ASSESSING THE IMPACT OF AIR-CONDITIONING OUTDOOR SOUND LEVEL by Navid Anari

1997 GUIDELINE for ASSESSING THE IMPACT OF AIRCONDITIONING OUTDOOR SOUND LEVELS IN THE RESIDENTIAL COMMUNITY

Guideline L

4301 NORTH FAIRFAX DRIVE

ARLINGTON, VIRGINIA 22203

IMPORTANT

SAFETY RECOMMENDATIONS It is strongly recommended that the product be designed, constructed, assembled and installed in accordance with nationally recognized safety requirements appropriate for products covered by this guideline. ARI, as a manufacturer's trade association, uses its best efforts to develop guidelines, employing state-of-the-art and accepted industry practices. However, ARI does not certify or guarantee safety of any products, components or systems designed, tested, rated, installed or operated in accordance with these guidelines or that any tests conducted under its guidelines will be non-hazardous or free from risk.

Note: This guideline supersedes ARI Guideline L-1992.

Price $10.00 (M) $20.00 (NM) Printed in U.S.A.

TABLE OF CONTENTS

SECTION

PAGE

Section 1.

Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Section 2.

Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Section 3.

Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Section 4.

Tutorial on Sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Section 5.

Human Response to Sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Section 6.

Establishing Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Section 7.

Use of ARI Standards 270 and 275 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Section 8.

Preplanning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Section 9.

Corrective Measures (On-Site) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Section 10.

Special Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Section 11.

Determination of Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

TABLES Table 1.

National Estimate of Outdoor Background Noise Based on General Type of Community Area and Nearby Automotive Traffic Activity . . . . . 4

Table 2.

Sample Calculations for Example for ARI Standard 275 . . . . . . . . . . . . . 8

Table 3.

Tolerance, A-Weighted dB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

FIGURES Figure 1.

Community Response as a Function of Sound Pressure Level . . . . . . . . . . 3

Figure 2.

Estimated Outdoor Background Sound Pressure Levels as a Function of Community Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 3.

Cost Trend as a Function of Required Sound Pressure Level . . . . . . . . . . 5

Figure 4.

Example of Installation with No Barrier and One Reflective Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

APPENDICES Appendix A.

References - Normative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Appendix B.

References - Informative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Appendix C.

A-Weighted Adjustments as a Function of Frequency . . . . . . . . . . . . . . . . 10

ARI GUIDELINE L-1997

ASSESSING THE IMPACT OF AIR-CONDITIONING OUTDOOR SOUND LEVELS IN THE RESIDENTIAL COMMUNITY Section 1. Purpose 1.1 Purpose. The purpose of this guideline is to provide an educational document to be used by municipal planners or others as a guide in assessing the impact of outdoor airconditioning sound levels and to assist in the establishment of recommended outdoor sound levels for the residential community. 1.1.1 Intent. This guideline is intended for the guidance of the industry, including manufacturers, engineers, municipal planners, regulators and users. 1.1.2 Review and Amendment. This guideline is subject to review and amendment as technology advances.

Section 2. Scope 2.1 Scope. Subjects which will be covered in this guideline include: a. b. c. d. e. f. g. h. 2.2

Tutorial on Sound Human Response to Sound Establishing Criteria Use of ARI Standards 270 and 275 Preplanning Corrective Measures (on-site) Special Considerations Determination of Compliance

Exclusions. 1. 2.

This guideline does not recommend specific acceptable sound levels. Areas other than residential are not included (i.e., commercial applications except as they impact on the residential community).

Section 3. Definitions 3.1 Definitions. All terms in this document will follow the standard industry definitions established in the current edition of ASHRAE Terminology of Heating, Ventilation, Air Conditioning and Refrigeration, unless otherwise defined in this section.

3.2 Ambient Noise (Background Noise). All encompassing noise associated with a given environment, being usually a composite of sounds from many sources near and far. 3.3 Decibel (dB). Dimensionless number expressing, in logarithmic terms, the ratio of a quantity to a reference quantity. For acoustical work it is used to express levels of sound power and sound pressure. 3.4

Hertz (Hz). Unit for frequency in cycles per second.

