Sound is a form of energy that travels through air on any other medium in the form of a vibration and can be heard by the human ear. The speed of sound depends primarily on the medium through which the sound waves pass. The human ear is extremely sensitive and can hear sounds of only low power intensities. The hearing range of a human lies in the area between 0 dB, known as hearing threshold and 120 dB, known as pain threshold. The frequency range of human hearing spans between 20 – 20000 Hz.
When sound energy hits against a surface like roof, floor or wall, some of it is absorbed by the material, part of it is reflected and the remaining sound is transmitted through as shown in the figure.
The amount of sound reflected, absorbed or transmitted depends on the shape of the material or the construction hit by the sound wave, and the frequency of the sound.
‘Room acoustics’ is a term which describes how sound waves interact with a room. If the room has nearly no sound absorbing surfaces (wall, roof and floor), the sound will bounce between the surfaces and the listener will not be able to listen clearly as both the direct as well as reflected sound waves(reverberation) are simultaneously heard. The sound itself will take a long time before it dies out. However, if the surfaces use sound absorbing material, the reflected sound will reduce to a considerable extent and the listener will only hear the direct sound. The room will also be much quieter.
While designing a building or even one’s own house, a special acoustic design is required. The following two sound-related factors should to be considered when designing a building:
The elevators, pumps, heating equipment, etc. should be noise free.
The sound in building should be reduced by room acoustics and sound insulation.
The passage of sound into one room from another room or outside the building is termed ''sound transmission". There are 2 metrics used to measure the performance of a wall in terms of its effectiveness in allowing the sound energy to pass through it. On one hand, Transmission loss is measured in units of Sound Reduction Index, R dB, which is a measure of the effectiveness of a wall, floor, door or other barrier in restricting the passage of sound. The higher the transmission loss of a wall, the better it functions as a barrier to the passage of unwanted noise.
On the other hand, Transmission loss is also measured in units of Sound Transmission Class, STC, which also is the measurement used to calculate how effective the sound transmitting materials are in reducing sound transmission between rooms. STC is measured by the decibel reduction in noise a material/partition can provide, abbreviated 'dB'. In simple words, it measures how much sound a wall will block from getting through to the other side.
In order to increase the STC or R dB levels of walls and ceilings, so that they provide maximum sound insulation, additional measures during wall construction are required. Some of the options available are:
Metal wall studs - It is helpful to use metal wall studs instead of wooden studs in a drywall which will help increase the transmission loss through the drywall.
A Double layered drywall - Another way to achieve better performance is to apply a second layer of 1/2-inch gypsum wallboard to one side of the wall. This gives the surface more mass, making it less prone to vibrate at the same frequency of sound waves, thereby increasing the resistance to passage of sound waves.
Sound isolation systems. An even more effective way to build an interior wall is not to mount 1/2-inch gypsum wallboard directly on wall studs but to special Z shaped channels or clips that run across the wall. These channels allow the gypsum board attached to it to vibrate when sound energy hits it causing the conversion of sound energy to vibrational energy, thereby reducing the resultant sound conducted through the wall studs, leading to an increase in STC/Rw dB rating of the drywall. Adding Rockwool/Glasswool insulation in the stud cavity, also increases the performance of a double layered drywall.
Comentarios