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Asia Noise News Building Accoustics

Railway Noise

Rail transport or train transport is one of the main transportation modes these days, both for transferring passengers and goods. Every day people commute to work and back home using trains in a form of subway systems, light rail transits and other types of rail transport. These types of system can create noise both to the passengers inside of the train as well as to the environment. In this article, we will discuss about noise source components that we hear daily both inside and outside of the train.

If we pay attention to the noise when we are on board of a train, there are more than one noise source that we can hear. The main sources for interior noise in a train are turbulent boundary layer, air conditioning noise, engine/auxiliary equipment, rolling noise and aerodynamic noise from bogie, as illustrated in the following figure.

By the way, we wrote and recorded the sound of Jakarta MRT. You can see the link below to help you imagine the train situation better.

Exploring Jakartan Public Transportation Through The Sound

Rolling noise is caused by wheel and rail vibrations induced at the wheel/rain contact and is one of the most important components in railway noise. This type of noise depends on both wheel and rail’s roughness. The rougher the surface of both components will create higher noise level both inside and outside of the train. To be able to estimate the airborne component from the rolling noise, we must consider wheel and track characteristics and roughness.

Another noise component that contributes a lot to railway noise is aerodynamic noise which can be caused by more than one sources. These types of sources may contribute differently to internal noise and external noise. For example, aerodynamic noise contributes quite significantly at lower speeds to internal noise while for external noise, it doesn’t contribute as much if the train speed is relatively low. For example, on the report written by Federal Railroad Administration (US Department of Transportation), it is stated that aerodynamic sources start to generate significant noise at speeds of approximately 180 mph (around 290 km/h). Below that speed, only rolling noise and propulsion/machinery noise is taken into consideration for external noise calculation. In addition to external noise, machinery noise also contributes to the interior noise levels. This category includes engines, electric motors, air-conditioning equipment, and so on. 

To perform the measurements of railway noise, there are several procedures that are commonly followed. For measurement of train pass-by noise, ISO 3095 Acoustics – Railway applications – measurement of noise emitted by rail bound vehicles, is commonly used. This standard has 3 editions with the first published in 1975, and then modified and approved in 2005 and again in 2013. The commonly used measures for train pass-by are Maximum Level (LAmax), Sound Exposure Level (SEL) and Transit Exposure Level (TEL).

For interior noise, the commonly used test procedure is specified in ISO 3381 Railway applications – Acoustics – Measurement of noise inside rail bound vehicles. This procedure specifies measurements in few different conditions such as measurement on trains with constant speed, accelerating trains from standstill, decelerating vehicles, and stationary vehicles. 

Written by:

Hizkia Natanael

Acoustical Design Engineer

Geonoise Indonesia

hizkia@geonoise.asia

Reference:

D. J. Thompson. Railway noise and vibration: mechanisms, modelling and means of control. Elsevier, Amsterdam, 2008

Federal Railroad Administration – U.S. Department of Transportation, High-Speed Ground Transportation Noise and Vibration Impact Assessment. DOT/FRA/ORD-12/15. 2012

Categories
Asia Noise News

Noise, Nuisance or Danger

As an introduction to this question some basic facts about noise.

Basic noise facts

Noise is typically defined as ‘unwanted sound’. The unit for sound is the Decibel which is a value calculated with logarithms from the pressure to get a scale from 0 to 120 dB where 0 dB is the hearing threshold for a young person with healthy hearing and 120 dB is the pain threshold.

We can state that noise is a type of energy created by vibrations. When an object vibrates it causes moment in air particles. The particles will bump into each other and will generate sound waves, they are ongoing until they run out of energy.

High and low tones are perceived by our hearing due to fast and slow vibrations.

Sound needs a medium to travel and the speed of sound is around 340 meter per second. Examples of typical noise levels:

Due to the nature of the calculation of Decibels we cannot just add them together.

Examples:

3 dB + 3 dB = 6 dB

But…..

