Building Design and Construction Handbook - Merritt - Ventech!

WALL, FLOOR, AND CEILING SYSTEMS 11.151
or even narrower ranges). Usually, the sound-level meter contains filters and circuitry
to bias the readings so that the instrument responds more like the human
ear—‘‘deaf’’ to low frequencies and most sensitive to the midfrequencies (from
about 500 to 5000 Hz). Such readings are called A-scale readings. Most noise level
readings (and, unless otherwise specifically stated, most sound pressure levels with
no stated qualifications) are A-scale readings (often expressed as dBA). This means
that actual sound pressure readings have been modified electrically within the instrument
to give a readout corresponding somewhat to the ear’s response (Fig.
11.91).
For various measurements and evaluations of performance for materials, constructions,
systems, and spaces, see Art. 11.81.
11.79 SOUND AND VIBRATION CONTROL
This process consists of:
1. Acoustical analysis
a. Determining the use of the structure—the subjective needs
b. Establishing the desirable acoustical environment in each usable area
c. Determining noise and vibration sources inside and outside the structure
d. Studying the location and orientation of the structure and its interior spaces
with regard to noise and noise sources
2. Acoustical design
a. Designing shapes, areas, volumes, and surfaces to accomplish what the analysis
indicates
b. Choosing materials, systems, and constructions to achieve the desired result
Sound and vibration sources are usually speech and sounds of normal human
activity—music, mechanical equipment sound and vibration, traffic, and the like.
Characteristics of these sound sources are well known or easily determined. Therefore,
the builder or designer is usually most interested in the transmission paths for
sound and vibration. These are gases (usually air); denser fluids (water, steam, oil,
etc.); and solids (building materials themselves). During sound transmission in a
building, some of the sound energy is absorbed or dissipated, some is reflected
from various surfaces, and some is transmitted through the building materials and
furnishings.
Sound control is accomplished by means of barriers and enclosures, acoustically
absorbent materials, and other materials and systems properly shaped and assembled.
Vibration control is accomplished by means of various resilient materials and
assemblies, and by damping materials (viscoelastic materials of various types).
Airborne and structure-borne energy are controlled by somewhat different techniques,
described in the following.
11.79.1 Airborne Sound Transmission
A sound source in a room sets the air into vibration. The vibrating air causes any
barrier it touches (partitions, floors, ceilings, etc.) to vibrate. The vibrating barrier,