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Simpson Model 884-2
Sound Level Meter
OPERATOR’S MANUAL
SIMPSON ELECTRIC COMPANY 520 Simpson Avenue
Lac du Flambeau, WI 54538-0099 (715) 588-3311 FAX (715) 588-3326
Printed in U.S.A. Part No. 06-115307 Edition 6, 05/07
Visit us on the web at: www.simpsonelectric.com
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About this Manual
To the best of our knowledge and at the time written, the information contained in
this document is technically correct and the procedures accurate and adequate
to operate this instrument in compliance with its original advertised specifications.
Notes and Safety Information
This Operator’s Manual contains warning symbols which alert the user to check
for hazardous conditions. These appear throughout this manual where applicable, and are defined below. To ensure the safety of operating performance of
this instrument, these instructions must be adhered to.
Warning, refer to accompanying documents.
!
NOTES
Caution, risk of electric shock.
This instrument is designed to prevent accidental shock to the operator when
properly used. However, no engineering design can render safe an instrument
which is used carelessly. Therefore, this manual must be read carefully and completely before making any measurements. Failure to follow directions can result
in a serious or fatal accident.
Technical Assistance
SIMPSON ELECTRIC COMPANY offers assistance Monday through Friday
8:00 am to 4:30 pm Central Time. To receive assistance contact Technical Support or Customer Service at (715) 588-3311.
Internet: http://www.simpsonelectric.com
Warranty and Returns
SIMPSON ELECTRIC COMPANY warrants each instrument and other articles
manufactured by it to be free from defects in material and workmanship under
normal use and service, its obligation under this warranty being limited to making
good at its factory or other article of equipment which shall within one (1) year
after delivery of such instrument or other article of equipment to the original
purchaser be returned intact to it, or to one of its authorized service centers, with
transportation charges prepaid, and which its examination shall disclose to its
satisfaction to have been thus defective; this warranty being expressly in lieu of
all other warranties expressed or implied and of all other obligations or liabilities
on its part, and SIMPSON ELECTRIC COMPANY neither assumes nor authorizes any other persons to assume for it any other liability in connection with the
sales of its products.
This warranty shall not apply to any instrument or other article of equipment
which shall have been repaired or altered outside the SIMPSON ELECTRIC
COMPANY factory or authorized service centers, nor which has been subject to
misuse, negligence or accident, incorrect wiring by others, or installation or use
not in accord with instructions furnished by the manufacturer.
!
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7. Calibration
Adjustment: This screwdriver adjustment, located under a metal cap
on the side of the Instrument, is used to calibrate the 884-
2. The Simpson Sound Level Calibrator, Model 890-2, is
designed to calibrate the 884-2. The calibration procedures
are contained in the operator's manual for the 890-2.
8. Battery
Compartment: The battery compartment, which is totally separated from
the electronics, houses the battery.
4.3 Sound Level Measurements
To obtain sound level measurements with the 884-2:
a. Turn on the Instrument and select the desired measurement range. To en-
sure accurate results, check the battery every time sound level measurements are made.
b. When the Instrument is hand-held, orientate the microphone approximately
45° to 70° with respect to the horizontal plane and at an angle of 70° with
respect to incoming sound waves.
c. For OSHA compliance measurement set FAST/SLOW switch to SLOW and
the range switch to OSHA. Read exact dB(A) on red OSHA arc.
d. For other applications, select the desired range, weighting, and response. If
the meter fluctuations are in excess of 3 dB set the response to SLOW
position.
NOTE: With the range switch set to any of the other ranges (black numerals), the
black indicator, and the switch position corresponds to zero (0) indication. For
example, if switch is set to 90, and the indication is 5, add 5 to 90 to obtain 95 dB
level.
e. When not in use return the range switch to the OFF position and store the
Sound Level Meter in a safe place.