10 dB + 10 dB is not 20 dB but 13 dB

The Decibel (sound pressure level) for sound in air is relative to 20 micro pascals (μPa) = 2×10−5 Pa, the quietest sound a human can hear.

The human hearing system

The human hearing system is capable of hearing sounds between 20 Hz and 20000 Hz. Below 20 Hz is called infra sound and above 20000 Hz is called ultrasounds. Both infra- and ultrasound is not audible for us. Elephants however can hear frequencies as low as 14 Hz and bats can hear frequencies up to 80000 Hz.

A special noise weighting for the human perception has been introduced in the 1930’s and called the A-weighted Decibel, dB(A). This was introduced to align the noise levels with the sensitivity and physical shape of the human hearing system.

Basic human hearing system

When sound waves enter the ear, they travel up the ear canal and hit the ear drum, the ear drum will vibrate and the three smallest bones in the human body will transfer these vibrations to the fluid in our inner ear’s sensory organ the cochlea. The sensory hair cells will vibrate which will send nerve impulses to the brain, the brain will translate these impulses for us and we perceive sound!

Dangers of noise

Noise from certain music can be a very pleasurable sound for one person and a horrific noise for another. From this fact we can see that noise is not only an absolute value but also strongly depending on the receiver’s mindset.

However, there are some clear absolute values concerning the danger levels of noise.

  • Generally accepted as safe is spending 8 hours per day in an environment not exceeding 80 dB(A)
  • NOT safe would be to spend 1 hour in a disco with levels at 100 dB(A) which are easily exceed nowadays

Apart from the obvious hearing loss there are many other issues that can arise from exposure to (too) high noise levels such as:

  • Hypertension
  • Heart disease
  • Annoyance – stress
  • Immune system – psychosomatic

The positive side to remember is that Noise Induced hearing loss is 100% preventable!!

Worldwide solutions

Governments (especially in Europe) know the actual cost of high noise exposure and they concluded that protecting their citizens from high noise exposure (during working hours, recreation as well as during sleep) is far more effective than dealing with the costs of citizens enduring high noise related illnesses, demotivation, sleep disturbance etc.

They are investing in quiet schools (optimal learning environment), quiet hospitals (patients recover a lot faster in quiet wards), implement city planning to create quite zones.

Of course, they also have strong noise regulations that are being enforced.

Acoustical societies worldwide help to create awareness and leverage noise legislations with governments.

Noise in Asia

I have been living in Asia for the last 15 years and of course I noticed it’s noisy. Noise regulations (if exist at all) are very lenient and mostly not enforced. I’m very happy to see that Acoustical Societies are coming up in Asian countries and can convince governments to invest in setting up proper noise regulations and enforcing them. I’m very happy to be able to contribute to a quieter world by creating more awareness for the dangers of noise!

Categories
Building Accoustics

Researchers Develop ‘Acoustic Metamaterial’

Boston University researchers, Xin Zhang, a professor at the College of Engineering, and Reza Ghaffarivardavagh, a Ph.D. student in the Department of Mechanical Engineering, released a paper in Physical Review B demonstrating it’s possible to silence noise using an open, ring-like structure, created to mathematically perfect specifications, for cutting out sounds while maintaining airflow.

They calculated the dimensions and specifications that the metamaterial would need to have in order to interfere with the transmitted sound waves, preventing sound—but not air—from being radiated through the open structure. The basic premise is that the metamaterial needs to be shaped in such a way that it sends incoming sounds back to where they came from, they say.

As a test case, they decided to create a structure that could silence sound from a loudspeaker. Based on their calculations, they modeled the physical dimensions that would most effectively silence noises. Bringing those models to life, they used 3-D printing to materialize an open, noise-canceling structure made of plastic.

