Tác giả: Michel

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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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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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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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Sound Absorption

What is Absorption?

Absorption refers to the process by which a material, structure, or object takes in energy when waves are encountered, as opposed to reflecting the energy. Part of the absorbed energy is transformed into heat and part is transmitted through the absorbing body. The energy transformed into heat is said to have been ‘lost’. (e.g. spring, damper etc.)

 

What is Sound Absorption?

When the sound waves encounter the surface of the material: part of them reflects; part of them penetrate, and the rest are absorbed by the material itself.

Formula for Sound Absorption: –

The ratio of absorbed sound energy (E) to incident sound energy (Eo) is called sound absorption coefficient (α). This ratio is the main indicator used to evaluate the sound-absorbing property of the material. A formula can be used to demonstrate this.

 

α (absorption coefficient) =E (absorbed sound energy)/ Eo (Incident sound energy)

 

In this formula: α is the sound absorption coefficient;

  E is the absorbed sound energy (including the permeating part);

  Eo is the incident sound energy.

 

Generally, the sound absorption coefficient of the materials is between 0 to 1. The larger the numeral is, the better the sound absorbing property. The sound absorption coefficient of suspended absorber may be more than one because its effective sound-absorbing area is larger than its calculated area.

 

Example: If a wall is absorbed 63% of incident energy and 37% of energy is reflected then the absorption coefficient of wall is 0.63.

 

How can we measure Absorption Coefficient?

 

The absorption coefficient and impedance are determined by two different methods according to the type of incident wave field.

 

  1. Kundt’s tube (ISO 10534-2)
  2. Reverberation room (ISO 354)

 

Kundt’s Tube Measurement Method: (ISO 10543-2)

For measurement of small specimen use Kundt’s tube or Impedance tube also called as Standing wave tube.  The result from measurement of absorption factor and acoustic impedance, using the standing wave method, obviously are meaningful only when assuming these to be independent of the size of the specimen, which is normally quite small.  The absorption factor for normal incidence is determined by measuring the measuring the maximum and minimum pressure amplitude in the standing wave set up in the tube by a loudspeaker. 

This basic technique is, an mentioned in the introduction, considered a little outdated in comparison with more modern methods based on transfer was implemented relatively late (1993) in an international standard, ISO 10534-1, after being used for al least 50 years.  Commercial equipment has also been available for many decades.  However, there exists a second part of the mentioned standard, ISO 10534-2, based on using broadband signals and measurement of the pressure transfer function between different positions in the tube.  ISO 10543-2, which implies the specified two microphone method is extended to spherical wave fields.

Normally Placid Impedance tube is used for absorption coefficient and transmission loss measurement. 

(https://www.placidinstruments.com/product/impedance-tube/)

The above fig shows Impedance tube

 

Click here to refer Placid Sound absorption measurement  

Click here to refer Placid Sound transmission loss measurement

 

 

Reverberation Room: (ISO 354)

 

              Reverberation Room method is traditional method, measurement of the absorption factor of larger specimens is performed in a reverberation room.  One then determines the average value over all angles of incidence under diffuse field conditions.  The product data normally supplied by producers of absorbers are determined according to the international standard ISO 354, required for measurement is 10-12 square meters and there are requirements as to shape of the area.  The reason of these requirements is that the absorption factor determined this method always includes an additional amount due to the edge effect, which is a diffraction phenomenon along the edge of the specimen.  This effect makes the specimen acoustically larger the geometric area, which may result in obtaining absorption factors larger than 1.0.  Certainly, this does not imply that the energy absorbed is larger than the incident energy.

 

 

Sound Absorption coefficient of different materials:

The sound absorption of the material is not only related to its other properties, its thickness, and the surface conditions (the air layer and thickness), but also related to the incident angle and frequency of the sound waves. The sound absorption coefficient will change according to high, middle, and low frequencies. In order to reflect the sound-absorbing property of one material comprehensively, six frequencies (125Hz, 250Hz, 500Hz, 1000Hz, 2000Hz, 4000Hz) are set to show the changes of the sound absorption coefficient. If the average ratio of the six frequencies is more than 0.2, the material can be classified as sound-absorbing material.