NOTES
4.4 Use With Auxiliary Equipment
The 884-2 is equipped with three outputs intended to be used with auxiliary
equipment such as a chart recorder, oscilloscope or the Simpson 898 Octave
Band Filter. These jacks are designed to give the operator more detailed and
comprehensive sound analysis study. The larger of the three jacks is designed to
be used with the Simpson 898 Octave Band Filter. The operator's manual for the
Model 898 describes how to use the 884-2 with this filter.
Non-Linear Distortion: At frequencies from 30 Hz to 50 Hz, the AC output will have
observable distortion with levels exceeding 0 dB on any meter range.
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Contents
1. INTRODUCTION ............................................................................... 7
1.1 General Description ...........................................................................7
1.2 Specifications .....................................................................................7
1.3 Items And Accessories Furnished With Instrument ............................ 9
1.4 Available Accessories ........................................................................ 9
2. INSTALLATION .................................................................................. 9
2.1 Unpacking And Inspection ................................................................. 9
2.2 Shipping ...........................................................................................10
2.3 Service .............................................................................................. 1 0
2.4 Battery Installation Or Replacement ................................................ 10
2.5 Installation ........................................................................................ 10
2.5.1 Tripod or Strap Mounting .................................................................. 10
2.5.2 Accuracy Of A Measurement .......................................................... 10
2.6 Care ..................................................................................................1 0
3. APPLICATION ................................................................................. 11
3.1 Decibel Scale ...................................................................................11
3.2 Measurement And Exposure Standards ..........................................11
3.3 Sound Fields ....................................................................................1 2
3.3.1 Free Field .......................................................................................... 12
3.3.2 Reverberant Field ............................................................................. 12
3.3.3 Semi-Reverberant Field ................................................................... 13
3.4 Microphone Orientation ....................................................................13
3.5 Effect Of Operator's Presence ..........................................................13
3.6 Windscreen.......................................................................................14
3.6.1 Loss of System Sensitivity Due to Windscreen .............................. 14
3.7 Meter Fluctuations ............................................................................ 14
3.8 Background Noise ............................................................................ 14
3.9 Dual Sound Sources ........................................................................15
4. OPERATING INSTRUCTIONS ......................................................... 16
4.1 Precautions.......................................................................................16
4.2 Operational Items And Features ...................................................... 1 6
4.3 Sound Level Measurements ............................................................18
4.4 Use With Auxiliary Equipment ..........................................................18
Slide Switch: This slide switch is used to select the response time of the
meter circuit as defined in Table 1-1.
3. BATT TEST A momentary push-button switch used to check the condition of the battery.
4. Microphone A condenser type microphone that converts sound energy vibrations into electrical signals.
5. Output Jacks
Decibel Output
Jack: A logarithmic output of 1.50 V DC is equivalent to meter
reading of +10 dB looking into 100 K⍀ load. The recommended plug of this jack is a Switchcraft #850.
RMS Output
Jack: A weighted or non-weighted output of 1.00 V RMS is equiva-
lent to a meter reading of +10 dB looking into a 100 K⍀
load. The recommended plug for this jack is a Switchcraft
#850.
External Filter
Jack: A non-weighted (flat response) output of 120 millivolts RMS
is equivalent to a meter reading of +10 dB looking into 100
K⍀ load. The recommended plug for this jack is a Switchcraft
#750.
6. Meter: A 0-100 µA DC full scale, taut-band movement contains a
dB scale with end markings of –10 dB and +10 dB and 1
dB divisions starting from –5 dB. The upper end of the
scale includes a BATT OK section.
4
5
6
7
130
O
S
120
H
O
A
F
F
Figure 4-1. Operational Items
3
and Features
8
4
17
50
BATT
TEST
60
SLOW
FAST
884-2
SOUND LEVEL METER
80
70
(OSHA)
TYPE S2A
100
110
0
9
1
2
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Table 3-2. Combining Noise Sources
Difference Between No. of dB to be Added to
Levels in dB Higher Level
0 3.0
2 2.1
4 1.5
6 1.0
8 0.6
10 0.4
4. OPERATING INSTRUCTIONS
This section contains the instructions required for the operation of the 884-2
Sound Level Meter. Follow these instructions carefully to obtain accurate and
useful data.