Trying it out in the lab, the researchers sealed the loudspeaker into one end of a PVC pipe. On the other end, the tailor-made acoustic metamaterial was fastened into the opening. With the hit of the play button, the experimental loudspeaker set-up came oh-so-quietly to life in the lab. Standing in the room, based on your sense of hearing alone, you’d never know that the loudspeaker was blasting an irritatingly high-pitched note. If, however, you peered into the PVC pipe, you would see the loudspeaker’s subwoofers thrumming away.

The metamaterial, ringing around the internal perimeter of the pipe’s mouth, worked like a mute button incarnate until the moment when Ghaffarivardavagh reached down and pulled it free. The lab suddenly echoed with the screeching of the loudspeaker’s tune.

How acoustic metamaterial works – Geonoise Instruments
How acoustic metamaterial works – Geonoise Instruments

Now that their prototype has proved so effective, the researchers have some big ideas about how their acoustic-silencing metamaterial could go to work making the real world quieter.

Closer to home—or the office—fans and HVAC systems could benefit from acoustic metamaterials that render them silent yet still enable hot or cold air to be circulated unencumbered throughout a building.

Ghaffarivardavagh and Zhang also point to the unsightliness of the sound barriers used today to reduce noise pollution from traffic and see room for an aesthetic upgrade. “Our structure is super lightweight, open, and beautiful. Each piece could be used as a tile or brick to scale up and build a sound-canceling, permeable wall,” they say.

The shape of acoustic-silencing metamaterials, based on their method, is also completely customizable, Ghaffarivardavagh says. The outer part doesn’t need to be a round ring shape in order to function.

“We can design the outer shape as a cube or hexagon, anything really,” he says. “When we want to create a wall, we will go to a hexagonal shape” that can fit together like an open-air honeycomb structure.

Such walls could help contain many types of noises. Even those from the intense vibrations of an MRI machine, Zhang says.

According to Stephan Anderson, a professor of radiology at BU School of Medicine and a coauthor of the study, the acoustic metamaterial could potentially be scaled “to fit inside the central bore of an MRI machine,” shielding patients from the sound during the imaging process.

Zhang says the possibilities are endless, since the noise mitigation method can be customized to suit nearly any environment: “The idea is that we can now mathematically design an object that can block the sounds of anything”.

Source:

https://phys.org/news/2019-03-acoustic-metamaterial-cancels.html

Categories
Asia Noise News Building Accoustics

Noise and Vibration Monitoring for Construction Sites

In a densely populated city like Bangkok, most of the construction projects are surrounded by condominiums, offices or residential areas. The construction sites must control the noise and vibration that may affect the surroundings. Construction sites need to control the noise and vibration levels that they produce following the EIA standard.

To manage this, noise and vibration instruments are installed which automatically will send alarms to the construction company if the thresholds are exceeded.

Noise Monitoring Station

Sound level meter class 2 according to IEC61672-1 standard which can collect the data of SPL, LEQ and LMAX. These instruments are calibrated before they are installed at a construction site. The system has a LED display and warning light when noise levels in the site are over a trigger level, which is referred to in the standards for maximum sound levels around construction sites.

According to the announcement of National Environment Board no.15 BE.2540 (1997) in the topic of “Standard loudness”, the average sound 24 hour must not exceed 70 dBA and the maximum peak level must not exceed 115 dBA.

Sound level meter are designed to be used outdoors and an additional LED display was added by Geonoise which is a professional sound and vibration company. Sound level meter with LED display also can analyse the loudness in percentile (Statistical,Ln) or analyse the frequencies in 1/1 and 1/3 octave bands. In addition to storing vibration data, you can also create level notifications in Alarm Alert format before vibration levels exceed the standard value for monitoring the activities being performed.

Vibration Monitoring

In the construction industry, transportation Industry and most large industries vibrations will occur.
High vibration levels will cause structural damage to buildings, bridges, structures as well as nuisance or health risks to occupants in exposed (residential) buildings.