3.5 Octave Band. An octave band is a band of sound covering a range of frequencies such that the highest is twice the lowest. The octave bands used in this standard are those defined in ANSI Standard Sl.ll . 3.6 One-Third Octave-Band. A one-third octave band is a band of sound covering a range of frequencies such that the highest frequency is the cube root of two (approximately 1.26) times the lowest. The one-third octave bands are those as defined in ANSI Standard Sl.ll . 3.7 Sound Level Meter. A device used to quantify sound pressure levels. A meter meeting the requirements of the Type 1 precision meter described in ANSI Standard S1.4. 3.8 Sound Power Level. The sound power level (Lw) of a sound source, in decibels (dB), is ten times the Logarithm to the base 10 of the ratio of the sound power radiated by the source to a reference power. The reference power used in this guideline is 1 picowatt (lpw). Sound power levels are not affected by environment or distance. 3.8.1 A-weighted Sound Power Level. Logarithmic summation of A-weighted octave band or one-third octave band sound power levels. 3.9 Sound Pressure Level. The sound pressure level in decibels (dB), of a sound is 20 times the logarithm to the base 10 of the ratio of a given pressure to a reference pressure. The reference pressure used in this guideline is 20 micropascals, (Pa). Sound pressure levels are affected by environment or distance. 3.9.1 A-weighted Sound Pressure Level. Logarithmic summation of A-weighted octave band or one-third octave band sound pressure levels.

ARI GUIDELINE L-1997 3.10 Sound Rating Level. That number which is assigned to equipment rated in accordance with ARI Standard 270 3.10.1 Standard Sound Rating Level. That number assigned to equipment rated in accordance with ARI Standard 270 at Standard Rating Conditions. 3.10.2 Application Sound Rating Level. A number assigned to equipment rated in accordance with ARI Standard 270 at conditions other than Standard Rating Conditions. 3.11 Tone. A sound wave capable of exciting an auditory sensation having pitch.

Section 4. Tutorial on Sound 4.1 Sound may be defined as any pressure variation that the human ear can detect. These pressure variations travel through air, like ripples in a pond, radiating from a source and arriving at the listener's ear. Sound (pressure variations) has both frequency and amplitude components. Together, these components determine the character of the sound. Frequency is measured in Hertz (Hz) (cycles per second). The frequencies that are important to the average person range from 20 Hz to 10,000 Hz. It is not practical to attempt to measure pressure amplitude at each discrete frequency, within this range, therefore the range is divided into octave or one-third octave frequency bands. The American National Standards Institute (ANSI) specifies the frequencies which define these octave and one-third octave bands (ANSI Standard Sl.11 ). The amplitude of pressure fluctuations that the typical human ear can detect ranges from 20 decibels (dB) to 140 dB. The decibel scale for sound pressure is a logarithmic scale with 0 dB equal to a reference pressure of 20 micropascals (MPa). People hear sounds most readily when the predominant sound energy occurs at frequencies between 1000 and 6000 Hz. To measure sound on a scale that approximates the way it is heard by people, more emphasis or weight is given to the frequencies that humans hear more easily. To arrive at this approximation of the response of the human ear, the Aweighted measurement scale was developed. Adjustments are made to the measured dB values in each frequency band to arrive at these A-weighted dB values. ANSI Standard S1.42 specifies these adjustments as a function of frequency. A table illustrating the adjustments can be found in Appendix C.

Section 5. Human Response to Sound 5.1 An individual's reaction to a given sound is very subjective and can depend upon many parameters such as mood, time of day, activity and type of sound. For example, the sound of music can be acceptable under some circumstances and unacceptable or annoying under others. Also, an individual's association between a given sound and some unpleasant event may increase their level of intolerance to that sound. The amplitude or loudness of a sound can contribute to its annoyance level but that would depend upon the circumstances. For example, a 60 dB sound level may be acceptable in some residential areas and unacceptable in others due to such things as background noise levels (i.e., traffic or airport noise). The frequency of a sound is also important. High frequencies (usually above 1,000 Hz) may be considered annoying, particularly when the content of the sound is tonal in character. Annoyance generally increases as tones rise in frequency although it has also been found that frequencies below 100 Hz can also be annoying. An intermittent or irregular sound can be particularly distracting. For example, equipment rapidly cycling on and off or producing a modulating sound could be considered objectionable.

Section 6. Establishing Criteria 6.1 The primary reason for establishing sound ordinances and defining acceptance criteria is to create and maintain a pleasant environment in which to live. This means that the criteria must be low enough to minimize community complaints, yet be high enough to minimize installation costs. Figure 1 illustrates the expected community response as a function of sound level. Although specific sound levels are not identified, it is obvious that as the sound level goes up, so do the complaints. The following examples illustrate methods by which practical acceptance criteria may be established: 6.2 Criteria Based on Existing Ambient Sound Levels. Some communities and cities establish ordinance levels with respect to the ambient background sound level. One such ordinance defines the acceptability of a sound in terms of how much it exceeds the background noise as follows: a. Exceeding ambient sound level by more than 15 dB(A) constitutes a nuisance, action required.

