Technical Information | Noise Control

(Excerpted from Noise Control with Concrete Masonry, published by CMACN)

Desert Block Co., Inc. supplies this information as an educational aid in understanding the benefits of concrete masonry construction and our products. It is the responsibility of the user to obtain engineering or other advisory services from licensed professionals as the basis for incorporating into any project any information, detail, or product offered herein.

Why Masonry?

Masonry structures are particularly well suited to the requirements of noise control in multi-family structures. Concrete block masonry wall assemblies provide a density of material with the noise reduction values needed to minimize tenant annoyance and comply with recognized standards. Sound transmission ratings are achieved with masonry construction for the reduction of the noise from freeways, rail movements, and aircraft operations or nearby industrial activity. Sound rated masonry wall systems tested by application of standardized laboratory procedures are available to the architect for combating these exterior noise sources, as well as the undesirable sounds which may be experienced between dwelling units in multi-family construction.

To exemplify the advantage of masonry construction, Figure 2 shows the variation of sound rating to wall weight. It is noted that increasing the weight of the wall generally improves the STC value in accordance with the accepted "Mass Law" sound transmission characteristics.

This guide specifically addresses the question of masonry wall design as needed to provide the isolation from exterior noise and the insulation of sound between living units to meet the requirements of the State Standards.

Figure 2. STC vs. wall weight for single wythe painted or plastered block walls

Isolation vs. Insulation

The distinction between isolation and insulation as they relate to the Standards must be emphasized. This important distinction is described as follows:

Isolation of interior spaces from exterior sources is measured by positioning one sound level meter in the room of concern and another directly outside. The difference in the 'A-weighted sound level' measured by each instrument is a direct measure of the isolation provided by the building. The difference depends on that portion of the sound energy which entered the room and was not absorbed by the interior furnishings, carpeting, drapes and walls, as well as the sound transmission loss through the exterior walls, roof, windows, doors and vents. It should be emphasized, when considering the isolation portion of the Standards, the sound absorption provided by the interior space is an important part of the reduction between interior and exterior noise levels.

The Standards specify a minimum amount of insulation for party wall and floor/ceiling separations between the dwelling units by application of the Sound Transmission Class (STC). This one-numbered rating of the sound transmission characteristics of building assemblies is accepted by the architects, building officials, building tradesmen and the various suppliers of components which make up a wall or floor/ceiling separation. The scheme assigns a one number rating to the 16 values of Sound

Transmission Loss (TL), data obtained by application of the appropriate American Society for Testing and Materials (ASTM) standards.

It is important to recognize that these transmission loss values for wall or floor/ceiling assemblies are independent of the sound absorption in either the source or receiver room. It is the noise insulation characteristics of the separation between dwelling units that has been specified in the Standards, and not the noise reduction between units.

Figure 3. Insulation by Sound Transmission Control

STC Values of Masonry Walls

Masonry wall systems which meet or exceed the design requirement of an STC of at least 50 are listed in Table A. In addition to the rated wall assemblies which are suitable for compliance with the State Standard, wall assemblies with lower ratings which may be used to control the noise from exterior sources have been included in Table A.

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