Acoustic property of building is based on acoustic nature of building materials and how sound is transmitted through the adjacent structural elements.
Noise is unwanted sound, that is considered as a nuisance in buildings for residential or domestic purposes. The buildings must possess good sound insulation property to have good acoustic feature.
Sound insulation of buildings is a property that must be considered in the initial stages of planning. Planning for the structural elements, to make them sound proof is one of the consideration. And the other one is the planning of the area, where the building should be located.
A building planned near to a roadway, which is highly traffic prone, would result in high inconvenience to the occupants residing there. More detailed view on the subject and its considerations are explained below.
Sound Insulation in Buildings
The sound insulation property of building materials is the ability in the reduction of sound across a partition. For a good conventional office building construction, the sound insulation is experienced good when it is in the range of 45dB.
This value can be explained as follows. If the room creates a sound of 65dB, then the receiver sitting in the adjacent room receives the sound at 20dB. This value is barely audible. Now if the level increase to 75dB, which is a raised voice, then the sound levels at the adjacent room will be 30 dB, which is clearly audible.
We must keep in mind that sound insulation gives the property of how much sound is lost and not the sound regained within the room. The unwanted and unexpected sound is always considered to be a noise and that really is a question of the acoustic property of the building.
Techniques to Reduce Unwanted Sound in Buildings
Certain physical techniques that are employed by engineers, architects, and builders to reduce noise impacts are explained under this section. Due to the scarcity of land as well as increasing population, the engineers are forced to undertake the available land and treat it as per our need.
So, major four actions which can be employed to reduce noise impacts, that are compatible with any type of land, activity or use are:
- Site Planning
- Methods in Construction
- Barriers in Construction
Building Site planning
The site planning method in acoustic property of buildings is to arrange the buildings on a zone of land, that would minimize severe noise impacts. This is done by capitalizing the natural shape as well as contours of the site.
One such step is to shield the residential area or other non-sensitive activities from noises by non-residential land, or an open space or by barrier buildings.
The architecture design method implements the noise reduction concepts in the details of the individual building elements. This stage is more concerned about the height, the room arrangement, the placement of balconies and the window.
Method of Construction
The individual elements of buildings can be improved by the variation of structural element materials or internal design to facilitate good sound insulation. This would reduce the noise transmission through wall, windows, doors, ceiling and floors. New soundproofing concepts have been developed which are related to this stage.
Barriers for Construction
Barriers for resisting noise, which is placed in between the noise sensitive areas and the source of noise. Different types of barriers are possible, like walls, fences made of different materials, planting trees and shrubs in thick, making berms out of earth and combination of individual elements.
Acoustic Properties of Building Materials
In many cases help from an acoustic designer is required after the building construction is complete and is occupied to high level of sound. The discomfort faced by the occupant residing or using it, have to go for redesigning the building for noise insulation.
So, it is always necessary to have a pre-planning, mainly for the building constructions that are prone to noise disturbances.
Now being aware of the acoustic properties of building materials to some extent would help us to have a right choice on the what material to be selected when acoustics is a concerned factor. Some of them are explained below:
Acoustic Properties of Masonry, Concrete or Stone Materials
Mass and rigidity property are the two factors that make a material to be highly noise resistant. The concrete wall is highly efficient than masonry. Masonry material made floor or wall do perform appreciably.
Massive materials like stone, concrete can stop high sound waves that are less resistant to less massive materials. Concrete slabs do perform good in the sound insulation activity.
Acoustic Properties of Wood and Related Products
These are less dense than masonry. They have a smaller performance in sound isolation. MDF woods are more massive that are added to certain interior walls to increase the massiveness. The most common material plywood, which is used in multilayer in interiors, to make it sound proof.
Mainly wood is used in rooms where perfect sounding is required. It can reflect sound which can be considered as an important property for sound treatment. It resonates easily which promotes absorption of sound, some of which pass through the material and some reflects. Therefore, these are used in making of instruments.
Acoustic Properties of Steel
Based on performance and structure, steel is one of the best material for sound insulation. Because of high cost, it has less application. It is highly dense and massive in nature.
Steel carries the sound through vibration within the material. This sound transfer is called as the structure-borne vibration. The normal case is airborne vibration which is not appreciable.
Acoustic Properties of Glass & Transparent Materials
The glass is massive in nature. There is a new development of absorptive glass-like materials that have the property to absorb more sound waves instead of reflecting. The material is made from Plexiglas or transparent foil thinner in nature with tiny holes. Their application comes in sound studios.
Acoustic Insulating Materials
Foam, fiberglass, rock wool etc. can be considered as the insulating materials we are familiar. The fiberglass material gains higher sound absorption property.
These materials absorb sound by reducing the velocity of particles that carry the sound waves in the air. Under low velocity, the pressure is high. Now wood materials absorb more sound at high pressure.
Sound waves gain higher pressure at room boundaries. So, care must be taken in the arrangement of boundaries or walls. For multiple boundaries like dihedral or trihedral walls, the sound waves are at higher pressures.
Acoustic Properties of Rubber and Plastic
The known materials are vinyl, neoprene etc. These materials are used to make low cost economical acoustical devices. But their use is almost considered limited. They can be used as mechanical isolators for floating glass, by preventing vibrations of the diaphragm to be transmitted to the walls.