 60dB in a particular space. The greater the reverberation time, the more “echo” in a room, and the greater the listening challenges become. The reverberation time of a room will depend on variables such as the size of the classroom, the reflective surfaces, and how other absorbent or reflective features in the room may increase the effect.


The Effect on Students and Teachers
Most learning occurs from the verbal communication of information and ideas. Traditionally, classrooms have not been designed with attention to how the room sounds or how it may affect the students and teachers that are using it. It is well known that proximity to the teacher increases student engagement and the comprehension of the material being taught. As most classes have 30 or more students in it, it is impossible for every student to be close to the teacher. For students at the rear of the class, the volume level reaching the students will be reduced by as much as 20dB compared to when it is created. The brain then has to differentiate whether the sound being received is the source material or the sound bouncing off the walls. When one factors in the natural reverberation in the room, the delay in sound reaching the ear, along with distractions such as HVAC noise, the classroom base-level sound and noise seeping in from outside the doors and windows, it is not surprising to find that many children are simply not hearing the material they are being taught.
And this is only the beginning. As the ambient sound level in the classroom increases, the teacher naturally increases his or her voice level. The ‘classroom chatter’ naturally increases to compensate and the problem exacerbates to the point where the teacher and students begin to lose concentration.

Children do not Listen Like Adults
When you consider the acoustic problems described, studies suggest that as many as 30% of students may actually be challenged in understanding their teacher’s message. Poor intelligibility due to proximity to the teacher, excessive reverberation and noise result in a lack of comprehension of the material being taught.
Most adults would not notice these challenges as life experience allows us to “fill in the missing words”.

The solution is to acoustically treat the classroom
Right from the early days of radio, broadcasters came to the conclusion that unless the source broadcast was clear and concise, the message would get lost. To address the problem, absorptive acoustic panels were mounted on the broadcast studio wall surfaces to suppress the reflections and improve intelligibility for the listener. This practice continues to this day and the same rules apply whether you are teaching in a classroom, delivering a message in a house of worship or broadcasting a distance learning class over the internet.

A popular solution is to suspend the panels from the ceiling. The added benefit of the airspace created behind the panel when suspended increases the panel’s absorptive surface area. This is particularly effective in noisy cafeterias. For classrooms with T-bar ceilings, there are acoustic tiles that can replace the original non-absorptive compressed fiber tile. Actual panel placement is not as critical as one may think. It is more about using available space to your best advantage by evenly distributing the panels around the room.
A classroom free from excessive reverberation and noise is far more conducive to learning and greatly contributes to better student success – whether the student has learning issues or not. Reducing the ambient sound level also makes it easier to teach, reduces teacher stress and burnout, and significantly reduces listening fatigue for everyone. When you consider the teacher – student benefits and the relatively low cost involved installing acoustic treatment, a practical solution for school districts and post secondary institutions that care about attaining the maximum results from their student body is readily available.

Credit : James Wright, Business development executive at Primacoustic

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Malaysian police conduct noise checks on their own

Malaysian police conduct noise checks on their own

Perhaps in an effort to show the Malaysian public that the law is being applied equally, police conducted motorcycle noise and modification checks on police personnel. The operation was held by the Traffic Investigation and Enforcement Department (JSPT) on police personnel exiting police headquarters at Bukit Aman, Kuala Lumpur.

This was held in response to public sentiment on social media saying the recent over the top police action against motorcycles was only targeted at the riding public. The vehicle examination special op involved 15 officers and 35 other JSPT personnel, accompanied by 5 officers from the police Integrity and Standard department (JIPS), along with personnel from the Department of Environment (DOE).

During the operation, 280 vehicles were inspected, resulting in 146 summons issued for offences such as “fancy” number plates, no side mirrors, no road tax and exhaust modifications. The main objective of this surprise check is to ensure police personnel complied with the law and road rules, showing an example to the public, as stated on the JSPT Facebook page.

Malaysia traffic noise checks

What do you think dear reader, are the police doing the job we pay them to do or is this just mere window dressing and playing to the public gallery? The recent persecution of road users, notable motorcyclists, has reportedly become overbearing and many feel the police are targeting the lower-income and disadvantaged group in these times of pandemic and lockdown with the resulting economic downturn across Malaysia.

