Masonry Magazine August 1967 Page. 29
NCMA TEK 9
©1967, National Concrete Masonry Association
An information series from National Concrete Masonry Association
Estimating Sound Transmission Class of Concrete Masonry
With each advance in our urban industrial civilization, the individual is subjected to an increasingly painful assault upon his auditory system. Yet with his improved standard of living, he finds annoying noise levels now intolerable and expresses his displeasure vocally and, if possible, financially. This tendency has become obvious, particularly in multi-family housing. Those who would rather move, do. Those who cannot, complain.
Noise was once limited by zoning the surrounding area for quiet; however, the trend in today's regulations is to specify the sound transmission class of walls and the impact noise resistance of floors. Architects and builders unfamiliar with these terms are required to estimate the sound insulation value of a wall prior to its construction by evaluating test data supplied by the manufacturer of the building material or data from other sources.
The problem of measuring sound transmission and reporting intelligent data which would permit the building designer to predict a wall's value as a sound insulator is complicated. This is due to the limited and changing "state of knowledge" as to how sound transmission should be measured and how it should be reported.
Measurements of sound transmission are obtained by employing a representative test panel which forms a dividing wall between two rooms, one containing a sound source, the other containing sound receiving equipment. Briefly, the test procedure involves generating a steady sound in the source room and measuring the sound level in both rooms. Differences in sound levels of the two rooms determines the transmission loss characteristics of the separating sample panel. The test is carried out at 16 different sound frequencies between 125 and 4000 cycles per second and the results can be plotted as a curve of TL versus Frequency such as illustrated in Fig. 1. Details of the above test procedure are listed in ASTM E 90-66T, "Laboratory Measurement of Airborne Sound Transmission Loss of