ARI GUIDELINE L-1997 b. Exceeding ambient sound level by 10 - 15 dB(A) could be considered as a nuisance and action should be taken to improve the situation. c. Exceeding ambient sound level by 5 - 9 dB(A) is of marginal significance. d. Exceeding ambient sound level by less than 5 dB(A) is acceptable. The advantage of this method is that the criteria puts attention where it is most needed which is specifying acceptable sound levels relative to the background sound. The main disadvantage is that the background sound must be evaluated accurately through on-site measurements before the ordinance is drafted. Care must also be exercised when using this method so that a practical limit will be established in those areas where the background levels are very low. In such situations it is possible to cite a sound level in the ordinance which cannot be achieved with sound levels generated by state-of-the-art air-conditioning equipment. When this occurs, the costs to bring the equipment into compliance can be prohibitive and enforcement of the ordinance can be very difficult. This will be discussed further in the section on establishing practical criteria. When measured background sound levels are not available, Table 1 and Figure 2 may be used to estimate background sound levels for different types of environments and conditions. It is strongly recommended, however, that measured levels be used as the basis for establishing criteria.

6.3 Criteria Based on Zone Concept. Sound ordinance levels may also be set by specifying the maximum allowable A-weighted level at the property line or border of the zone. For example, zones could be classified into - Heavy Manufacturing, General Manufacturing, Restricted Manufacturing, Business and Commercial, Residential Urban, Residential Suburban, Residential Rural, and Harbors and Waterways. The allowable sound level at a residential zone boundary depends upon the classification of the adjacent zone and is selected accordingly. The advantage of this type of sound ordinance is that uniform limits can be set. Estimated A/C equipment sound levels can be calculated to check for compliance before the installation. The establishment of practical criteria limits is extremely important. Figure 3 depicts the trend of increasing cost to achieve lower property line sound levels. Some of the repercussions of setting ordinance sound levels too low are; shutting down operation of air-conditioning units (angry owners), larger lot sizes, relocation of units, expensive noise control measures, and finally, the added enforcement costs. Each community must determine its own particular characteristics in order to include all of the important factors so that the ordinance is realistic and practical in terms of both sound levels and cost. A consultant may be required to help with the more complex situations.

Community Response

VIGOROUS LEGAL ACTION THREATS OF LEGAL ACTION STRONG COMPLAINTS

AVERAGE EXPECTED RESPONSE

MILD COMPLAINTS MILD ANNOYANCE

RANGE OF EXPECTED RESPONSES FROM NORMAL POPULATION

NO ANNOYANCE

HIGH

LOW Sound Pressure Level

Figure 1. Community Response as a Function of Sound Pressure Level

ARI GUIDELINE L-1997 Table 1. National Estimate of Outdoor Background Noise Based on General Type of Community Area and Nearby Automotive Traffic Activity No.