Application of Sound Absorber:

These materials can be used for sound insulation of walls, floors, and ceilings of concert hall, cinema, auditorium, and broadcasting studio. By using the sound absorbing material properly, the indoor transmittance of sound waves can be enhanced to create better sound effects.

Select your sound absorber from https://www.blast-block.com/

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Industrial

Hotel Room Acoustics – how noise affects a person’s stay in the hotel

Hotel Room Acoustics – how noise affects a person’s stay in the hotel

Hotels have been playing an important role during the current pandemic. In certain countries, the local governments have announced that it is compulsory for those entering the country from overseas to carry out hotel quarantine. Taking Malaysia as an example, travellers entering the country regardless from any country are required to undergo hotel quarantine for up to 10 days (as of January 2021), in which the local authorities will arrange the rooms for them unless the travellers opted for Premium Package which of course, costs higher than the standard ones. Travellers will have to take COVID tests in between to ensure that they are COVID-negative and isolating them in the hotels will make sure that there will not be the possibility of spreading the virus to the public since all travellers should be taken as potential risk carrier.

Hotel room comfort

Many may be wondering: How is the cleanliness of the room? Are the meals provided good? What about the Wi-Fi strength there?

But there is one thing that people sometimes forget about: Noise. From the study done by the J.D. Power North American Hotel Guest Satisfaction Survey, it has been consistently shown that complaints on noise issues are significantly under-reported, and hardly being resolved in the end (Simonsen, 2019). Imagine living in a confined space for more than 10 days, where you need to experience constant noise coming from your neighbours, or from outside the room like traffic or construction noise, how will you feel? Looking at some hotel review posts in the Malaysia Quarantine Support Group (MQSG) created to aid travellers coming into Malaysia, there seem to be numerous posts complaining about noise nuisance during their quarantine period. The typical problems faced by members include:

  1. Traffic noise – hotel is located next to busy road
  2. Construction noise in the day from nearby sites
  3. Loud neighbours – speaking loudly especially at sleeping hours

To be exact, these are the similar nuisance one would experience in residential houses.

For short term stays, these may not be the main concern, but it is a totally different case for a quarantine. Unreasonable amount of noise daily for long term, especially after a tired flight and transition at the airport, will lead to unwanted circumstances on a person’s health (physically and mentally).

Noise and Sleep Disturbance

For people who are extremely sensitive to noise, the first thing that can be observed will be that they cannot sleep or even rest well. This will result in sleep deficiency, which slowly drains off the energy to carry out daily tasks. According to Hume, many from the research field claimed that sleep disturbance caused by environmental noise has the most detrimental effect to health. Having an undisturbed night of sleep is even taken to be a fundamental rights and prerequisite to ensure continued health and well-being (Hume, 2010). Hume mentioned that noise pollution can be described as the “modern unseen plague” which may interfere with cognitive processes hence disturbing sleep quality.

To overcome the problem of noise affecting sleep quality, the World Health Organization (WHO – European Office) has brought in experts with relevant documents in recent years to establish the Night Noise Guidelines for Europe. The guidelines contain the latest reviews of noise disturbance and the potential risk to human health. Below are the four ranges of continuous external sound level at night, relating night noise and the populations’ health effects:

<30 dB – no substantial biological effects could normally be expected

30-40 dB – primary effects on sleep start to emerge and adverse effects in vulnerable groups

40-55 dB – sharp increase in adverse health effects while vulnerable groups become severely affected

>55dB – adverse health effects occur frequently with high percentage of the population highly annoyed

These guidelines help to understand the effect of noise on sleep, although a large extent of this topic still relies on fully understanding the fundamentals of the nature of sleep.

Acoustics Solutions for Hotels

As mentioned in the previous sections, the noise complaints for hotel rooms mainly cover traffic noise, noise from neighbours and construction noise. Since sound travels in wave forms, soundproofing will be one of the best concepts to act as a barrier that can effectively stop the sound waves from entering a room from outside.

