Transmission Loss of Selected Absorptive Assemblies

The transmission loss table shown here reflects the Sound Transmission Class (STC) levels of some of ATCO Noise Management's acoustic assemblies for frequencies from 31.5 Hz to 8000 Hz. The performance values for frequencies from 125 Hz to 8000 Hz were determined from independent laboratory testing to ASTM E90-90 which is equivalent to ISO 140-1/2/3-1978 and DIS 140-1/3-1994.

Frequencies below 125 Hz can not be tested in acoustical laboratories; however, ATCO Noise Management has performed extensive field testing on its assemblies in the lower frequency ranges.

SOUND TRANSMISSION LOSS (TL) - Transmission Loss is the logarithmic ratio of the sound power on one side of a barrier (wall or partition) to the sound power transmitted to the other side.

OCTAVE BAND - Frequency ranges in which the upper limit of each band is twice the lower limit is known as an octave band. In industrial noise studies, nine octave bands are most commonly used.

FREQUENCY - Pressure variations travel through the air in the form of sound waves. The number of sound waves produced by a noise source passing a given point per second is known as its frequency.

HERTZ (Hz) - Units of frequency are measured in Hz. A Hz is numerically equal to cycles per second.

SOUND TRANSMISSION CLASS (STC) - For convenient comparison of different constructions, it is necessary to have a single rating that puts the performance at all frequencies into perspective. The sound transmission class (STC), introduced by the American Society for Testing Materials (ASTM) is most commonly used for this purpose. The STC rating is derived from the transmission loss (TL) value of a wall measured at different octave band frequencies.

NOISE REDUCTION COEFFICIENT (NRC) - A measure of the acoustical absorption performance of a material, calculated by averaging its sound absorption coefficients at 250, 500, 1000 and 2000 Hz expressed to the nearest multiple of 0.05.

Last updated: 05-May-2002