!
If noise levels exceed 115 dB(A) (SLOW response) immediate use of protective
ear muffs or plugs is required. According to the Occupational Safety and Health
Act of 1970, noise that measures above 115 dBA is automatically "too high" for
any length of exposure approximately over one second.
4.1 Precautions
a. Read Section 3 before performing measurements. This section contains im-
portant information on terminology, standards, techniques, and precautions
pertinent to sound and noise measurements.
b. Use the 890-2 Calibrator to check the calibration of the Sound Level Meter
periodically, especially if the Instrument has been subjected to severe mechanical shock or environmental extremes.
NOTES
4.2 Operational Items And Features
All items and features used to operate the 884-2 are described in Table 4-1 and
illustrated in Figure 4-1.
Table 4-1. Operational Items and Features
1. Range Switch This eleven position rotary switch is used to turn the Instrument on and to select the desired measurement range.
The range is indicated by the arrowhead. With the range
switch set to the "OSHA" position, the dB level is read on
the red arc displaying the OSHA range. With the range
switch set to one of the other dB ranges, the black arc is
used. A zero (0) indication on the black arc corresponds to
either 130, 120, 110, 100, 90, 80, 70, 60, or 50 dB as
determined by the position of the range switch. An indication other than zero (0) must be added to the range selected to obtain final level indication. For example, if the
range switch is set to the 110 position, and the indication is
+5, the sound level is 115 dB.
2. SLOW/FAST
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NOTES
mation can be made using Figure 3-4 and measurements of the background
noise alone and the sound source with the background noise. Simply take the
difference between these measurements and locate this difference value of the
abscissa of Figure 3-4. Move in a vertical direction from this point to the intersect
of the curve and then horizontally to the corresponding ordinate point. This ordinate point indicates a value to be subtracted from the total or sound source with
background noise measurement. The difference obtained represents the sound
source level. It should be noted that a difference of 3 dB or less between sound
source and background noise will provide only an indication of this sound source
level, not an accurate measurement.
10
9
8
7
6
5
4
3
2
1
0
dB CORRECTION (TO BE SUBTRACTED FROM TOTAL NOISE)
0
1
2
dB DIFFERENCE BETWEEN TOTAL NOISE &
BACKGROUND NOISE MEASUREMENTS
4
3
6 7
5
9
8
10
Figure 3-4. Background Noise Correction
3.9 Dual Sound Sources
When separate measurements are made on two sound sources, the combined
effect cannot be predicated by direct addition. For example: If two machines are
emitting equal noise levels of 80 dB, the combined level will be 83 dB, not 160 dB.
If the level of one source is 10 dB or greater than the other, the lower level source
can be disregarded as it will be "masked" by the higher level source. Information
listed in Table 3-2 can be used for calculating the combined effect of the two
sources. If more than two sound levels are involved, combine the highest two first,
then combine the total with the next highest remaining sound level. Continue this
procedure until all noteworthy levels are combined.
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3.6 Windscreen
When making measurements where wind is present, a low frequency interference can be introduced by air passing across the microphone. Try to make measurements where wind is not present; if this is not practical a windscreen should
be employed. When using this screen, indicated wind noise will be attenuated
approximately 20 dB. The loss of system sensitivity occurring with use of the
windscreen is shown in Figure 3-3.
NOTE: When making out-of-doors measurements, it is usually preferable to point
the microphone upward (to avoid interference from reflected high frequencies)
and as far from the body as is convenient.
+5
+4
+3
+2
+1
0
–1
–2
–3
–4
FREQUENCY RESPONSE ERROR DUE TO WINDSCREEN (dB)
–5
200
500
1000
FREQUENCY (Hz)
2000
5000
Figure 3-3. Loss of System Sensitivity Due to Windscreen
3.6.1 Loss of System Sensitivity Due to Windscreen
Grease and dirt on the windscreen will affect sound level measurements. To
check for dirt or grease on the windscreen, measure the level of continuous noise
indoors with or without the windscreen in place. To clean the windscreen, wash
with a mild detergent. Thoroughly rinse and dry before placing over microphone.
