Masonry Technical Library - Masonry Acoustics and STC Ratings

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		A complete study of sound control within the built environment would be incomplete if it did not extend it's scope from walls to floors and ceilings. The chain is only as good as it's weakest link, therefore the acoustic characteristics of all aspects of a given design must be observed. With the use of Hollow Core slabs, the acoustic characteristics of floors and ceilings can be as good or better than the walls, insuring a sound design.


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TABLE OF CONTENTS

INTRODUCTION

The Science of sound

Determining STC Ratings

Designing for optimum performance

Sound Research Data - A list of STC Ratings for several common wall systems

Precast Hollow Core Floor Systems

Special Acoustic Units

Conclusion

Sound Transmission

Airborne sound reaches the floor, vibrates it, and is radiated through the floor material. Airborne sound transmission loss is most greatly affected by the weight of the material. The relationship of S.T.C. value and floor weight is clearly shown below in Figure 4. For this reason,a hollow core, precast concrete floor systems does not require any additional treatments in order to provide good sound insulation.

Impact noise reduction

Footsteps, slammed doors, and mechanical equipment can all cause their own brand of unwanted noise. Even when airborne sounds are controlled, there still can be severe impact noise problems. Impact sound insulation is tested per ASTM E492, Laboratory Measurement of impact sound transmission using a tapping machine. Impact transmission is not significantly affected by the weight of the floor. To control impact sounds, a structural concrete floor in combination with a carpet & pad greatly reduces the amount of impact noise (measured as IIC). Figure 5 below shows the sound control potential of the hollow core slab used in conjunction with a carpet and pad system.






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