Masonry Magazine April 1970 Page. 15

Masonry Magazine April 1970 Page. 15

Masonry Magazine April 1970 Page. 15
An Information series from National Concrete Masonry Association
NCMA TEK 18
© 1970 National Concrete Masonry Associates


Noise Control with Concrete Masonry in Multi - Family Housing


INTRODUCTION
The appliances available to the ordinary household increase with each passing year. Television sets, air conditioners, and a host of other devices are commonplace. The noise from these appliances inside the home is complemented by that from automobiles, high speed trains, and jet aircraft which permeate the outside environment. The noise problem found in multifamily housing is considerably greater than that in single family residences. Here the occupants of a given unit are not only exposed to noise from the exterior walls and noise generated in their own living area, but they are also exposed to noise from occupants of adjoining units. Statistical samplings have indicated that this type of noise is especially aggravating to people because of the intelligence it conveys. This includes such things as the intelligibility of voices, the slam of a closing door or the gush of running water. People want to be able to converse comfortably in the room they occupy, but they don't want to hear people talking in adjacent rooms. Above all, they don't want people in adjacent rooms to hear what they are saying. Studies and surveys of occupant desires show conclusively that people want residences which are sound-proofed between walls, rooms, and living units. At the same time, they want the continued use of modern appliances and transportation. Since it is not feasible to remove the cause of unwanted sound, designers of multifamily housing must control the acoustical environment. Concrete masonry is the economical building material which enables the designing architect or engineer to effectively respond to this challenge. In addition to being strong, fireproof, and attractive, concrete masonry is the building material of choice because it possesses excellent properties of sound absorption and sound insulation.

Sound may be pleasant and necessary, but when it becomes unwanted and annoying it is called noise. It is the attitude of the listener which makes the determination. There are two major sources of noise-airborne sound and impact sound.

Airborne sounds are produced by sources which radiate energy directly into the air, such as a dog barking or a radio playing. Impact noise originates from direct mechanical action such as a foot step, or a dropped object. Airborne sounds originated in a room may set up reverberations in the room itself, especially if the walls are made of hard, reflecting surfaces.

Three techniques are commonly used to reduce unwanted sound. The first is the elimination of the cause of the noise. Although this may be the ideal solution in the case of a vibrating machine or similar problem, elimination of the sources of sound in multifamily housing would be impractical if not impossible. The second method of reducing noise is to diminish the sound level within a room by employing materials which absorb the sound instead of reflecting it back into the room. The third means of limiting noise is to prevent sound waves from being transmitted from an adjoining area through the use of sound insulating material.


SOUND ABSORPTION
Sound absorption control involves reduction of sound emanating from a source within a room. The extent of control depends on the efficiency of the room surfaces in absorbing rather than reflecting sound waves. Sound is absorbed through dissipation of the energy of the sound wave in the form of heat.

The sound absorption coefficient is an indication of the sound absorbing efficiency of a surface. A surface which could theoretically absorb 100% of impinging sound would have a sound absorption coefficient of 1. Similarly, a surface absorbing 45% of incident sound would have a coefficient of 0.45 (Most materials are tested for sound absorption at frequencies from 125 to 4,000 cps in octave steps.) Another designator, termed the noise reduction coefficient (NRC) is calculated by taking a mathematical average of the sound absorption coefficients obtained at frequencies of 250, 500, 1,000, and 2,000 cps. Table 1 lists the approximate NRC values of both light and heavy concrete masonry. The listed NRC values depend on the porosity of the material and the surface texture.

Table 1 Approximate Noise Reduction Coefficients

| Material | Surface Texture | Approximate NRC |
| ----------- | ----------- | ----------- |
| Lightweight Aggregate Block, Unpainted | Coarse | 0.40 |
| | Medium | 0.45 |
| | Fine | 0.50 |
| Heavy Aggregate Block, Unpainted | Coarse | 0.26 |
| | Medium | 0.27 |
| | Fine | 0.28 |

Deduct from above for painting

| Paint | Application | One Coat | Two Coats |
| ----------- | ----------- | ----------- | ----------- |
| All | Spray | 10% | 20% |
| Oil | Brush | 20% | 55% |
| Latex | Brush | 30% | 55% |
| Cement | Brush | 60% | 90% |


Masonry Magazine December 2012 Page. 45
December 2012

WORLD OF CONCRETE

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Masonry Magazine December 2012 Page. 46
December 2012

Index to Advertisers

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Masonry Magazine December 2012 Page. 47
December 2012

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Masonry Magazine December 2012 Page. 48
December 2012

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