Condition

Curve No. in Figure 2

Nighttime, rural; no nearby traffic of concern

Daytime, rural; no nearby traffic of concern

Nighttime, suburban; no nearby traffic of concern

Daytime, suburban; no nearby traffic of concern

Nighttime, urban; no nearby traffic of concern

Daytime, urban; no nearby traffic of concern

Nighttime, business or commercial area

Daytime, business or commercial area

Nighttime, industrial or manufacturing area

Daytime, industrial or manufacturing area

Within 300 ft. [91.4 m] of intermittent light traffic route

Within 300 ft. [91.4 m] of continuous light traffic route

Within 300 ft. [91.4 m] of continuous medium-density traffic

Within 300 ft. [91.4 m] of continuous heavydensity traffic

300 to 1000 ft. [91.4 to 304.8 m] from intermittent light traffic route

300 to 1000 ft. [91.4 to 304.8 m] from continuous light traffic route

300 to 1000 ft. [91.4 to 304.8 m] from continuous medium-density traffic

300 to 1000 ft. [91.4 to 304.8 m] from continuous heavy-density traffic

1000 to 2000 ft. [304.8 to 609.6 m] from continuous medium-density traffic

1000 to 2000 ft. [304.8 to 609.6 m] from continuous heavy-density traffic

Section 7. Use of ARI Standards 270 and 275 7.1 A well-planned community sound ordinance will establish acceptable sound levels which any new or replacement construction must meet. Within the airconditioning industry, ARI Standard 270, is widely accepted as the preferred procedure for determining the sound rating level of the outdoor sections of residential size unitary equipment. ARI Standard 275, describes a procedure for applying these sound rating levels to practical real-life situations. Through the use of ARI Standard 270 and ARI Standard 275, the contractor, developer, or homeowner can estimate whether the equipment to be installed will meet an existing sound specification. If the predicted level is too high there are several options available, however, the number of options become quite limited once the air-conditioning unit is installed. In order to use ARI Standards 270 and 275 to their best advantage, a thorough understanding of each of these Standards is recommended. ARI Standard 275 provides a procedure for converting the published ARI Sound Rating Level (SR) number which is a tone-corrected, A-weighted sound power level (determined in accordance with ARI 270) into a tone corrected, A-weighted sound pressure level for a specific installation. This procedure accounts for major acoustical factors such as distance, reflecting walls, and sound barriers. Several alternate locations can be evaluated for the impact of sound on neighbors before actual installation of the equipment results in a problem. If there appears to be a problem during the planning stage, then the options still include choosing an alternate location, a quieter air conditioning unit, and/or the application of several methods of noise control. Municipal planners can use the ARI Directory and ARI 275 to help establish reasonable property line noise ordinances and perhaps recommend minimum lot size* or set back distances to help minimize the impact of equipment sound levels. *

See section on Preplanning

ARI GUIDELINE L-1997 80 70 60 50 40

7 6 5 4 3 2 1

60.5 55.5 50.5 45.5 40.5 35.5

30 20

30.5

Curve No. 7 6 5 4 3 2 1

0 63

125

250

500

1000

2000

4000

8000

Octave Band Center Frequency, Hz

Curve No. 1 = 30.5 dB(A) Curve No. 2 = 35.5 dB(A) Curve No. 3 = 40.5 dB(A) Curve No. 4 = 45.5 dB(A) Curve No. 5 = 50.5 dB(A) Curve No. 6 = 55.5 dB(A) Curve No. 7 = 60.5 dB(A) Figure 2. Estimated Outdoor Background Sound Pressure Levels as a Function of Community Area

Figure 3. Cost Trend as a Function of Required Sound Pressure Level

ARI GUIDELINE L-1997 The use of ARI Standard 275 is perhaps best illustrated through the following example: Example Figure 4 shows an outdoor unit located 5 ft. [1.5 m] from the side of a house, and 15 ft. [4.6 m] back from the property line. There are no barriers and there is one reflective surface. The air conditioner sound levels will be estimated for three locations. These locations represent a backyard patio 47 ft. [14.3 m] away, the property line 15 ft. [4.6 m] away, and just inside an open window 35 ft. [10.7 m] away. The Sound Rating Level for the unit in this example is 80 dB. The calculations are shown in Table 2 as follows: 1. Start with the equipment sound power rating. 2. Add 3 dB Equipment Location Factor from Table 1, Item 1 of ARI 275 to account for the sound energy reflected back from the wall next to the unit. 3. Add zero for the Barrier Shielding Factor from Table 1, item 2 of ARI 275 since there is no acoustical barrier in this example. 4. Add zero, zero, and 10 dB respectively for the Three points, for the Sound Path Factor of Table 1, item 3 in ARI 275 since there are two clear sound paths and one open window. If the window were closed the Sound Path Factor would be 17 dB instead of 10 dB. 5. Add the Distance Factor from Table 2 of ARI 275 for the three different distances: 31 dB, 21 dB, and 28 dB for distances of 47, 15, and 35 ft. [14.3, 4.6 and 10.7 m] respectively. This converts sound power to sound pressure for each distance. 6. Combine all of the levels and factors to obtain the estimated A-weighted sound pressure levels at the three evaluation points : 52 dB, 62 dB and 45 dB. The ARI 275 application standard also gives detailed examples of other installations that involve most typical application factors that are likely to be encountered.

