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Asia Noise News Building Accoustics Environment Industrial

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.

1. NARROW ROOMS 

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

2.ROUND ROOMS 

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.

3.1 LARGE ROOMS WITH LOW CEILING

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.

3.2. LARGE ROOMS WITH HIGH CEILING

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.

4. SMALL ROOM WITH PARALLEL WALLS 

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.

5. CEILING DOMES

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

6. INCLINED CEILING

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.

7.INCLINED WALLS

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.

8. VAULTED CEILING

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.

9. CONNECTED ROOMS

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.

10. ROOMS WITH MEZZANINE

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.

Credit: KNAUF DANOLINE

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

https://www.geonoise.com/reverberation-time-calculator/

Categories
Asia Noise News Building Acoustics Environment Industrial Vibration

Building Vibration Limits in Indonesia

A lot of activities and businesses have the potential to have negative effects to their environment because of the vibration that they produce. For example, construction (for example during piling), mining and and other vibration-generating activities. This vibration can disturb the comfort and health of people around it, and even can have destructive effects to nearby buildings.

In Indonesia, the vibration limit is regulated through Ministerial Decree of Ministry of Environment No. 49 Year 1996. This regulation was made to ensure healthy environment for human and other living creatures to live in. Consequently, the vibration generated from human activities need to be regulated.

In this regulation, businesses and activities are required to:

  1. Comply to the vibration limit in the decree. This is required for businesses and activities to obtain certain relevant permits to be able to operate.
  2. Use vibration reduction equipment
  3. Report vibration monitoring activities at least once in 3 (three) months to the Governor, Minister, Government agencies that are responsible to control environmental impact, other technical institutions that is responsible for the activities and other organizations that might need the vibration monitoring report.

The vibration limit is separated into few parts which are:

  1. Vibration limits for health and comfort
  2. Mechanical vibration limits based on its destructive effects
  3. Mechanical vibration limits based on building types
  4. Shock limits

The following table and graphs is the vibration limit for health and comfort:

Conversion:

Acceleration = (2πf)2 x displacement

Velocity = 2πf x displacement

The graphic representation of the table above is as follows:

The table below is the vibration limits based on the destructive effects:

As seen above, the peak velocity limit from the vibration is separated into 4 categories which are:

  • Category A: non-destructive
  • Category B: Possibly destructive for plastering (crack, or in certain cases the plaster can fell off the wall) 
  • Category C: Possibly destructive for structural components that bear loads
  • Category D: High risk of destruction of load bearing walls

The following graph is the vibration limit based on destructive effects in a graphical form:

Mechanical vibration limit can also be categorized into the types of buildings. The buildings are categorized into 3 which are:

  1. Buildings for commercial, industrial, and other similar use.
  2. Residential and other buildings with similar design and usage
  3. Structures that are sensitive to vibration and cannot be categorized into category 1 and 2, for example preserved buildings with high cultural value

Below is the vibration limits for the building category above:

The table below is shock limit for buildings:

CategoryBuilding TypeMaximum velocity (mm/s)
1Old buildings with high historical value2
2Buildings with existing defects, cracks can be seen on the walls5
3Buildings with good condition, minor cracks on plaster is acceptable10
4Buildings with high structural strength (for example industrial building which is made from concrete and steel)10 – 40

The ministerial decree also describe the measurement and analysis method for vibration as follows:

  1. Instruments:
    1. Vibration transducer (Accelerometer or seismometer)
    2. Vibration measurement device or analysis device (Vibration meter or vibration analyzer)
    3. 1/3 octave or narrow band filter
    4. Signal recorder
    5. FFT Analyzer
  2. Measurement procedure:
    1. Vibration measurement related with health and comfort:
      • Place transducer on the floor or other vibrating surface, and connect it to the measuring device with filtration
      • Set the measuring instruments to measure displacement. If the measuring instruments do not have that on display, the conversion from acceleration or velocity can be used
      • Reading and recording is conducted for frequency between 4-63 Hz or with signal recording device
      • Measurement results with at least 13 data shall be plotted on graph
    2. Vibration measurement for structural health:
      • The measurement method is similar with the vibration measurement above, however the physical measure that is assessed is the peak velocity.
    3. Evaluation
      • The 13 data which are plotted on graph shall be compared with the vibration limits. The vibration is considered above the limit if the vibration level exceeds the limit at any frequency.

Definition

The definition used in the regulation of ministry of environment No 49 Year 1996 is as follows:

  1. Building structure is a part of building that is planned, calculated, and functioned to:
    • Support any kind of load (static load, dynamic load, and temporary load)
    • Functioned for building’s stability as a whole. For example: frame and bearing wall
  2. Structure’s component is a part of a building structure that contributes to structure’s function. For example: beams, columns, and slab.
  3. Bearing wall is a building structure which is a vertical plane that is functioned to support loads on top of it such as slab or roof.
  4. Non-structure components are parts of building that is not planned or functioned to support load. For example partition walls, door and window frames, etc.

Destructive impact on structure and non-structure:

  1. Destructive impact on structure: Destructive impacts that can endanger building stability (for example destruction of columns that potentially make a building collapses)
  2. Destructive impact on non-structure: Not dangerous to building stability, but can be a danger for building occupants (for example: when a partition wall collapses, it will not make the building collapse, but can injure occupants)

Degree of building destruction:

  1. Light: not dangerous for building stability and can be fixed without reducing building’s strength
  2. Moderate: Destruction that can reduce structural strength. To fix this, added reinforcement must be used.
  3. Severe: Degree of destruction that can endanger the building and potentially makes the building collapses.

Written by:

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

Categories
Asia Noise News

Acoustics Glossary

Get a better understanding of acoustics with our glossary of terms. Let Geonoise Asia help you solve your noise problems today!

Arranged by:

Adetia Alfadenata

Acoustic Engineer

Geonoise Indonesia

support.id@geonoise.asia