3.7 Meter Fluctuations
If the meter indication fluctuates more than 3 dB, set the meter response switch of
the Instrument to the SLOW position unless otherwise specified in the applicable
specification. Then, if the fluctuations are less than 6 dB, record a value of 3 dB
less than maximum indication. Infrequent, high peaks customarily are disregarded.
(When making noise survey measurements record the highest peak.)
NOTE: As pointed out in Table 3-1, applicable standards require SLOW meter
response when making noise surveys.
3.8 Background Noise
Ideally, any sound source being measured should be isolated from effects due to
extraneous or background noise. If the background noise is 10 dB or more below
the sound source level desired, the effect from the background noise can be
considered negligible. In instances where the ratio is less than 10 dB, an approxi-
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10,000
1. INTRODUCTION
1.1 General Description
The Simpson 884-2 Sound Level Meter (hereafter referred to as the 884-2 or the
Instrument) is a portable, general purpose sound level instrument, capable of
accurate sound level measurements over a range of 40 to 140 dB. This encompasses the noise level of a quiet residence to that beyond the threshold of pain.
This dB range is compatible with current Federal, State, and local noise ordinance requirements; including safety and environmental noise checks.
The 884-2 meets the requirements of the American National Standards Institute
(ANSI) Standard Specification S1.4 - 1983 for "Type S2A General Purpose Sound
Level Meters and the International Electro- Technical Commission (IEC) 651." It
can be used by industry to measure noise levels to comply with Occupational
Safety and Health Act of 1970 (OSHA) and the Walsh-Healy Act, except for direct
measurement of impact (impulse) noise.
The 884-2 can be hand-held for rapid testing or mounted on a tripod for measurements over extended periods of time. The meter case is constructed of highimpact molded plastic, especially contoured at the microphone end to minimize
reflections of the sound energy field being measured.
The 884-2 is equipped with a range selector switch which references the 0 dB
point of the indicating instrument to the range selected. For example, when the
range switch is set to 70, the zero (0) mark on the black arc is equal to 70 dB. Fast
or slow meter response is switch selectable.
The 884-2 offers three outputs which are proportional to the sound level input: a
RMS output, a dB output, and an external filter output that is compatible with the
Simpson 898 Octave Band Filter.
1.2 Specifications
The specifications for the 884-2 are listed in Table 1-1.
Table 1-1. Specifications
1. Microphone: The microphone is a condenser type with the size as
type L per ANSI S1.12-1967. The nominal electrical
impedance is 350V, 20% @ 23°C. The microphone is
omnidirectional; its angle of incidence which approximates random incidence response is 70°.
2. Sound Level: Measurement Ranges: 40 dB to 140 dB. Zero (0) dB
reference is 20 µPascals. :Maximum SPL: 140 dB SPL
for linearity within 1 dB.
3. Accuracy: Meets ANSI S1.4-1983 for a Type S2A instrument.
4. Weighting: Conforms to the A-weighting characteristic specified
in ANSI S1.4-1983. The "External Filter" jack may be
used to obtain a flat response.
5. Meter: Pivot and Jewel movement with 2-1/2" dial having
end markings of –10 dB and +10 dB, and fifteen 1 dB
scale markings. From –5 dB to +10 dB the accuracy
specification for a Type S2A instrument.
6. Speed of Response:
Types of response: Selectable "Slow" or "Fast" modes provide the
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PLANE OF
MICROPHONE
AXIS OF
MICROPHONE
VERTICAL ANGLE
(45˚ – 70˚)
response times required by the ANSI specification for
a Type S2A instrument.
SLOW Response: Response to a 500 millisecond tone burst of 1000 Hz
is nominally 2.5 dB down from a reference steady
state signal at the same level and frequency. Overshoot response to a suddenly applied steady state
signal is less than 0.5 dB. When an applied signal is
tuned off, the decay rate is less than 3 seconds per 10
dB.