Section 8. Preplanning 8.1 Once the aforementioned procedures are understood, it is a rather straight forward extension to use ARI 275 to back-calculate acceptable lot sizes based on an existing community sound ordinance or to develop/modify a practical community sound ordinance based on existing available equipment sound levels. For example, consider evaluation point #2 from the preceding example. If the community sound ordinance specified a level not to exceed

65 dB(A) at the property line, a unit with an ARI Sound Rating Level of 80 dB would be acceptable. However, if the ARI guide indicates that typical sound rating levels for the type of equipment to be installed averages 86 dB, the target sound level would not be achieved. In this situation, possible solutions include: 1. Increasing lot sizes such that the distance factor provides sufficient attenuation to achieve the desired sound level. 2. Modifying the sound ordinance to recognize the fact that practical limitations on lot size and equipment design will not permit the original goal to be met. 3. Selecting quieter equipment which typically is more expensive. 4. Treating the equipment on-site to achieve the desired sound level. This generally requires the expertise of an acoustical consultant. Although ARI Standards 270 and 275 do not specifically recommend a piece of equipment or equipment location to achieve a specified sound level, they do provide the information needed to make an intelligent, informed decision on selection of equipment. Preplanning is also important when drafting a building code to prevent unit placement in an offending area. For example, the building code could state that the outdoor unit cannot be placed within 15 ft. [4.6 m] of a neighbor's bedroom window. This alerts the builder of a subdivision that the houses must be designed with this in mind. Also, this restriction in the code would be known by installing contractors in the area so that add on installations would also meet the code.

Section 9. Corrective Measures (On-Site) 9.1 As previously mentioned, once the equipment is installed, the number of options available to achieve a specified sound level become limited and should involve the services of an acoustical consultant. Perhaps the most typical form of corrective action involves a total or partial sound enclosure or barrier. These devices are generally constructed such that they absorb, block, or redirect the sound or some combination of the three. It is extremely important that the use of such devices not alter the normal operation of the equipment being treated. It is also very important that a thorough understanding of the problem be reached before a design is selected. Relatively minor mistakes in a design can result in only a fraction of the estimated attenuation being achieved.

ARI GUIDELINE L-1997 Another type of corrective action is modification of the dwelling. Single pane windows can be replaced with dual or triple pane windows. Also, storm windows or storm doors could be added for a degree of sound reduction. In an extreme case, a masonry wall could be added to the side of a dwelling for a noise barrier. Before any corrective measures are taken, however, an acoustical consultant should analyze the situation. A consultant could analyze the existing situation and recommend the appropriate corrective action. For example, he may recommend possible modification of windows, doors, or walls that would give a greater transmission loss depending on the nature of the offending noise.

Section 10. Special Considerations 10.1 There are some types of housing which can pose significant problems when trying to establish a reasonable outdoor sound ordinance. Typically, these types of housing are of higher density than the normal residential community. For example, a town-house may be in an urban setting where the houses are built very close to property lines. An air-conditioning unit on the side of a house may be only 6 ft. [1.8 m] away from a neighbor's window and even with a low sound rating level, could easily exceed a property line sound level based on more typical residential community lot sizes. A property line sound level for town homes might not be sufficient to avoid complaints. In these situations, a change to the building code might be necessary to prevent unit placement in an area which would be particularly offensive to a neighbor.

47 ft. [14.3 m]

Residence 15 ft. [4.6 m]

These two types of housing or other high density situations are extremely complex and it is recommended that the services of an acoustical consultant be considered before guidelines are drawn up for a community.

Section 11. Determination of Compliance 11.1 As with any type of ordinance or specification, there must be a means of determining compliance. When dealing with sound, compliance is generally determined through on-site measurements made with a hand held sound level meter. Recommended meters fall into two types, each with its own measurement tolerance, or accuracy. Within each type, meters exist which provide the user with either overall dB(A) sound levels, octave band sound levels, or one-third octave band sound levels. The sound level meter is selected such that it provides the accuracy needed and the data needed in the format specified in the ordinance. More information on sound level meters can be obtained in ANSI Standard S1.4 . The highest level of accuracy is attained with the Type 1 meter which is termed a "precision instrument." Type 2 is for general purpose measurements.

#1 5 ft. [1.5 m]

Low rise apartment buildings can also pose difficult problems. Two and three story apartment buildings can have individual air conditioning units for each apartment. As a possible solution in southern areas, these apartment buildings can be built with a flat roof, and all outdoor units can be placed on the roof and away from neighbors. In other areas, the outdoor unit must be placed on the ground. In this situation, it must be remembered that a large number of units clustered together can generate noise complaints even if each individual unit has a low sound rating level.