Typically, there are four methods to achieve the soundproofing effect for hotel rooms (SoundGuard, 2019):

  • Absorption – adding sound insulating materials such as mineral wool or fiberglass for sound absorption, thus preventing sound from passing through
  • Damping – soundwaves often cause vibrations between air particles. Damping helps in reducing or eliminating the vibrational effects by acting as a barrier that does not vibrate
  • Decoupling – In layman terms, this also means separating the walls by adding an insulation layer between the two layers of drywall.
  • Mass – Utilizing thicker, heavier, or denser materials to block sound

While choosing the right material for insulation, it is important to take note on the Sound Transmission Class (STC) rating. The STC rating defines the effectiveness of materials in attenuating airborne sound. The lower the STC rating, the less sound that can be effectively blocked. Therefore, to achieve good insulation results, it is better to use a material with higher STC value.

When should you implement acoustical solutions?

Ideally, it is best to start from the very beginning, which is during the project planning stage (yes, before you even start building it!). Quoting a line said by Scott Rosenberg, the president of Jonathan Nehmer + Associates, and the principal with HVS Design, “You have to think about the inside walls like they’re on the outside” (Fox, 2018). This was said for atrium style hotels which are normally structured like giant echo chambers, where noise from the lobby may travel up to the penthouse suite due to the structure. In the planning stage, allocating which part of the hotel goes where is also crucial to make sure you keep sounds in the right places, and nowhere else. For example, it is important to locate the facilities like gyms, pub, or even spa strategically so that the noise from these places will not affect the guests staying in the hotel rooms. If you really must put them above/below rooms, make sure to use walls or ceilings that are properly insulated.
For existing hotels, another good time to improve the acoustics of the hotel will be during renovation periods. Since you took the step to upgrade your hotel looks and structure, why not consider soundproofing as well? It will definitely help to raise the customers’ satisfaction during their stay.
The areas that can be considered for hotel soundproofing during renovation include:
• Floors – adding soundproofing underlay
• Ceilings – using decoupling methods (dual-layered drywall)
• Doors – changing to solid-core heavy doors with seals
• Walls – adding insulation between walls / use soundproofing paint

 

How do you know if your hotel needs acoustical improvements?

Although some may only start treating the problem after getting significant complaints from customers, hotel owners should consider taking the initiative to find out the noise condition in the building. A good start will be to carry out noise measurement tests to monitor the condition in each room. Having noise data from the measurements will help you understand what the situation is, and how you should resolve them. This is where an acoustics consultant should step in.
It is suggested to consult the acoustics specialists to get the most suitable solution for your case, because not all solutions can be applicable for all conditions. Acoustics consultants can help you to analyse the condition by using methods like indoor noise mapping, material insulation calculations and even tiny suggestions like adding certain types of furniture to aid sound absorption in the room itself.


Effects of Acoustics Improvement to the Hotel

It is proven that by enhancing the acoustics of hotels, business can be improved too. For example, Premier Inn in the UK has pioneered the new design of “floating bedroom” in 2011 at its hotel in Leicester Square. This new design allowed the hotel to resolve the environmental noise and the noise coming up from the nightclub on the ground floor. Premier Inn had also changed their focus from cost to customers’ sleep quality, which enabled them to become one of the best-rated hotels in London (Simonsen, 2019). Thus, the hotels’ business and reputation will strongly improve by taking care of the noise aspects.
Now, back to the starting topic of this article. Hotels are no longer only used as the accommodations for vacations or business trips. Hotels play an important part during this pandemic, being the quarantine centres in many countries. Therefore, it is important to ensure the customers’ (or those under quarantine) comfort during their stay, voluntarily or not. Their reviews make a lot of difference, which will highly impact a hotel’s image to the public. Most importantly, good, soundproofed room means less noise, resulting in better living and sleep quality. Hence, hotel owners are urged to investigate the acoustics aspects of their property, for themselves, and for the customers.