FAST Response: Response to a 200 millisecond tone burst of 1000 Hz
is nominally 2.0 dB down from a reference steady
state signal at the same level and frequency. Overshoot response to a suddenly applied steady state
signal is less than 0.5 dB. When an applied signal is
tuned off, the decay rate is less than 0.5 seconds per
10 dB
7. Linearity: Primary indicator range is from 0 dB to +10 dB on
each range. Overall indicator range is –5 dB to +10
dB. The dedicated "OSHA" range primary indication
is +105 dB to +115 dB, with an overall indication of
+100 dB to +115 dB. Within these limits, the primary
indicator accuracy is 1 dB and the overall accuracy is
1.5 dB.
8. Calibration: Recommended calibration frequency is 1000 Hz at
sound pressure levels of either 94 dB on the 90 dB
range, or 114 dB on the 110 dB range. Screwdriver
adjustable from the side of the case.
9. Output Connections: This Instrument is provided with three outputs: External Filter, RMS Output, and dB Output.
External Filter: Provides non-weighted (flat response) output of 120
mV RMS, at meter reading of +10 dB, into a 100 KV
load; a lower impedance may affect the meter reading. This output is not affected by the "Fast-Slow" setting. The recommended plug is Switchcraft's #750
(0.141" diameter).
RMS Output: Provides weighted or non-weighted output of 1.00 V
RMS, at a meter reading of +10 dB, into a 100 KV
load; a lower impedance will not affect the meter reading. This output is not affected by the "Fast-Slow" setting. The recommended plug is Switchcraft's #850
(0.097" diameter).
dB Output: Provides logarithmic output of +1.50 V DC, at a meter
reading of +10 dB, into a 100 KV load; a lower impedance will not affect the meter reading. The response
time of this output is set by the "Fast-Slow" setting. The
exponential-time-averaging time constant is per ANSI
S1.4-1983, paragraphs 6.2 and 6.3: Slow is 1000
milliseconds, and Fast is 125 milliseconds. The recommended plug is Switchcraft's #850 (0.097" diameter).
10. Power
Requirements: One 9-volt alkaline battery, NEDA 1604A (or equal)
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3.3.3 Semi-Reverberant Field
This field is most common and exists whenever the sound level being measured
contains a significant amount of both reflected and direct sound waves.
3.4 Microphone Orientation
When making measurements in a free or semi-reverberant field, orient the microphone so that the angle of incidence, formed by incoming sound waves and axis
of the microphone, is equal to the random incidence angle of the microphone. For
the 884-2 this angle is 70° (refer to Figure 3-2).
When making measurements in a reverberant field, orientation of the microphone is not critical. However, it is recommended, where possible, that the operator use the same orientation (70°) as for the free or semi-reverberant field.
Vertical orientation of the microphone is not critical except where it is in line with
a second sound source or a high-amplitude reflection of a sound source. It usually is invalidated by a second sound source, or by a nearby reflecting surface.
When evaluating a particular sound source, avoid holding the microphone in
such a way that the reading is invalidated by a second sound source, or by the
proximity of a nearby reflecting surface.
3.5 Effect Of Operator's Presence
When sound is coming mainly from one
direction, the reading might be affected
by the relative positions of the microphone
and operator. For example, if the operator
and microphone are in line and facing
the sound source, there can be a marked
increase in response at high frequencies
because the operator will act as a reflector and produce errors of several dB at
frequencies above 100 Hz. A more uniform frequency response is obtained with
the Instrument extended as far as conveniently possible in front of the operator,
and the axis of the microphone oriented
to form an angle of incidence of 70° with
the incoming sound wave. Do not point
the Instrument toward a source of noise
other than the one being measured.
The 884-2 (or its microphone) can be
mounted on a tripod for further reduction
in the effects of the operator's presence.
A practical arrangement is to tilt the microphone axis at an angle of approximately 45° to 70° with respect to the horizon. This allows the operator to step back
several feet or completely away and still
be able to make measurements.