Table 3 illustrates the tolerances allowed for the "A" scale weighting on two instrument types. #2

Residence

35 ft. [10.7 m]

# 3 Open Window

Sound Rating of Unit = 80.0 dB(A) Figure 4. Example of Installation With No Barrier and One Reflective Surface

ARI GUIDELINE L-1997 Table 2. Sample Calculations for Example from ARI Standard 275

As a guide, the following steps have been identified as being necessary for the collection of accurate, on-site sound data:

Evaluation Points Line

Distance from Equipment to Evaluation Point

47 ft. [14.3 m]

15 ft. [4.6 m]

35ft. [10.7 m]

Unit Sound Rating Level

Equipment Location Factor (Table 1, Item 1, ARI 275)

Add Lines 1 and 2

Barrier Shielding Factor (Table 1, Item 2, ARI 275)

Sound Path Factor (Table 1, Item 3, ARI 275)

Distance Factor (Table 2, ARI 275)

Add Lines 4, 5 and 6

Estimated AWeighted Sound Pressure Level (35dB) Subtract Line 7 from Line 3

Table 3. Tolerance, A-Weighted dB Frequency Hz

Type 1

Type 2

63 125 250 500 1000 2000 4000 8000

± 1.0 ± 1.0 ± 1.0 ± 1.0 ± 1.0 ± 1.0 ± 1.0 ± 1.5 - 3.0

± 3.0 ± 2.5 ± 2.5 ± 2.0 ± 2.0 ± 3.0 ± 5.5 - 4.5 ± 6.5

a. Sketch. Make a sketch of the measurement area showing measurement locations, unit orientation and distance to measurement points, lot lines, walls, etc. b. Calibration of Instrumentation. This is done by using an acoustic calibrator, usually a pistonphone, as a source of known sound pressure and adjusting the meter to indicate that level. c. Determination of Background Level. Measure background level without unit operating. This background level must be at least 6 dB below unit operating level or data will be considered invalid due to background contribution. d. Data Collection. Readings should be taken in the slow response mode. When meter fluctuations are less than ±3 dB, an arithmetic mean of maximum and minimum levels can be used. When levels exceed ±3 dB the level may be uncertain and an integrating sound level meter should be used to increase accuracy of data.

ARI GUIDELINE L-1997

APPENDIX A. REFERENCES - NORMATIVE None.

APPENDIX B. REFERENCES - INFORMATIVE B1 Listed here are standards, handbooks, and other publications which may provide useful information and background but are not considered essential. References in this appendix are not considered part of the guideline.

B1.4 ARI Standard 270-95, Sound Rating of Outdoor Unitary Equipment, 1995, Air-Conditioning and Refrigeration Institute, 4301 North Fairfax Drive, Suite 425, Arlington, VA 22203, U.S.A.

B1.1 ANSI Standard S1.4-1983, Specification for Sound Level Meters, 1983, American National Standards Institute, 11 West 42nd Street, New York, NY 10036, U.S.A.

B1.5 ARI Standard 275-97, Application of Sound Rating Levels of Outdoor Unitary Equipment, 1997, Air-Conditioning and Refrigeration Institute, 4301 North Fairfax Drive, Suite 425, Arlington, VA 22203, U.S.A.

B1.2 ANSI Standard S1.11-1986 (R1993), Specifications for Octave-Band and Fractional Octave-Band Analog and Digital Filters, 1993, American National Standards Institute, 11 West 42nd Street, New York, NY 10036, U.S.A.

B1.6 ARI Directory of Certified Unitary Equipment, published semi-annually, Air-Conditioning and Refrigeration Institute, 4301 North Fairfax Drive, Suite 425, Arlington, VA 22203, U.S.A.

B1.3 ANSI Standard S1.42-1986 (R1992), Design Response of Weighting Networks for Acoustical Measurements, 1992, American National Standards Institute, 11 West 42nd Street, New York, NY 10036, U.S.A.

B1.7 ASHRAE Terminology of Heating, Ventilation, Air Conditioning and Refrigeration, American Society of Heating, Refrigerating and AirConditioning Engineers, 1791 Tullie Circle N.E., Atlanta, GA 30329, U.S.A.

ARI GUIDELINE L-1997

APPENDIX C. A-WEIGHTED ADJUSTMENTS AS A FUNCTION OF FREQUENCY A-Weighted Adjustments

Band Center Frequency (Hertz)

One-Third Octave Band Adjustments (dB)

100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000 10000

-19.1 -16.1 -13.4 -10.9 -8.6 -6.6 -4.8 -3.2 -1.9 -0.8 0 +0.6 +1.0 +1.2 +1.3 +1.2 +1.0 +0.5 -0.1 -1.1 -2.5

Octave Band Adjustments (dB) -16.1

-8.6

-3.2

+1.2

+1.0

-1.1