References

Fox, J. T. (2018, July 17). Careful hotel design keeps noise in check. Retrieved February 4, 2021, from Hotel Management: https://www.hotelmanagement.net/design/careful-hotel-design-keeps-noise-check


Hume, K. (2010). Sleep disturbance due to noise: Current issues and future research. Noise Health, 12(47), 70-76. Retrieved February 2, 2021, from https://www.noiseandhealth.org/article.asp?issn=1463-1741;year=2010;volume=12;issue=47;spage=70;epage=76;aulast=Hume


Simonsen, J. (2019, June 20). Why and how to reduce noise in hotel rooms. Retrieved February 3, 2021, from Rockwool: https://www.rockwool.com/group/advice-and-inspiration/blog/why-and-how-to-reduce-noise-in-hotel-rooms/


SoundGuard. (2019). Hotel Sound Reduction – How to Soundproof a Hotel Room. Retrieved February 3, 2021, from SoundGuard: https://soundguard.io/hotel-sound-reduction-soundproof-hotel-room/

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Asia Noise News Environment

Noise in Malaysia

What Covid-19 did to Malaysia

2020 has been a year full of ups and downs. One big thing that affected, in fact, is still affecting the whole world is undeniably the Covid-19 pandemic. No doubt that the pandemic has caused a lot of downhills in the development of many aspects, like economy and social, but there is one thing that have shown obvious positive sign during this situation: the environmental change.

Figure 1 A picture showing the clearer skies in Kuala Lumpur, the capital of Malaysia (Photos: Filepic).

According to a Malaysian news report by Ming Teoh from The Star, the movement control order (MCO) that was carried out to tackle the Covid-19 spread in Malaysia has brought positive environmental impacts to the country (Teoh, 2020). People were amazed by the clean rivers, clear blue skies and the recovery of nature and wildlife. Of course, due to the MCO where a lot of human activities were restricted, the streets and urban roads have been very quiet as compared to the usual noise level. The improved noise quality resulted in lower noise pollution, which made the sounds of the fauna more apparent. But once everyone gets back to normal life when the MCO is lifted, how long can this positive environmental situation last? Will there be enough time for the environment to heal properly?

The Department of Environment (DOE), Ministry of Energy, Science, Technology, Environment and Climate Change (MESTECC), Malaysia

The Department of Environment (DOE) from the Ministry of Energy, Science, Technology, Environment and Climate Change (MESTECC) of Malaysia have been very concerned about this issue all the while, specifically on the noise quality of the country. They have constantly been updating the guidelines to handle noise or vibration for various applications, for example vehicle-noise, ambient noise, or outdoor noise sources in the environment. In one of the published guidelines for environmental noise limits and control (2009), the DOE have specified a table showing the permissible sound levels for different applications, shown in Table 1 as one of the examples from the guidelines (Air & Noise, 2019). 

Table 1 An example of the permissible sound levels listed in the guidelines published by the DOE.

The permissible sound levels differ by the applications (i.e. use of land, human density) and the different times of the day, to ensure that the circumstances of various conditions are taken into account during the sound level measurements. For instance, the ambient noise limits are set such that it is an absolute limit based on the average level of noise (which should not be exceeded in a specified period), or in accordance with a relative limit based on the permitted increase in noise level with respect to the background level. It is mentioned that the limits should always be consistent with the environmental noise climate of the location. The rest of the noise limit schedules listed in the guidelines include those for land use, road traffic, railway/transit trains, construction, and maintenance, which are the main sources of outdoor noise in the country. 

Besides that, the report also covers guidelines on planning process, noise impact assessments, quantifying of noise disturbance, and guidance in environmental noise mitigation through planning and control. These are ideally applied in new and existing projects planning, in which the projects can cover anything that involves noise, as a potential concern or needed to be measured and assessed. This is a very imperative measure from the DOE to enforce noise control in the country to work on controlling the noise impact of the relevant applications, thus overcoming the noise pollution in Malaysia. With these actions being taken and followed, the goal to maintaining a better noise quality in the country can be achieved in near future.

Written by:

Khei Yinn Seow

Mechanical Engineer

Geonoise Malaysia

khei@geonoise.asia 

References:

Air & Noise, P. S. C. S., 2019. Guidelines for Environmental Noise Limits and Control (Third Edition), Putrajaya: Department of Environment Malaysia.

Teoh, M., 2020. Blue skies, less waste: Covid-19 and the MCO’s effects on the environment., s.l.: The Star.

