ASA-S1.18-1999-R2004.pdf

ANSI S1.18-1999 Reaffirmed by ANSI March 25,2004 American National Standard Template Method for Ground Impedance Secretariat Acoustical Society of America Approved 7 July 1999 American National Standards Institute, Inc. Abstract This American National Standard describes procedures for obtaining the real and imaginary parts of the specific acoustic impedance of natural ground surfaces outdoors. The Standard uses templates to compare measured sound pressure level differences with a specific set of calculated level differences. The impedance values are obtained from a model based on best fit of measured and calculated level differences. The Standard may also be used to obtain the impedance of porous sound absorbing material. Copyright Acoustical Society of America Provided by IHS under license with ASA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/18/2007 05:29:07 MDTNo reproduction or networking permitted without license from IHS -,-,- AMERICAN NATIONAL STANDARDS ON ACOUSTICS The Acoustical Society of America (ASA) provides the Secretariat for Accredited Standards Committees S1 on Acoustics, S2 on Mechanical Vibration and Shock, S3 on Bioacoustics, and S12 on Noise. These committees have wide represen- tation from the technical community (manufacturers, consumers, and general- interest representatives). The standards are published by the Acoustical Society of America through the American Institute of Physics as American National Stan- dards after approval by their respective standards committees and the American National Standards Institute. These standards are developed and published as a public service to provide standards useful to the public, industry, and consumers, and to Federal, State, and local governments. Each of the Accredited Standards Committees (operating in accordance with pro- cedures approved by ANSI) is responsible for developing, voting upon, and main- taining or revising its own standards. The ASA Standards Secretariat administers committee organization and activity, and provides liaison between the Accredited Standards Committees and ANSI. After the Standards have been produced and adopted by the Accredited Standards Committees, and approved as American National Standards by ANSI, the ASA Standards Secretariat arranges for their publication and distribution. An American National Standard implies a consensus of those substantially con- cerned with its scope and provisions. Consensus is established when, in the judgment of the ANSI Board of Standards Review, substantial agreement has been reached by directly and materially affected interests. Substantial agreement means much more than a simple majority, but not necessarily unanimity. Consen- sus requires that all views and objections be considered and that a concerted effort be made toward their resolution. The use of American National Standards is completely voluntary. Their existence does not in any respect preclude anyone, whether he or she has approved the standards or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not conforming to the standards. NOTICE: This American National Standard may be revised or withdrawn at any time. The procedures of the American National Standards Institute require that action be taken periodically to reaffirm, revise, or withdraw this Standard. Standards Secretariat Acoustical Society of America 120 Wall Street, 32nd Floor New York, New York 10005-3993 USA Telephone: +I 212 248 0373 Telefax: +1 212 248 0146 E-mail: asastds Qaip.org Internet: http:/asa.aip.org Oí999 by the Acoustical Society of America. This Standard may not be reproduced in whole or in pari in any form for sale, promotion, or any cornmerciai purpose, or any purpose not falling within the provisions of the Copyright Act of 1976, without prior written permission of the publisher. For permission, address a written request to the Standards Secretariat of the Acoustical Society of America. Copyright Acoustical Society of America Provided by IHS under license with ASA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/18/2007 05:29:07 MDTNo reproduction or networking permitted without license from IHS -,-,- Contents Page Foreword . 111 Introduction 1 O Scope . 1 1 2 Purpose 1 3 Application 4 References to other standards . 2 6 Tutorial 2 6.1 General . 2 6.2 Geometrical divergence . 2 6.3 Air absorption 2 6.4 Effects of the environment . 3 7 Measurement method . 3 7.1 Recommended geometries 3 7.2 Measurement procedure 3 of the ground impedance 7.3.1 One-parameter model . 4 7.3.2 Two-parameter model . 4 7.3.3 User-defined model . 5 7.4 Procedure to determine best fit 5 8 Instruments for measuring ground impedance outdoors . 5 8.1 Sound source 5 8.2 Microphone 5 8.3 Calibration . 