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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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The power of trees can reduce noise.

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

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

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

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

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

Do Plants Help to Absorb Sound?

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

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

How Plants Reduce Indoor Noise Levels?

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

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

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

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

Reference :

พลังจากต้นไม้ ลดมลพิษทางเสียง

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

The Top Sound Absorbing Plants For The Workplace

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SCOPE OF ARCHITECTURAL ACOUSTIC CONSULTANT’S WORK

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

by Ramadhan Akmal Putra 

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Accelerometer mounting

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

 

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

 

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

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

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

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

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

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

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

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

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

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

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Industrial Noise Control Measure

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

Noise sources

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

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

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

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

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

Steps to control noise in workplace

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

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

To reduce exposure to noise

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

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

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

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

Engineering solutions to reduce noise

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

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

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

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

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

General measures to keep in mind

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

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

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

Conclusion

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

Reference

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

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

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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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Asia Noise News Building Accoustics Building Acoustics Environment Home Industrial Noise and Vibration Product News Noise-th Uncategorized Vibration Virtual Data Room

Helmholtz Resonator

Helmholtz resonator
Helmholtz resonator

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

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

Helmholtz resonator

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

 

Calculate Resonant frequency of Helmholtz Slot Absorber

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

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

Credit : mh-Audio.nl , acousticfields

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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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Environment Industrial Noise and Vibration Product News

Noise Monitoring for your home, Thailand

 

The first DIY noise monitoring, easy to use and install, just plug in the power, wifi and ready to go, online data noise monitoring, accurate, calibrated, weatherproof. Automated alarms by email or messenger.

Noisy neighbours, noise from entertainment or from a factory, road noise?

Register the noise and discuss with the authorities how to resolve the issue.

SpotNoise noise monitoring from the Netherlands, now available via Geonoise Thailand for South East Asia.


Noise Nuisance Monitoring Thailand Noise Nuisance Monitoring Thailand, Malaysia, Indonesia, Vietnam

 
 
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