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Figure 3-2. Orientation of
Microphone and Operator with
respect to Incoming and Sound
Waves
PLANE OF
MICROPHONE
Top View
Side View
SOUND SOURCE
ANGLE OF
INCIDENCE (70˚)
AXIS OF
MICROPHONE
INCOMING
SOUND WAVE
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also have defined allowable noise (undesirable sound energy) level exposure
limits for persons in industrial environments. Selected and applicable parts of
those currently in force are cited in this manual. Standards and government regulatory laws are subject to modification or expansion. Check for latest available
documents and information.
The specification for a Type S2A instrument takes into account the average response of the human ear which varies as a function of the intensity of sound. It
groups intensity into three weighting curves: "A", "B" and "C". The "A" weighted
curve more closely corresponds to the human ear at the low sound levels.
As indicated in Figure 3-1, the "B" and "C" weighting curves include more of the
low frequency information. Thus, at any level, measurements taken with various
weightings can be compared in determining the frequency content of the noise.
This is done by indicating the level in dB, accompanied by the weighting letter
notation "A", "B" or "C", preferable in parenthesis; e.g., the 100 dB(A), etc.
The allowable employee noise level exposure limits are established by the Occupational Safety and Health Act of 1970 (OSHA), the Walsh-Healy Act (Federal
Register, Volume 34, No. 96) and paragraph 1910.95 of the Occupational Safety
and Health Standards (Federal Register, Vol. 36, No. 105, May 29, 1971) and the
OSHA Hearing Conservation Program Amendment, Federal Register, Vol. 46,
No. 162, August 21, 1981. Table 3-1 summarizes these limits.
*Table 3-1. Permissible Noise Exposure Limits
Duration per Day Sound Level, dB(A) SLOW
In Hours Response
32 80
16 85
8 90
6 92
4 95
3 97
2 100
1-1/2 102
1 105
1/2 110
1/4 or less 115
*From Federal Register, Vol. 46, No. 162, August 21, 1981.
will typically provide 40 hours of continuous operation.
11. Temperature
Range: Operating temperature is –10°C to +50°C.
Storage
Temperature: –40°C to +60°C with the battery removed.
12. Temperature
Influence: Typically 0.015 dB/°C at 1kHz.
13. Operating Humidity: 0 to 90% relative humidity (non-condensing) for
a reading change of < 0.5 dB.
14. Warm-up Time: Approx. 30 seconds.
1.3 Items And Accessories Furnished With Instrument
All items required to operate the 884-2 are furnished with each Instrument, and
are listed in Table 1-2.
Table 1-2. Accessories Furnished with Instrument
Qty. Description Part Number
1 9-volt battery NEDA 1604A*
1 Operator's Manual 6-115307
*Available from local retail stores.
1.4 Available Accessories
Table 1-3. Available Accessories
Description Part/Catalog Number
Screwdriver 5-116470
Windscreen 00197
Calibrator, 890-2 12890
Package Case 10-866065
Adapter, Microphone to Tripod 00184
898 Octave Band Filter Set 02231
2. INSTALLATION
3.3 Sound Fields
3.3.1 Free Field
A free field contains no reflecting objects. Ideally it prevails around a point sound
source located in free space. However, it can be considered to exist whenever the
sound level being measured is caused mainly by sound waves coming directly
from the sound source. This can occur even if there are reflecting objects, if
measurements are made close to the sound source.
3.3.2 Reverberant Field
A reverberant field contains reflecting objects and the sound level being measured is caused mainly by reflections of the sound source. This usually occurs at
a moderate distance from the sound source.
12
This section contains information and instructions for the packaging and shipping of the 884-2. Included are procedures for unpacking and inspection, service,
shipping, battery installation, installation and care.
2.1 Unpacking And Inspection
Examine the shipping carton for obvious signs of damage. If shipping carton is in
good condition, inspect the Instrument for possible damage incurred during shipment. If damaged, notify the carrier and supplier and do not attempt further use of
the Instrument. If the Instrument appears to be in good condition, read the Operator's
Manual in its entirety. Become familiar with the Instrument in the manual, then
proceed to check the electrical performance as soon as possible. Save the shipping carton and packing materials for future storing or shipping of the Instrument.