Therefore, it is necessary to comply with the standard of vibration in a building according to the Announcement of the National Environment Board Announcement No. 37, BE 2553 (2010) Re: Determination of Standard Vibration to Prevent Impact on Buildings and the measuring instruments need to comply with DIN45699-1.

At construction projects in Bangkok, most cause a lot of unwanted noise and vibrations. Vibration caused by construction projects are caused by piling work as well as the increased traffic of large trucks that enter and exit the construction site. To prevent that vibration levels will be exceeded, a vibration monitoring system will have to be installed.

The Announcement of the National Environment Board No. 37, BE 2553 Vibration standards to prevent impacts on buildings is the main regulation to comply with for construction sites in Thailand. The vibration standards are derived from DIN 4150-3 whereas buildings are classified into 3 types.

Building types according to DIN 4150-3:

  • Type 1 buildings such as commercial buildings, public buildings, large buildings, etc.
  • Type 2 buildings such as residential buildings, dormitories, hospitals, educational institutions, etc.
  • Type 3 buildings, such as archaeological sites or buildings that cultural values but not strong, etc.

In addition to storing vibration data, you can also create level notifications in Alarm Alert format before vibration level exceed the standard value for monitoring the activities being performed.

Categories
Asia Noise News

Studies have shown a relationship between noise and increased risk of hypertension, heart attack and angina.

Studies have shown a relationship between noise and increased risk of hypertension, heart attack and angina.

Mathias Basner, a scientist dedicated to the study of noise in a lecture on TEDMED talks about how noise affects health and sleep people, reports the online edition of the Chronicle.info with reference for a New time.

In our day, silence is a rare pleasure, and the price is our health. Surprisingly high price, as it turned out. Fortunately, we have things to do today — each of us personally and society in General — to better protect your health and enjoy the benefits of silence.

I assume most of you know: the high level of noise leads to hearing loss. Whether you go with a concert or bar, if you experience ringing in the ears, you can be sure that you already have damaged hearing and, most likely, it is irreversible. Hearing loss is no joke. However, the noise is damaging our health in other ways. They are not well known, but just as dangerous as impaired hearing.

So what do we mean when we speak about noise? Noise is defined as unwanted sound, which includes the physical component, that is, the sound as such, and the physiological component — the circumstances that make this undesirable sound. A good example is a rock concert. The spectators who came to the rock concert does not consider the performance of musicians noise even with the volume at 100 decibels. They enjoy the music and even pay a hundred dollars for a ticket, so whatever loud music may be, they do not perceive it as noise.

For comparison, someone living three blocks from the concert hall, trying to read a book but can’t focus because of the music. Although the sound pressure in this situation is much lower, people perceive this music as noise that can provoke a reaction, which over time will adversely affect his health.

So why is it so important to be able to enjoy the silence? Because, in addition to hearing loss, the noise has an impact on human health overall. However, in our time is becoming increasingly difficult to find a quiet place in view of the constantly increasing number of vehicles, urbanization, unfolding construction, air conditioners, machines for harvesting leaves, lawn mowers, outdoor concerts and bars, players and neighbours having parties till three in the morning.

In 2011, the world health organization estimated that each year in Western Europe due to noise pollution lost 1.6 million healthy years of life. One of the results of noise impact is the creation of communication barriers. You have to speak louder to be understood. In the worst case, may even be necessary to interrupt communication. In a noisy environment, the probability that it will be misinterpreted. This is a possible explanation for why the children attending schools in noisy areas, academic achievement lower than their peers, as evidenced by the conducted research.

Another result of the impact of noise on the body is the increased risk of cardiovascular disease in people exposed to certain noise levels over a long period of time. Noise causes stress, especially if we are not able to control it. Our body produces stress hormones such as adrenaline and cortisol, which alters the composition of the blood, as well as the structure of blood vessel walls, which become less elastic in just one night in a noisy room.

Epidemiological studies have shown a relationship between noise and increased risk of hypertension, heart attack and angina. And despite the fact that this risk accumulates in small doses, it poses a great problem for public health because the noise is everywhere, and he affected many of us.

