In this lecture, we are going to learn about the Factors Affecting Acoustics of Building and Their Remedies in a very detailed manner so let’s start one by one the factors that are affecting the acoustics, and then we will see the remedies of its effect.
The various factors affecting the acoustics of building such as reverberation time, loudness, focusing, echo, echelon effect, resonance, and noise with their remedies are explained briefly in this section.
Reverberation is the persistence of prolongation of sound in a hall even after the source stopped emitting sound.
- The reverberation time is the time taken by the sound to fall below the minimum audibility level.
- In order to have a good acoustic effect, the reverberation time has to be maintained at optimum value. The reason is, if the reverberation time is too small, the loudness becomes inadequate. On the other hand, if reverberation time is too long, it will lead to more confusion due to mixing or different syllables. This makes the sound unintelligible. Thus, reverberation time would neither be too large nor small.
- Hence, to maintain a good acoustic effect the reverberation time would be maintained at optimum level.
- The reverberation time can be eliminated at an optimum value by adopting the following ways:
- By providing windows and openings.
- By having full capacity of audience in the hall or room.
- By using heavy curtains with folds.
- By covering the floor with carpets.
- By decorating the walls with beautiful pictures, maps, etc.
- By covering the ceiling and walls with good sound-absorbing materials like felt, fiber board false roofing, etc.
- The reverberation time depends on o the size of the hall and the quality of sound. Thus, the reverberation time can be controlled wither by inserting or removing sound-absorbing material in a hall or room.
- The uniform distribution of loudness in a hall or a room is an important factor for satisfactory hearing. Sometimes, the loudness may get reduced due to excess sound-absorbing materials used inside a hall or room.
If the loudness of sound is not adequate, the loudness can be increased by adopting the following methods:
- By using suitable absorbents at places where noise is high. As a result, the distribution of loudness may become uniform.
- By constructing a low ceiling for the reflection of sound towards the listener.
- By using large sounding boards behind the speaker and facing the audience.
- By using public address systems like loudspeakers.
3Focusing and Interference Effect
- The presence of any concave surface or any other curved surface in the hall or room may make the sound to be concentrated at this focus region. As a result, the sound may not be heard at all in other regions. These regions are referred to as dead space. Hence, such surfaces must be avoided.
- In addition to focusing there should not be interference of direct and reflected waves. This is because constructive interference may produce a sound of maximum intensity in some places and destructive interference may produce a sound of minimum intensity in other places. Thus, there will be an uneven distribution of sound intensity.
- Curved surfaces can be avoided. If curved surfaces are present, they should be covered with suitable sound-absorbing materials.
- An echo is heard due to the reflection of sound from a distant sound-reflecting object.
- If the time interval between the direct sound and reflected sound is less than 1/15th of a second, the reflected sound is helpful in increasing the loudness. But, those sounds arriving later than this cause confusion.
- An echo can be avoided by covering long-distance walls and high ceilings with suitable sound-absorbing material. This prevents the reflection of sound.
- It refers to the generation of a new separate sound due to multiple echoes. A set of railings or any regular reflecting surface is said to produce the echelon effect. This echelon effect affects the quality of the original sound.
- The remedy to avoid the echelon effect is to cover such surfaces with sound-absorbing materials.
- Resonance occurs due to the matching of frequency. If the window panels and sections of wooden portions have not been tightly fitted, they may start vibrating, thereby creating an extra sound in addition to the sound produced in the hall or room.
- The resonance may be avoided by fixing the window panels properly. Any other vibrating object which may produce resonance can be placed over a suitable sound-absorbing material.
- The hall or room should be properly insulated from external and internal noises. In general there are three types of noises:
- Air-borne noise
- Inside noise.
- Extraneous noises which are coming from outside through open windows, doors, and ventilators are known as air-borne noise. The air-borne noise can be avoided by following the remedies mentioned below.
- The hall or room can be made air conditioned.
- By using doors and windows with separate frames with proper sound-insulating material between them.
- The noise which is conveyed through the structure of the building is called structure-borne noise. The structural vibration may occur due to street traffic, operation of heavy machines, etc.
- This noise can be eliminated by using double walls with air space between them.
- By using anti-vibration mounts this type of noise can be reduced.
- By covering the floor and walls with proper sound-absorbing material this noise can be eliminated.
- The noises which are produced inside the hall or room is called inside noise. The inside noise may be produced due to machinery like air conditioners, refrigerators, generate fans, typewriters, etc.
- To avoid these inside noises the following remedies can be adopted.
- The sound-producing machinery can be placed over sound-absorbing materials like carpet, pads, wood, felt, etc.
- By using curtains of sound-absorbing materials.
- By covering the floor, wall, and ceiling with sound-absorbing materials.
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