1、 2013 Standard for Performance and Calibration of Reference Sound Sources AHRI Standard 250-2013 Price $10.00 (M) $20.00 (NM) Copyright 2013, by Air-Conditioning, Heating, and Refrigeration Institute Printed in U.S.A. Registered United States Patent and Trademark Office IMPORTANT SAFETY DISCLAIMER A
2、HRI does not set safety standards and does not certify or guarantee the safety of any products, components or systems designed, tested, rated, installed or operated in accordance with this standard/guideline. It is strongly recommended that products be designed, constructed, assembled, installed and
3、 operated in accordance with nationally recognized safety standards and code requirements appropriate for products covered by this standard/guideline. AHRI uses its best efforts to develop standards/guidelines employing state-of-the-art and accepted industry practices. AHRI does not certify or guara
4、ntee that any tests conducted under its standards/guidelines will be non-hazardous or free from risk. This standard supersedes ANSI/AHRI Standard 250-2008. This standard differs from the 2008 version in that it references ISO 6926 for atmospheric and barometric corrections and ANSI Standard S12.55 f
5、or room qualification methods. TABLE OF CONTENTS SECTION PAGE Section 1. Purpose .1 Section 2. Scope 1 Section 3. Definitions 1 Section 4. Performance Requirements 2 Section 5. Primary RSS Calibration Procedure .3 Section 6. Secondary RSS Transfer Calibration Procedure 4 Section 7. Test Requirements
6、 5 Section 8. Test Data To Be Recorded .5 Section 9. Information To Be Recorded 6 Section 10. Minimum Data Requirements for Published Information 6 Section 11. Frequency of Calibration. .6 Section 12. Conformance Conditions 7 TABLES Table 1. RSS Sound Power Level Output Standard Deviations .2 Table
7、2. Minimum Reverberation Room Volume for Secondary RSS Transfer Calibration 4 Table 3. RSS Tolerance Levels 7 FIGURES Figure 1. Microphone Path 3 APPENDICES Appendix A. References Normative .8 Appendix B. References Informative .8 Appendix C. Alternative Primary RSS Calibration Procedure Normative .
8、9 Appendix D. Procedures for Determining Windscreen Corrections Normative .10 Appendix E. Example for the Determination of the Directivity Index and Resultant RSS Calibration Informative .11 TABLES FOR APPENDICES Table C1. Tolerance for Sound Power Level Difference 9 Table E1. Example for the Determ
9、ination of the Directivity Index and Resultant RSS Calibration 11 Table E2. RSS Maximum Sound Pressure Levels in One-third Octave Bands, Lpi.12 Table E3. RSS One-third Octave Bands Directivity Index, dB 13 Table E4 Resultant RSS Calibration 13 AHRI STANDARD 250-2013 1 PERFORMANCE AND CALIBRATION OF
10、REFERENCE SOUND SOURCES Section 1. Purpose 1.1 Purpose. The purpose of this standard is to establish the performance characteristics of a Reference Sound Source, define the acoustical calibration procedures, and define the method for transfer of calibration from a Primary to a Secondary Reference So
11、und Source. 1.1.1 Intent. This standard is intended for the guidance of the industry, including manufacturers, engineers, installers, contractors and users. 1.1.2 Review and Amendment. This standard is subject to review and amendment as technology advances. Section 2. Scope 2.1 Scope. This standard
12、applies to all Reference Sound Sources used in conjunction with AHRI sound rating standards and covers the one-third octave band frequency range from 50 to 10,000 Hz. This standard also includes calibration over a limited frequency range. Multiple Reference Sound Sources may be used to cover the ent
13、ire frequency range from 50 to 10,000 Hz. Section 3. Definitions All terms in this document will follow standard industry definitions in the ASHRAE Wikipedia website (http:/wiki.ashrae.org/index.php/ASHRAEwiki) unless otherwise defined in this section. 3.1 Directivity Index (Di). An indicator, expre
14、ssed in decibels (dB), of the non-uniform spatial sound radiation of the Reference Sound Source being calibrated. 3.2 Hertz (Hz). A unit of frequency equal to one cycle per second. 3.3 Octave Band. A band of sound covering a range of frequencies such that the highest is twice the lowest. The Octave
15、Bands used in this standard are those defined in ANSI Standard S1.11. 3.4 One-third Octave Band. A band of sound covering a range of frequencies such that the highest frequency is the cube root of two times the lowest frequency. The One-third Octave Bands used in this standard are those defined in A
16、NSI Standard S1.11. 3.5 Reference Sound Source (RSS). A portable, aerodynamic sound source that produces a known stable broad band sound power output. The device shall meet the performance requirements as defined in Section 4. 3.5.1 Primary Reference Sound Source. A laboratory RSS whose Sound Power
17、Levels are determined by using the procedures as defined in Section 5. 3.5.2 Secondary Reference Sound Source. A laboratory RSS whose Sound Power Levels are determined by using the transfer calibration procedure as defined in Section 6. 3.6 Sound Intensity Level, Li. Ten times the logarithm to the b
18、ase ten of the ratio of the magnitude of the intensity to the reference intensity of 1 picowatt per square meter (pW/m2). 3.7 Sound Power Level, Lw. Ten times the logarithm to the base ten of the ratio of the sound power radiated by the source to a reference sound power, expressed in decibels (dB).
