TM 5-805-4/AFJMAN 32-1090
CHAPTER 10
NOISE AND VIBRATION MEASUREMENTS
10-1.
Objective.
The Type 1 Sound Level Meter has the tightest
specification on frequency response, precision and
In the event that demonstration of compliance
stability. This meter is fitted with a microphone; it
with noise or vibration criteria is required, sound
has a stable amplifier, controllable attenuators,
or vibration measurements will be required.
and a meter that permits reading of sound levels
Within the scope of this manual, sound and vibra-
over a wide range of values, such as from 30
tion measurements and instrumentation might be
decibels to 130 decibels sound pressure level (SPL)
involved in two types of situations: noise and
or more. The accuracy of the reading may be
vibration in buildings, and community noise or
expected to be within 1 to 1.5 dB of the true SPL.
measurements. This chapter discusses these sub-
This instrument also has the A-, B-, and C-
jects.
weighted filters that are held to within specified
10-2. Sound And Vibration Instrumentation.
tolerances, and the meter has a "slow" and a
"fast" response. At the "slow" setting, the meter
Instrumentation for measuring sound and vibra-
in effect integrates the sound pressure level fluctu-
tion vary widely in complexity and capability.
ations of the last half second (approximately) and
However most sound and vibration level measure-
shows the "average" of that fluctuating signal.
ments for building mechanical equipment systems
The "slow" setting is used for readings of "contin-
can be obtained with hand-held, battery operated
uous" noise, i.e., noise that is produced by a
meters. A basic sound level meter consists of a
continuing sound source without any noticeable
microphone, electronic circuits, and a display. Vi-
periodic change (a fan would be considered a
bration measurements can be made with a sound
"continuous" source of noise, a pile drive would
level meter if the microphone is replaced with a
not). The "fast" response integrates the fluctua-
vibration transducer. The most common vibration
tions of the last 1/8 second (approximately); thus
transducer is an accelerometer. With the use of an
the needle jumps back and forth over a wider
accelerometer the meter will display acceleration
range of the meter face as it attempts to follow all
level in dB. Many sound level meters are equipped
short-term instantaneous changes. The Type 2
with "internal calibration" capabilities. While this
Sound Level Meter has slightly less stringent
is adequate for checking the internal electric
specifications than apply to the Type 1 meter. The
circuits and display, the internal calibration does
A-, B-, and C-weighted networks and the direction-
not check the operation of the microphone or
ality limits of the microphone are slightly relaxed.
accelerometer. Therefore it is highly recommended
The Type 3 Sound Level Meter is for general
that all sound level meter systems be equipped
survey applications, where still less accuracy is
with a separate calibrator. Sound level calibrators
acceptable. The Type 3 instrument is not accept-
able for OSHA use, nor for any noise level applica-
generate a known sound level and vibration cali-
brators generate a known vibration signal. As a
tion involving compliance with noise codes, ordi-
m i n i m u m the sound level meter should be
nances, or standards. The Type S Sound Level
Meter may be a simplified version of any of the
equipped with internal filters providing the capa-
Type 1, 2, or 3 instruments. It is a special purpose
bility octave band levels from 16 to 8,000 Hz.
Many sound level meters have the capability to
meter that may have, for example, Type 1 accu-
"A-weight" the octave band levels. The use of
racy and only an A-weighted filter. In this case, it
A-weighting is not appropriate for evaluating
would be described as Type S1A ("S" indicates
Special, "1" indicates Type 1 accuracy, and "A"
building mechanical systems.
a. Sound level meters. The American National
indicates A-weighted filter). The Type S meter
must carry a designation that describes its func-
Standards Institute (ANSI) provides specifications
for the acoustical and electrical response of sound
tion (such as Type S1A or Type S2C, etc.), and
must be constructed to meet the appropriate speci-
level meters. ANSI Standard S1.4 specifies four
fication applicable to that special combination.
types of sound level meters:
b. Octave band filters. ANSI standards also exist
Precision
Type 1
on the frequency limits and tolerances of octave
General Purpose
Type 2
Survey
band and one-third octave band sound and vibra-
Type 3
tion analyzers (ANSI S1.11). These filters are
Special Purpose
Type S
10-1
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