6 8.4 Sound level meter/analyzer 6 8.5 Miscellaneous 6 8.6 Configuration of measuring system . 6 8.7 Wind speed 6 9 Measurement 6 9.1 Area of ground . 6 9.2 Data collection . 6 9.2.1 Initial and final calibration . 6 9.2.2 Meteorological . 6 9.2.3 Signal to noise . 6 10 Data reduction . 6 10.1 Corrections 6 10.1.1 Correction for frequency response of measurement system . 6 . . 1 5 Definitions . 2 7.3 Determination of real and imaginary parts 4 10.1.2 Correction for excessive background sound . 7 10.2 Experimental error 7 11 Reporting 7 11.1 Introductory information . 7 11.2 Documentation of the instrumentation . 7 11.3 Meteorological data . 8 11.4 Impedance data 8 I Copyright Acoustical Society of America Provided by IHS under license with ASA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/18/2007 05:29:07 MDTNo reproduction or networking permitted without license from IHS -,-,- Page 1 1.5 8 12 References 8 Other observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . Templates 1A 1B 1C 2A 28 2C Pre-calculated level differences (dB) for Geometry A using the one-parameter model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pre-calculated level differences (dB) for Geometry B using the one-parameter model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pre-calculated level differences (dB) for Geometry C using the one-parameter model . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . Pre-calculated level differences (dB) for Geometry A using the two-parameter model . . . . . . . . . . . . . . . . . . . . . . , . . , . . . . Pre-calculated level differences (dB) for Geometry B using the two-parameter model . . . . . . . . . , . . . . . . . . . . . . . . . . . , . . Pre-calculated level differences (dB) for Geometry C using the two-parameter model . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . 9 10 11 12 15 18 Annexes A A.l B B.l 6.2 8.2.1 8.2.2 B.2.3 Institutional grass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sample results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . User-defined templates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calculated level differences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Published data for ground surfaces and user-defined models . . . . One-parameter model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Two-parameter model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Four-parameter model and its simplifications . . . . . . . . . . . . . . . . . . 21 21 23 23 23 23 23 23 Tables 1 A.l B.l 8.2 Adjustment of measured level to account for the effect Level difference measurements above institutional grass . . . . . . . . 22 Flow resistivity data for ground surfaces . . . . . . . . . . . . . . . . . . . . . . 24 Ground classification and indicative best-fit two-parameter model values 24 of background sound . 7 Figures 1 Geometrical definitions: /?,=source height, h,= top microphone height, h,=bottom microphone height, d=source/receiver horizontal separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Level difference measurements above grass plotted on Template 1A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . Level difference measurements above grass plotted on Template 2A (ae=3 m-) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 21 22 A.l A.2 II Copyright Acoustical Society of America Provided by IHS under license with ASA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/18/2007 05:29:07 MDTNo reproduction or networking permitted without license from IHS -,-,- Foreword This Foreword is for information only and is not a pad of American National Standard Template Method for Ground Impedance, ANSI S 1 .18- 1 999.1 This Standard was developed under the jurisdiction of Accredited Standards Com- mittee S1, Acoustics, using the American National Standards Institute (ANSI) Ac- credited Standards Cornmittee Procedure. The Acoustical Society of America pro- vides the Secretariat for Accredited Standards Committee S1, Acoustics. Accredited Standards Committee S1, Acoustics, under whose jurisdiction this Standard was developed, had the following scope: Standards, specifications, methods of measurement and test, and terminology in the fields of physical acoustics including architectural acoustics, electro- acoustics, sonics and ultrasonics, and underwater sound, but excluding those aspects which pertain to biological safety, tolerance, and comfort. At the time this Standard was submitted to Accredited Standards Committee S1, Acoustics, for approval, the membership was as follows: J. P. Seiler, Chairman G. S. K. Wong, Vice Chair A. Brenig, Secretary Acoustical Society of America J. P. Seiler G. S. K. Wong (Alt.) Air-Conditioning and Refrigeration Institute R. Comparin S. Sanders (Alt.) American Industrial Hygiene