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Acoustic Design According to Room Shape

The shape of the room defines the movement of the sound waves within the room. Placement of acoustic materials should be determined by the way the sound moves in that particular room in order to ensure optimal efficiency of the materials.


Placing the sound absorbing materials on the ceiling in a narrow room will not create the wanted acoustic effect. 

Sound absorbers must be placed as close to the sound source as possible. Therefore, the absorbing materials must primarily be placed on the walls


The sound moves towards the constructive centre thereby creating echoes.

The sound diffusing elements should be placed on the curved surfaces in order for the sound to be dispersed in many directions.


In large rooms the sound spreading is experienced as the greatest challenge, since the speech sounds can be heard over long distances.

Sound absorbing and sound diffusing materials should be used, and sound barriers should be applied to the ceiling. The sound regulation from the floor is secured by furniture and the use of sound barriers.


The acoustic environment in large rooms is sometimes experienced as the one at a railway station. This is partially connected to the fact that it is difficult to concentrate due to the relatively high noise level. Another reason for this is the fact that the conversation over short distances is impeded due to the sound being masked or drowned by the surrounding noise 

It is therefore important that all the available surfaces are equipped with effective sound absorbers and sound diffusers. The furniture along with the sound barriers play a highly active role by diffusing the sound and thereby making the existing sound absorbers and diffusers even more efficient.


In small rooms, the low frequencies often seem to be predominant. Therefore, the speech appears to consist primarily of humming sounds. Sound absorbers with a low-frequency profile should be used and placed on the ceiling surface.


The sound diffusing elements should be placed on the curved surfaces in order for the sound to be dispersed in many directions.


Inclined ceilings have both a sound spreading and a sound concentrating effect. In most cases, the sound is concentrated because the sound regulation of the area around the inclined ceiling has not been considered carefully.

The wall area opposite the inclined ceiling should also be equipped with sound absorbing materials. As a principal rule, all surfaces above the normal ceiling height (2.60 m) including the end walls should be equipped with sound absorbers.


Inclined walls have both a sound spreading and sound concentrating effect. 

The sound spreading effect is achieved by inclining the wall in proportion to other walls and the ceiling. In general, the walls inclined by more than 6 degrees ensure an excellent sound diffusion. The most effective diffusion is obtained by applying several angles.


In rooms with vaulted ceilings, the sound is concentrated in the constructive centre making the sound appear with a stronger intensity. The sound movements also appear stronger along the curve.


Rooms that are linked by a large opening in between, influence each others sound environment. A room without acoustic regulation can act as an echo chamber reinforcing the sound, when connected to an acoustically regulated room.

Both rooms must be equipped with sound absorbers. If the distance between the opening and the opposite walls is short (5-6 m), the walls much be covered with sound absorbers or diffusers.


In rooms with mezzanine, it is possible to create different sound environments in the same room. In the large, open room, an environment with long reverberation time is created. The space above and below the mezzanine has a shorter reverberation time. The challenge posed in this type of rooms is the sound reflection and the harmonization of the different reverberation times.

The wall opposite the mezzanine should be equipped with sound absorbers or diffusers. In addition, sound absorbers should be placed on the underside and the banister of the mezzanine. In order to prevent large differences in the reverberation times between the large room and the space around the mezzanine, sound barriers can be applied.


Check out our free reverberation online calculator (for basic rooms).

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 


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.