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Noise Nuisance Monitoring Thailand, Malaysia, Indonesia, Vietnam
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.
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
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!
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”.
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.
Noise Nuisance Monitoring Thailand, Malaysia, Indonesia, Vietnam