A recent study showed that reducing the noise pollution of the environment by only five decibels, Americans annually would save $3.9 billion, which today are spent on the treatment of cardiovascular diseases. There are other diseases, such as cancer, diabetes and obesity, which are also associated with the influence of noise, but we do not yet have sufficient evidence that the noise is the cause of their development.

Another important consequence of noise pollution is sleep disturbance. Sleep is an active mechanism for the body, it prepares us for the next phase of wakefulness. The silence in the bedroom is the key to what researchers call “hygiene healthy sleep”. And our auditory system is the guard, which carries out constant monitoring of the external environment, identifying potential threats, even when we sleep. Therefore, the noise in the bedroom prevents to fall asleep quickly.

Because of the noise, we can Wake up in the night. It can also prevent the normalization of blood pressure during sleep. There is an assumption that if the result of the noise a person experiences insomnia for several months and even years, the risk of cardiovascular disease increases. However, often we are not aware of the sleep disturbances caused by noise, because during sleep a person is unconscious.

We conducted a study of the impact on sleep traffic noise. Waking up in the morning, many of the subjects told us: “I slept great, once fell asleep and never woke up”. But when we looked at made during sleep recording physiological reactions of subjects, we saw that they woke up and their sleep was very intermittent. These periods of wakefulness was too short so that the subjects were awake and in the morning nothing of them remembered. However, these periods can significantly affect how relaxed people feel after sleep.

So what sounds are considered too loud? The first sign is that you have to change their behaviour. To be understood you have to speak louder. Or you turn on the TV on high volume, avoid being outdoors or close the Windows, moving the bedroom on the ground floor of the house or even installing insulation. A move to less noisy areas but, of course, not everyone can afford it.

What can we do right now to improve our sound environment and protect the health? First, if you think some sounds are too loud, do not be silent about it. Many theatre owners seem to think that in the movie, just go deaf. If you complained about the noise, but there was no response, ask for a refund or leave it. This language, as a rule, administrators know very well.

Also explain to children that noise affects health and what if now they will listen to loud music, then in older age they will have to reap the rewards.

You can also move the bedroom in the quietest place in the house: the noise of street transportation you will protect the walls of your home. Seeking rental or purchase of housing, give preference to locations that are in quiet areas. Visit the place of your future residence at different times of the day, ask neighbours about how noisy things are in this area.

Wear noise-cancelling headphones while travelling or in the office, if your building a high level of background noise. In General, looking for a quiet place, especially at weekends or during the holidays. Let your body relax.

By the way, four years ago, I visited Japan for a conference on the issues of noise pollution. When I returned to the United States, already at the airport I covered the sound wave. This suggests that we have ceased to realize that are constantly subjected to noise pollution and what value we are a quiet space.

What else can you do? There is such a thing as a carbon footprint. By analogy, there is a noise trace. And there are things we can do to make this footprint smaller. For example, it is not necessary to mow the lawn on Saturday at seven in the morning. Your neighbours will say thank you for it. Or use a rake instead of a blower. In General, it is most reasonable to limit the noise at its very source, so when you are going to buy a new car, air conditioning, blender, or something else, give preference to those models that create less noise. Many manufacturers indicate the level of noise generated by their merchandise, and some even advertise it. Take advantage of this information.

Many believe that the solution is to strengthen the regulation and control of noise, considering it obvious. But not so simple as it seems because many of the activities that create noise, are also a source of profit. Take, for example, the airport and everything to do with his work. Thanks to our ongoing research policy, find out what level of noise can adversely affect health, allowing them to develop reasonable measures to reduce noise.

Robert Koch is credited with saying: “someday man will have for its existence as hard to deal with the noise, as he struggles now with cholera and the plague”. I think this moment has come, and I hope that we will win this fight. And when that happens, we quietly celebrate our victory.

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