While overbearingly noisy exhausts are a nuisance, the current disproportionate response starts to bring to mind images of a police state. 

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Helmholtz Resonator

Resonate absorbers are the most powerful of low-frequency absorption technologies. Pound for pound and square foot per square foot, resonant absorbers can not be matched for low-frequency absorption. They are sometimes called resonance absorbers. We are speaking about real low-frequency absorption which represents all frequencies below 100 Hz. Resonant absorbers are different than other absorbers. They work best in areas of high room sound pressure not high sound velocity areas like porous absorbers that handle middle and high frequencies.

Vibrations & Sound Pressure
A resonant absorber is a vibrational system that “runs” on sound pressure. As vibrational science will tell us a resonant absorber is a mass vibrating against a spring. The mass is the cabinet and front wall or diaphragm. The spring is the air inside the cavity of the resonant absorber. If you change the vibrating mass and stiffness of the spring, you can control and tune the resonant absorber to the resonant frequency of choice. The internal mass or cabinet depth determines design frequency. The spring or internal air and cavity are used for achieving the rate of absorption above the unit’s designed for resonant frequency. There are three types of resonant absorbers: Helmholtz and Diaphragmatic and Membrane.

Helmholtz / Membrane
A Helm resonator is a box or tube with an opening or slot at its mouth. Air enters the slot which has a calculated width, length, and depth. The slot is attached to a cabinet or cylinder of different widths and depths. A glass coke bottle is a good example of a Helmholtz resonator. It is a resonant absorber or as some would term a resonance absorber. The frequency or resonance is determined by the slot dimensions along with the cabinet or cylinder depth. Helms are frequency specific and narrow frequency band coverage. A membrane absorber works similar to a diaphragmatic. It has a membrane than vibrates in sympathy to sound pressure. This vibrating membrane is attached to a cabinet which has a certain depth and fills material. A diaphragmatic absorber works similar to a membrane with more performance per square foot.

 

Calculate Resonant frequency of Helmholtz Slot Absorber

Resonant Frequency Formula
fo = 2160*sqrt(r/((d*1.2*D)*(r+w)))
fo = resonant frequency
r = slot width
d = slat thickness
1.2 = mouth correction
D = cavity depth
w = slat width
2160 = c/(2*PI) but rounded
c = speed of sound in inch/sec
If the gaps vary say 5mm, 10mm, 15mm, 20mm and the wall is angled as shown below, a broad band low mid resonator is created that still keeps the high frequencies alive.

Remember the cavity behind must be airtight!
By working out the different slat widths and slat gaps you can create a broadband low mid resonator at specific frequencies.

Credit : mh-Audio.nl , acousticfields

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Brunei, Sabah: Mystery blast heard, early signs point to sonic boom or meteorite

Mysterious explosion heard in Sipitang, Labuan, Lawas (Sarawak) might originate from a sonic boom high in the skies...

KOTA KINABALU: The mysterious explosion heard by many in Sipitang, Labuan, Lawas (Sarawak), and parts close to these areas on Sunday (Jan 31) could have been a sonic boom or a meteorite which exploded in mid-air.

The Astronomical Society of Brunei Darussalam (PABD) said it received numerous reports from Bruneians who also heard the mysterious loud noise.

The PABD then issued a notice seeking eyewitness accounts of the phenomenon, which is believed to have occurred at about 11 am.

Some Bruneians later shared their experiences and uploaded blurry pictures of what appears to be a fireball trailing smoke to PABD’s Facebook page.

A Sabahan in Brunei, Joey Yong, said she heard something like extremely loud thunder but did not know what it was.

The accounts from these witnesses may be found here.

Earlier, authorities in Sabah, including the navy, police and fire brigade, said they did not receive reports of any incidents that could have caused the blast.

Sabah Meteorological Department director Amir Zudi Hashim said the department did not record any seismic activity that could have caused the sound.

Sonic boom cause of explosion like noise Sabah

 

People in Sabah who claimed to have heard the blast said they felt the earth shake when the explosion was heard.

Source