Sound is the sensation caused in the ear by the vibration of the surrounding air or other medium. Musical sound is very pleasant to hear and it has been established that it has a smoothing effect on listeners. But on the other hand when the sound is not pleasing, it becomes unwanted and turns into noise. Acoustic and noise control plays a very important role in the design and construction of buildings.
Image: Flickr, Lotus Temple, Tracy Hunter – "This place was designed by an Iranian architect named Fariburz Sahba. I thought the inside had terrible accoustics as sounds were echoed off the walls."
Increased traffic on the roads and railways, the working of machineries in the factories, the zooming sound from aero planes, etc. all add to the noise level. When this noise level crosses permissible limits, it causes lots of problems for listeners.
The other day, it was reported in newspapers that a senior political leader who had come in connection with a public function almost became deaf due to the piercing sound generated by fire crackers.
Noise can be classified into two groups: air borne and impact noise. Air borne noise is transmitted through air as the medium while impact noise is generated from an impact on a structure.
Effects of Noise
The effects of noise are many; its intensity depends on the loudness of the sound. Noise causes fatigue, irritation, loss of efficiency, and permanent damage to hearing. Experiments have indicated that sound levels of 90 dB and above decrease the efficiency of workers and sound of 135 dB and above may even cause instantaneous rupture of the eardrum.
Annoyance to any person on account of noise will vary depending on the nature of the noise, its steadiness, and whether or not it has a fluctuating frequency.
Methods of Noise Reduction
The effects of noise can be reduced by adopting the following methods:
The building should be located away from the main source of the origination of sound. Hospitals, schools, auditoriums, residential colonies, etc. should be so located that they are far away from sound sources. The location of doors and windows is also important. They should be provided in such a way so that there is no direct entry of noise inside.
Machines which produce much noise should be provided with a bed of cork or rubber. Also insulation against noise can be obtained by providing impervious partitions.
The frictional noise coming out of rotating machines can be reduced by proper lubrication. Providing resilient materials like cork, glass wool, rubber, etc. between the source of sound and structure helps in reducing structural-borne noise and vibrations.
Image: Flickr, Acapella: The Accoustics, angkorianboy
Sound Construction and Engineering
The behavior of sound plays a very important role in the acoustics of buildings. When a sound originates from a source, it travels in all directions through different mediums and strikes objects such as a walls, floors, and ceilings. Part of the sound is absorbed while another part is reflected back. The reflected sound may cause echo, reverberation, and acoustical defects. This reflected sound has to be controlled so that no disturbance is created.
The following points should be taken into consideration in the design and construction of auditoriums, cinema halls, lecture theaters and broadcasting studios.
- The sound should be of adequate intensity so that it can be heard in each and every corner of the hall.
- In lecture halls, the sound should be clear and distinct so as to avoid distortion.
- In halls for music and dance programs, the sound should reach the audience with the same frequency and intensity.
- Disturbances from outside a hall should be reduced so that it does not interfere with the normal hearing of speech or music.
- A Text Book Of Building Construction and Construction Materials, G S Birdie, T D Ahuja, Dhanpat Rai Publishing Co, New Delhi,2007
- Construction Engineering and Management , S Seetaraman, Umesh Publications, New Delhi,2003
Link: Noise Control Engineering