19、The reference sound power used in this standard is 1 picowatt (pW). AHRI STANDARD 250-2013 2 3.8 Sound Pressure Level, Lp. Twenty times the logarithm to the base ten of the ratio of a given sound pressure to a reference sound pressure of 20 Pa, expressed in decibels (dB). 3.9 “Shall” or “Should”. “S
20、hall” or “should” shall be interpreted as follows: 3.9.1 Shall. Where “shall” or “shall not” is used for a provision specified, that provision is mandatory if compliance with the standard is claimed. 3.9.2 Should. “Should” is used to indicate provisions which are not mandatory but which are desirabl
21、e as good practice. Section 4. Performance Requirements 4.1 Type of Sound Source. A portable, aerodynamic sound source that produces a known stable broad band sound power output. The sound source shall have no pure tones within the frequency range of interest. The presence of a tone is indicated by
22、variation in adjacent One-third Octave Bands of more than 3 decibels. 4.2 Reference Sound Source Spectral Characteristics. The spectrum of the Reference Sound Source shall be broad band and the spread of one-third octave band Sound Power Levels of the RSS when calibrated over the frequency range of
23、50 10,000 Hz shall not exceed 16 dB. When the Reference Sound Source is only calibrated over the frequency range of 100 to 10,000 Hz the spread of one-third octave band Sound Power Levels of the RSS shall not exceed 12 dB. Regardless of the frequency range of calibration adjacent bands shall not dev
24、iate by more than 3 dB to avoid the presence of tones when tested in accordance with this standard. 4.3 Reference Sound Source Size. The largest dimension of the source shall not exceed 0.5 m. 4.4 Vibration Isolation. The RSS shall be equipped with integral vibration isolation so that it will provid
25、e a minimum of 95% isolation at its rotational speed. 4.5 Temporal Steadiness and Repeatability of the Sound Power Output. The Reference Sound Source shall be designed and constructed so that the Sound Power Level in each One-third Octave Band is constant in time within the limits defined in Table 1
26、 for the required measurement period. The values in Table 1 represent the expected repeatability of the measurements. Temperature and barometric pressure corrections shall be performed per Clause 8.4 of ISO 6926. Table 1. RSS Sound Power Level Output Standard Deviations Frequency Range, Hz Sound Pow
27、er Level Output Standard Deviation, dB 50 - 80 0.8 100 - 160 0.4 200 10,000 0.2 4.5.1 Sound Power Level Variation from Electrical Variation. The RSS Sound Power Level in any One-third Octave Band shall not vary by more than 0.3 dB within the range of the source electrical power. The manufacturer of
28、the RSS shall provide the tolerances of electrical input power to assure no more than a 0.3 dB deviation. 4.5.2 Sound Power Level Variation from Atmospheric Conditions. The Sound Power Level of the Reference Sound Source may depend on the atmospheric pressure and temperatures along with the altitude
29、. The manufacturer of the RSS shall provide correction values for these variables. 4.6 Directivity Index. The Directivity Index of the Reference Sound Source in any One-third Octave Band from 50 to 10,000 Hz at any microphone height shall not exceed + 6 dB. See Section 5.8 for procedure to determine
30、 Directivity Index. AHRI STANDARD 250-2013 3 Section 5. Primary Reference Sound Source Calibration Procedure 5.1 General. The RSS calibration procedure shall be carried out in accordance with the provisions of Section 5 for sound pressure measurements in a hemi-anechoic room or as provided in Append
31、ix C for using the sound intensity method. Calibration of the laboratory instrumentation system used for this procedure shall be verified at intervals in a calibration laboratory demonstrating traceability to appropriate standards. 5.2 Test Environment. The test environment shall be a hemi-anechoic
32、space meeting or exceeding the qualification requirements of ANSI Standard S12.55. The hard surface shall extend at least 1 m beyond the projection of the measurement surface in all directions. In addition, the volume of the test room shall be greater than 280 m3. 5.3 Microphone. A calibrated 12 mm
33、free field microphone mounted with its axis 0otowards the Reference Sound Source shall be used. The microphone frequency response shall be corrected to give a flat frequency response within 0.1 dB over the frequency range of interest. 5.4 Microphone Positions. The measurement surface shall be a hemi
34、sphere with a radius of 2 m. The center of this hemisphere shall be located on the floor directly below the center of the RSS fan wheel. 5.5 Microphone Path. The path to be used is defined as twenty coaxial, horizontal circular traverses on the surface of the 2 m radius hemisphere and around a verti