Association L. H. Royster J. F. Meagher (Alt.) Audio Engineering Society L. W. Sepmeyer M. R. Chial (Alt.) Bruel for this case the atmosphere can be regarded as ho- mogeneous and the ray paths approximated by straight lines. The attenuation due to the effects of the environment (Aenv) is then that due to the ground alone. For greater distances, meteorological conditions usually become a major factor. These factors are refraction by wind, temperature gradients, and at- mospheric turbulence. The meteorological effects modify the ground attenuation to produce the total attenuation due to the environment. When the sound source is located above a ground surface, sound waves that reflect from the ground will constructively or destructively interfere with those propagating directly from the source. Since most grounds are partially reflecting, the reflected wave is also modified in amplitude and phase by its interaction with the ground surface. The amount of attenuation attributable to this ground interac- tion and its variation with frequency depends on the surface type and the sourceíreceiver heights and their separation. The effects of the ground are largest for intermediate frequencies (around 500 Hz) when the source is above the ground (1 m or more). If the source is close to the ground all fre- quencies above 500 Hz display large attenuations. This Standard uses short propagation distances (less than 2 m) to ensure that A , , is due to the ground alone. The Standard uses the variation of the ground attenuation with ground properties to obtain the impedance. 7 Measurement method 7.1 Recommended geometries Level differences from two collated microphones are obtained as a function of frequency. The mea- surement shall be made using a point source as defined in clause 8.1, two identical microphones, and one or more of the following geometries (see figure 1): Geometry A Source height=32.5 cm Top microphone height=46.0 cm Bottom microphone height=23.0 cm Source/receiver horizontal separation= 1.75 m Figure 1 - Geometrical definitions: he= source height, h,=top microphone height, hb = bottom microphone height, d=source/rece¡ver horizontal separation. Geometw B Source height=20.0 cm Top microphone height=20.0 cm Bottom microphone height=5.0 cm Source/receiver horizontal separation= 1 .O m Geometry C Source height=40.0 cm Top microphone height=40.0 cm Bottom microphone height=5.0 cm Source/receiver horizontal separation = 1 .O m Geometry A covers the broadest range of frequen- cies. Geometry B emphasizes ground effect at fre- quencies above 1000 Hz and may be better suited for hard grounds. Geometry C emphasizes ground effect at frequencies below 1000 Hz and may be better suited for very soft grounds. 7.2 Measurement procedure The test signal shall consist of single pure tones spaced at least at one-third-octave band center frequencies, broadband random noise, pseudo- random noise, sine-sweep excitation, or other similar test signals. Single pure tones may be the desired test signals in the presence of excessive background sound. One of the other test signals may be desirable for more rapid measurements. The frequency ranges below 250 and above 4000 Hz are not covered by this Standard. The sound source shall generate a sound level at each microphone location that is at least 10 dB greater than ambient noise (source off) at the fre- quency or frequencies of interest. Test data for CI 1999 Acoustical Society of America 3 Copyright Acoustical Society of America Provided by IHS under license with ASA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/18/2007 05:29:07 MDTNo reproduction or networking permitted without license from IHS -,-,- ANSI S1.18-1999 which this criterion is not met should be identified accordingly and may be corrected as described in clause 1 O. 1.2. It should be anticipated that the ground impedance will vary with location. Consequently, a sufficient number of measurements should be taken to es- tablish the variability with position. For each geom- etry, a minimum of four independent measure- ments shall be made. The source and microphone shall be translated and/or rotated to an adjacent piece of identical ground. A minimum of six fre- quencies shall be used. For each measurement and each frequency or fre- quency band, the level difference between the top and bottom microphones shall be calculated. Then the average value and the standard deviation of the level difference in each set of n independent measurements shall be calculated. No measurement shall be made when the average wind velocity exceeds 5 m/s when measured at a height of 2.0 m above the ground. No measurements shall be made during precipita- tion. The ground shall be in the condition desired for the measurements. It can be d