9
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2.2 Shipping
Pack the Instrument carefully and ship it prepaid to the proper destination. Insure
the Instrument.
2.3 Service
This Instrument contains no operator serviceable parts, except for the battery.
Refer all service requests to the Simpson factory. If the Instrument is covered by
warranty, include the model number, serial number, and date of purchase.
2.4 Battery Installation Or Replacement
The 884-2 is powered by a 9-volt alkaline battery. The battery is packaged separately. To install or replace the battery:
a. Turn the range switch to the "OFF" position.
b. Using a screwdriver or coin, loosen the two screws located on the battery
cover access compartment and remove the cover.
c. Install or replace the battery with the connector on the left side of the Instru-
ment. Route the cable between the battery and upper wall of the battery
compartment.
2.5 Installation
The Instrument, when in operation, may be either hand-held or mounted on a
tripod. The physical position of the Instrument does not affect the accuracy.
2.5.1 Tripod or Strap Mounting
The 884-2 can be attached to any commercial, photography-type tripod having a
standard 1/4-20" mounting screw. The mounting screw is aligned with the threaded
insert in the case and finger-tightened. A camera-type carrying strap can be
attached to the threaded insert. Carry the Instrument with the strap around the
wrist to prevent accidental dropping.
2.5.2 Accuracy Of A Measurement
The accuracy of a measurement will be affected by several factors, one of which
is the position of the microphone with respect to the sound source. Read Section
3 carefully for general background information. (See Section 4 for operating instructions for obtaining correct data from the measurements.)
2.6 Care
a. Immediately clean any spilled materials from the Instrument and wipe dry. If
spillage is corrosive, use a suitable cleaner to remove it and to neutralize
corrosive action.
b. To protect the microphone, keep sharp objects away from the top. Never rest
the unit on the microphone. If the microphone is detached, always lay it on its
side.
c. Whenever the Instrument is not in use, set the range switch to the OFF posi-
tion.
d. Avoid prolonged exposure or usage in areas subject to temperature and
humidity extremes, vibration, mechanical shock, dust, corrosive fumes, and
10
strong electrostatic and electromagnetic interference.
e. Verify Instrument calibration with a 890-2 Acoustical Calibrator.
f. It is recommended that the Instrument be returned to the factory annually
(sooner if required) for a complete overall check, adjustment, and calibra-
tion.
g. When the Instrument is not in use store it in a room free from temperature
extremes, dust, corrosive fumes, mechanical vibration or shock. If storage
time is expected to exceed 30 days, remove the battery.
3. APPLICATION
This section contains basic information required for effective application of the
884-2 Sound Level Meter, and must be understood before attempting to operate
the Instrument for the first time.
3.1 Decibel Scale
The human ear has a mid-frequency dynamic sound sensitivity range of greater
than one million to one, from the lowest level that can be detected to the highest
that can be tolerated without pain. Because of the large ratio of value involved, a
linear meter scale marked in pressure units becomes impractical. A scale based
on logarithms, called a decibel (dB) scale, is used. This scale expresses the ratio
between the sound pressure level being measured and a reference. This simplifies notation and manipulation by reducing large ratios into smaller convenient
numbers. For example, a million-to-one pressure ratio can be expressed on a 0 to
120 dB scale.
3.2 Measurement And Exposure Standards
The American National Standards Institute (ANSI), in collaboration with scientific
and engineering societies, has established a standard, S1.4-1983, for conformance of all approved sound level meters. Federal, state and local governments
+5
0
–5
–10
–15
–20
–25
–30
–35
RELATIVE RESPONSE DECIBELS
–40
–45
–50
20 50 100
C
B
FREQUENCY RESPONSES
FOR SLM WEIGHTING
CHARACTERISTICS
A
1000 2000
500
200
FREQUENCY (Hz)
Figure 3-1. A, B, and C Weighted Responses of the Sound Level Meter
11
A
B AND C
5000
10,000
20,000
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