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Building Acoustics Industrial Vibration

Baku Getaran pada Bangunan

Berbagai kegiatan dan usaha manusia dapat mengganggu lingkungan sekitarnya karena getaran (vibrasi) yang ditimbulkan. Misalkan saja konstruksi (contohnya pada saat pekerjaan pemancangan), pertambangan, dan lain sebagainya. Getaran tersebut dapat mengganggu kenyamanan dan kesehatan penghuni di sekitarnya, dan bahkan dapat menimbulkan dampak kerusakan pada bangunan di sekitarnya.

Di Indonesia, baku tingkat getaran diatur melalui Keputusan Menteri Negara Lingkungan Hidup No. 49 Tahun 1996. Peraturan ini dibuat untuk menjamin kelestarian lingkungan hidup untuk manusia dan makhluk hidup lainnya. Oleh karena itulah dampak dari usaha atau kegiatan yang dapat mengganggu Kesehatan manusia, makhluk lain dan lingkungan akibat getaran perlu diatur dan pengendalian pencemaran dan perusakan lingkungan, dalam hal ini terkait getaran, perlu diatur.

Pada peraturan tersebut, penanggung jawab usaha atau kegiatan wajib untuk:

  1. Mentaati baku tingkat getaran yang telah dipersyaratkan. Kewajiban ini dicantumkan dalam izin yang relevan untuk mengendalikan tingkat getaran bagi setiap usaha atau kegiatan yang bersangkutan
  2. Memasang alat pencegahan terjadinya getaran
  3. Menyampaikan laporan hasil pemantauan tingkat getaran sekurang-kurangnya 3 (tiga) bulan sekali kepada Gubernur, Menteri, Instansi yang bertanggung jawab di bidang pengendalian dampak lingkungan dan instansi teknis yang membidangi kegiatan yang bersangkutan serta instansi lain yang dipandang perlu.

Baku tingkat getaran sendiri dibagi menjadi beberapa bagian yaitu:

  1. Baku tingkat getaran untuk kenyamanan dan Kesehatan
  2. Baku tingkat getaran mekanik berdasarkan dampak kerusakan
  3. Baku tingkat getaran mekanik berdasarkan jenis bangunan
  4. Baku tingkat getaran kejut

Tabel dan grafik berikut adalah baku tingkat getaran untuk kenyamanan dan kesehatan:

Seperti terlihat pada tabel, nilai tingkat getaran dibagi menjadi Diizinkan, Mengganggu, Tidak nyaman dan Menyakitkan:

Tabel berikut digunakan untuk baku tingkat getaran mekanik berdasarkan dampak kerusakan:

Seperti dapat dilihat ditabel, batas gerakan peak dari getaran dibagi menjadi 4 kategori yaitu:

  • Kategori A: tidak menimbulkan kerusakan
  • Kategori B: Kemungkinan keretakan plesteran (retak/terlepas plesteran pada dinding pemikul beban pada kasus khusus)
  • Kategori C: Kemungkinan rusak komponen struktur dinding pemikul beban
  • Kategori D: Rusak dinding pemikul beban

Berikut informasi tingkat getaran mekanik berdasarkan dampak kerusakan dalam bentuk grafik:

Baku tingkat getaran mekanik juga dapat dibagi berdasarkan jenis bangunan. Jenis bangunan dibagi menjadi tiga yaitu:

  1. Bangunan untuk keperluan niaga, bangunan industri dan bangunan sejenis
  2. Perumahan dan bangunan dengan rancangan dan kegunaan sejenis
  3. Struktur yang karena sifatnya peka terhadap getaran tidak seperti tersebut pada no 1 dan 2, nilai budaya tinggi seperti bangunan yang dilestarikan

Berikut adalah nilai baku tingkat getarannya:

Untuk frekuensi > 100, sekurang-kurangnya nilai yang tersebut dalam kolom harus dipakai.

Tabel berikut di bawah adalah baku tingkat getaran kejut.