35、cal axis passing through the center of the RSS fan wheel. The traverse speed shall not exceed 1 rpm. The twenty coaxial, horizontal circular traverses shall start at a height of 0.025r (r = radius) starting from the floor and increase in 0.05r increments to 0.975r in Figure 1. Figure 1. Microphone P
36、ath The circular path may be achieved by uniformly rotating either the microphone or RSS through 360. If the RSS is to be rotated, the top surface of the turntable shall be flush with the floor (rotational speed not to exceed 1 rpm). 5.6 Measurements. Measure the one-third octave band Sound Pressure
37、 Level in accordance with ANSI Standard S12.55 with an integration time equal to one complete revolution of the microphones or source. The analyzer shall be capable of making measurements to 0.1 dB. 5.7 Calculations. The one-third octave band Sound Power Levels shall be computed per ANSI Standard S1
38、2.55 using the surface Sound Pressure Levels calculated in accordance with ANSI Standard S12.55 and they shall be rounded to the nearest 0.1 decibels. Reflecting PlaneHeight above reflecting plane (m)1.951.851.751.651.551.451.351.251.151.050.950.850.750.650.550.450.350.250.150.05RSSAxis of rotation
39、for microphone traverseHeight for each of 20 microphone slices2 m radius hemisphereAHRI STANDARD 250-2013 4 5.8 Directivity Index Calculation. The maximum measured Sound Pressure Level or maximum measured Sound Intensity Level for each One-third Octave Band at each microphone height shall be used to
40、 compute the Directivity Index. The Directivity Index shall not be computed for the 0.025r microphone height. The maximum calculated Directivity Index for each One-third Octave Band shall be published per Section 10.2 item l and calculated per Equation 1. Di= Lpior Lii Lp1 Where: Di= Directivity Ind
41、ex for a given One-third Octave Band Lpi= Maximum measured Sound Pressure Level for a given One-third Octave Band at a given microphone height or Lii= Maximum measured Sound Intensity Level for a given One-third Octave Band at a given microphone height Lp= Average Sound Pressure Level for a given On
42、e-third Octave Band over the surface of the measurement hemisphere Refer to Appendix E for an example. 5.9 Instrumentation and Equipment. The instrumentation and equipment shall meet or exceed the requirements of ANSI Standard S12.55. 5.10 Use of Windscreens. If a windscreen is used it shall not aff
43、ect the microphone response by more than 1 dB from 50 to 4,000 Hz or 1.5 dB for frequencies above 4,000 Hz. Windscreen corrections shall be determined per Appendix D of this standard. These corrections shall be added to the measurements made in Section 5.6 or Appendix C of this standard. 5.11 Calibr
44、ation Over a Limited Range. This standard allows the RSS to be calibrated over a limited range of frequencies. If the RSS is calibrated over a limited range then the range of calibration shall be reported. Note: A limited range may not be acceptable for all AHRI standards. Section 6. Secondary Refer
45、ence Sound Source Transfer Calibration Procedure 6.1 Test Environment. The test environment shall be a reverberation room meeting or exceeding the qualification requirements of ANSI/AHRI Standard 220 over the frequency range of interest. 6.2 Reverberation Room Volumes. Minimum reverberation room vol
46、umes shall be as listed in Table 2. Table 2. Minimum Reverberation Room Volume for Secondary RSS Transfer Calibration Lowest One-third Octave Band of Interest, Hz Minimum Reverberation Room Volume, m350 280 100 200 200 70 6.3 Microphone(s) Location. Microphone(s) location shall be as per specified i
47、n ANSI/AHRI Standard 220. 6.4 RSS Locations. The Reference Sound Sources shall be placed in a minimum of four locations within the reverberation room for testing. The locations and the orientations shall be the same for each source and these locations shall be positions that were used in qualifying
48、the reverberation room per ANSI/AHRI Standard 220. AHRI STANDARD 250-2013 5 6.5 Measurements. The one-third octave band Sound Pressure Levels shall be measured in accordance with ANSI/AHRI Standard 220 for the RSS. The analyzer integration time shall be the same for all measurements and a minimum of
49、 64 seconds. When using a traversing microphone, the analyzer integration time shall be equal to a whole number of microphone traverses. The analyzer used shall have a measurement resolution of at least 0.1 dB. 6.6 Calculations. One-third octave band Sound Power Levels for the RSS shall be calculated by using the average of the measured Sound Pressure Levels (rounded to the nearest 0.1 decibel) of the RSS. The RSS Sound Power Levels, LwSEC, shall be computed and reported to the nearest 0.1 decibel, as follows for each One-third Octave Band of interest in Equation
