Sound proofing and acoustic materials are used to attenuate, deaden, or control sound and noise levels from machinery and other sources for environmental amelioration and regulatory compliance. Sound proofing and acoustic materials can use either noise reduction or noise absorption. Noise reduction reduces the energy of sound waves as they pass through. Noise absorption suppresses echoes, reverberation, resonance and reflection.  Important specifications for noise reduction and noise absorption products include noise attenuation and noise reduction coefficient. Noise attenuation is the reduction in sound pressure level (SPL) that an acoustic product provides. It is measured in decibels (dB). Noise reduction coefficient (NRC) is the average of an acoustic material’s absorption coefficients at a specified set of frequencies, typically 256 Hz, 512Hz, 1024 Hz and 2048 Hz. Absorption coefficients range between 0 and 1 and are often evaluated at many frequencies in the audible range in order to create a performance curve for the material throughout the audio spectrum. 

Types of Soundproofing and Acoustic Materials

Many different types of sound proofing and acoustic materials are available. A vinyl acoustic barrier blocks airborne noise (street traffic, voices, music) from passing through a wall, ceiling, or floor. Because vinyl acoustic barriers are made of heavy, limp vinyl, they are usually built into the structure and then covered with a finished surface like sheet rock or paneling. Sound proofing foam dampens noise by making sound waves pass through multiple foam cells and foam cell walls. A sound proof room contains soundproofing material in the walls, floors, and ceilings. Acoustic foam and acoustic ceiling tile absorb sound to minimize echo and reverberation within a room. They do not block noise from transmitting through walls and ceilings. Sound proof doors and sound proof windows are also designed to reduce the transmission of sound.  Building techniques such as double wall construction and staggering wall studs can improve the soundproofing of a room. A sound proof wall can incorporate sound proofing and acoustic materials to meet desired sound transmission class (STC) values. For example, a wall with an STC rating of 25 would allow normal speech to be easily understood. With an STC rating of 50, shouting would be barely audible. A wall made with double 5/8-inch drywall on steel studs has an STC rating of 50. To measure the sound absorption of sound proofing and acoustic materials, it is important to determine the frequency range of interest, for example from 100 Hz to 5000 Hz.

Standards

Sound proofing and acoustic materials are covered by the International Organization for Standardization (ISO) Technical Committee 43 (acoustics) and by ASTM International, formerly called the American Society for Testing and Materials, ASTM Committee E33 (environmental acoustics), including ASTM E90. For fire safety considerations, sound proofing and acoustic materials can be covered by ASTM D3574 and D3675.

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