KelasJenis BangunanKecepatan Getaran Maksimum (mm/det)
1Peruntukan dan bangunan kuno yang mempunyai nilai sejarah tinggi2
2Bangunan dengan kerusakan yang sudah ada, tampak keretakan-keretakan pada tembok5
3Bangunan untuk dalam kondisi teknis yang baik, ada kerusakan-kerusakan kecil seperti plesteran yang retak10
4Bangunan kuat (misalnya bangunan industry terbuat dari beton atau baja)10 – 40

Pada peraturan tersebut, diatur juga metoda pengukuran dan analisis tingkat getaran sebagai berikut:

  1. Peralatan yang digunakan adalah:
    1. Alat penangkap (transduser) getaran (Accelerometer atau seismometer)
    2. Alat ukur atau alat analisis getaran (Vibration meter atau vibration analyzer)
    3. Tapis pita 1/3 oktaf atau pita sempit (Filter 1/3 oktaf atau narrow band)
    4. Pancatat tingkat getaran (Level atau X – Y recorder)
    5. Alat analisis pengukur tingkat getaran (FFT Analyzer)
  2. Prosedur pengukuran
    1. Getaran untuk Kenyamanan dan Kesehatan:
      • Alat penangkap getaran diletakkan pada lantai atau permukaan yang bergetar, dan disambungkan ke alat ukur getaran yang dilengkapi dengan filter
      • Alat ukur dipasang pada besaran simpangan. Dalam hal alat tidak dilengkapi dengan fasilitas itu, dapat digunakan konversi besaran.
      • Pembacaan dan pencatatan dilakukan untuk setiap frekwensi 4-63 Hz atau dengan sapuan oleh alat pencatat getaran.
      • Hasil pengukuran sebanyak 13 data digambarkan pada Grafik
    2. Getaran untuk keutuhan bangunan
      • Cara pengukuran sama dengan pengukuran getaran untuk kenyamanan dan Kesehatan manusia, hanya besaran yang dipakai ialah kecepatan getaran puncak (peak velocity)
    3. Cara Evaluasi
      • Ke-13 data yang digambarkan pada grafik dibandingkan terhadap batas-batas baku tingkat getaran. Getaran disebut melampaui baku tingkat getaran apabila getaran pada salah satu frekuensi sudah melampaui nilai baku getaran yang ditetapkan. Baku tingkat Getaran dibagi dalam 4 kelas yaitu a, b, c, dan d.

Definition

Definisi yang digunakan di peraturan Menteri lingkungan Hidup no 49 tahun 1996 adalah sebagai berikut

  1. Struktur bangunan adalah bagian dari bangunan yang direncanakan, diperhitungkan dan dimaksudkan untuk:
    • Mendukung segala macam beban (beban mati, beban hidup dan beban sementara)
    • Menjamin stabilitas bangunan secara keseluruhan dengan memperhatikan persyaratan kuat, kaku, dan andal. Misal: struktur kerangka kaku (frame), struktur dinding pemikul (Bearing wall)
  2. Komponen struktur adalah bagian dari suatu struktur bangunan, yang menjamin fungsi struktur. Misal: balok, kolom dan slab dari frame.
  3. Dinding pemikul adalah struktur bangunan berupa bidang tegak yang berfungsi mendukung beban diatasnya seperti slab lantai tingkat atau atap.
  4. Non struktur adalah bagian dari bangunan yang tidak direncanakan atau difungsikan untuk mendukung beban. Misal: dinding partisi, kerangka jendela/pintu.

Pengaruh kerusakan struktur dan non-struktur:

  1. Kerusakan pada struktur, dapat membahayakan stabilitas bangunan, atau roboh. (misalnya patok kolom bisa merobohkan bangunan).
  2. Kerusakan pada non struktur, tidak membahayakan stabilitas bangunan, tetapi bisa membahayakan penghuni (misal: robohnya dinding partisi, tidak merobohkan bangunan, tetapi bisa mencederai penghuni).

Derajat kerusakan struktur:

  1. Rusak ringan adalah rusak yang tidak membahayakan stabilitas bangunan dan dapat diperbaiki tanpa mengurangi kekuatannya.
  2. Rusak sedang adalah rusak yang dapat mengurangi kekuatan struktur. Untuk mengembalikan kepada kondisi semula, harus disertai dengan tambahan perkuatan.
  3. Rusak berat adalah rusak yang membahayakan bangunan dan dapat merobohkan bangunan. 

Ditulis oleh:

Hizkia Natanael
Acoustic Engineer
Phone: +6221 5010 5025
Email: hizkia@geonoise.asia

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