Sound Wave Phenomena

Sound waves are disturbances propagated in an elastic medium, gaseous, liquid, or solid. Seseorang receive sound vibration of the eardrum in a frequency region of human hearing. The vibrations generated from a variety of air pressure generated by the noise source and propagated into the surrounding medium, which is known as the acoustic field. When the sound hits a boundary of the medium through which it passes, then the energy in the sound waves can be transmitted, absorbed or reflected by the boundary. At third generally occurs in different degrees, depending on the type of boundary path. The phenomenon of sound waves that occur in the form of sound which is absorbed, reflected and transmitted can be seen in Figure.

Sound absorption

Sound Absorb represents a change in the energy of sound energy into heat energy or heat. Part of acoustic energy into the material is absorbed by the mass. Mass convert acoustic energy into heat energy, or rather a sound absorp. The ability of a material to absorb sound is usually measured by the coefficient of sound absorption. Factors that influence sound absorption is the material density, modulus of elasticity, moisture content, temperature, intensity and frequency of the sound, and the conditions on the surface of the material. Material density and modulus of elasticity that is low, and the water content and the high temperatures to absorb more sound. The quality of the sound damping material indicated by the price α (sound absorption coefficient of the material), the bigger the better α is used as a buffer suara.Nilai α range from 0 to 1. If α is 0, meaning no sound is absorbed while if α is 1, meaning that 100% sound that comes absorbed by the material. The amount of sound energy reflected, absorbed, or transmitted depent on the type and nature of the material or the material. In general, the porous material (porous material) will absorb sound energy that is greater than with other types of materials. The presence of pores causing sound waves can get into the material. Sound energy that is absorbed by the material to be converted into other forms of energy, is generally converted into heat energy. 
Absorber materials, reflective materials and diffuser material is a third class of acoustic material. One question that is often asked is how the response of these materials at a time when subjected to sound waves ?. How to make a soundproof room ?. How to talk in a classroom can be heard clearly ?.
To answer these questions need to understand the behavior of a material when subjected to sound waves. For details, see the following picture

 

From the illustration shown that when a sound wave on a material so some of the sound waves are reflected, some will be absorbed by the material and some will be forwarded.An acoustic material will be classified based on the ability of the dominant material for reflecting sound waves, sound-absorbing and sound waves continue. Sound-absorbing material is a material whose greatest ability is to absorb sound waves. Soundproof material is a material whose greatest ability is blocking the sound waves diterukan. While the voice spreader material is a material that has the function to spread the sound waves that come to him. This material requires a modification of a specific arrangement to achieve the desired spread of sound waves.Ability to absorb the sound waves of sound absorbent material (sound absorbing material) is expressed by the sound absorption coefficient (Sound Absorption Coefficient) whose value ranges from 0 to 1. A value of 0 indicates that the material really does not absorb sound energy that is coming, while a value of 1 indicates that all the noise coming energy absorbed by the material. however, these values ​​were never found on an acoustic absorbent material.The ability of a material to block out the sound energy into the room or otherwise with the transmission loss (TL, Transmission Loss). The ability of soundproof material can also be expressed STC (Sound Transmission Class). Selection of soundproofing materials are generally based on the value of this STC. The greater the value of STC material, the better the material is blocking the energy out or coming into the room.A material's ability to absorb or block the sound waves is dependent upon the frequencies of incoming waves. Absorbent material and soundproofing worked well certain frequencies.Thank you, may be useful.