Møller, Henrik

    Aalborg UniversitetChairmans Report on Discussion of ISO/DIS 7196, "Acoustics - Methods for describinginfrasound" at Internoise '84, Honolulu, Hawaii, December 3-5, 1984Møller, HenrikPublished in:Journal of Low Frequency Noise, Vibration and Active ControlPublication date:1984Link to publication from Aalborg UniversityCitation for published version (APA):Møller, H. (1984). Chairmans Report on Discussion of ISO/DIS 7196, "Acoustics - Methods for describinginfrasound" at Internoise '84, Honolulu, Hawaii, December 3-5, 1984. Journal of Low Frequency Noise, Vibrationand Active Control, 4(1), 34-36.General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            ? You may not further distribute the material or use it for any profit-making activity or commercial gain            ? You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us at vbn@aub.aau.dk providing details, and we will remove access tothe work immediately and investigate your claim.Downloaded from vbn.aau.dk on: April 29, 2017Discussion of ISO/DIS 7196 "Acoustics - Methods for Describing Infrasound" at Internoise 84, Honolulu, Hawaii. Report prepared by Henrik Mq,ller. Reprinted from: Journal of Low Frequency Noise & Vibration Vol.4, No.l, 1985 Multi-Science Pub lishing Co Ltd, 42/45 New Broad Street, London EC'.!M lQY. Discussion of ISO/DIS 7196 "Acoustics - Methods for Descnbing Infrasound" at Internoise 84, Honolulu, Hawaii. Report prepared by Henrik M<j>ller. This discussion was suggested by the Chairman of the Internoise 84 Low Frequency Noise Session, Dr. Shinji Yamada, Yamanashi University, Japan. The discussion took place after the Low Frequency Noise Session and was open to all participants in the con-ference. The Chairman of the discussion was Dr. Henrik Mq,ller, Aalborg Univ-ersity, Denmark. Following the Chairman's welcome and introduction, Dr. per V. Bri.ie~ Bri.iel and Kjaer, Denmark, gave a few remarks on the status of the discussion. He stated that, at the time being, the proposal was sent out for discussion through the National Commit-tees and that the official responses would be received this way, too. However, Dr. Briiel found it valuable for the Study Group that handles the proposal (ISO TC 43/ SC 1 Study Group E) to know what the opinion was at this meeting and he would readily report to them in cooperation with the Chairman. (Dr. Bri.iel is a member of the Study Group E). Dr. Brue! gave a short description of the Draft International Standard ISO/DIS 7196. The standard is intended to be used when describing infrasound. It contains two weighting curves that asymptotically follow straight lines from 1 Hz to 20 Hz (Fig. 1). For one curve (named G l) this line has a slope of+ 12 dB per octave and for the other (02) the slope is +6 dB per octave. Both curves have a gain ofO dB at 10 Hz. Outside the frequency range 1-20 Hz the curves are cut off with l pole for frequencies below 1 Hz and 6 poles (G 1) or 5 poles (02) for frequencies above 20 Hz. The Chairman presented six questions which he wanted the audience to discuss and which could structure the debate. The items were: l. Frequency range. 2. Slopes of curves. 3. Rate of cut-off outside the frequency range covered. 4. Reference frequency or gain. 5. Dynamic range of the ear. 6. Averaging time-constant. 1. Frequency range The Chairman raised the question about the frequency range, because a Japanese pro-posal for a weighting curve covers the range 1-50 Hz and because recent research has shown that many problems traditionally attributed to infrasound actually are caused by noise in the low audio range 20-100 Hz. Dr. Briiel agreed that it would be very nice if.frequencies above 20 Hz could be covered, since frequencies from 20 to I 00 Hz are insufficiently covered by the A-curve. However, he found it politically impossible to obtain support for a curve overlapping the A curve. An attempt to extend the frequency range above 20 Hz would probably lead to a rejection of the proposal. Dr. Mq,ller showed that the loudness curves he had measured were parallel, and parallel to the threshold curve, up to 20 Hz. Above this frequency the curves diverge. This means that a single weighting curve cannot be used at all levels if frequencies above 20 Hz are included. So besides the political reasons there are also technical and psy-choacoustical arguments for only including frequencies below 20 Hz. The problems at low audio frequencies must then be solved in another way. Dr. Robert W. Young, San Diego, California, USA, ?.sked, where Dr. Mq,ller's curves were published and whether they were in agreement with possible similar curves measured at other laboratories. Dr. M~ller explained that the curves were published at Intemoise 83 in Edinburgh and that a full paper covering details, such as the method and the standard deviations obtained, would soon appear in the Journal of Low Frequency Noise and Vibration (vol. 3 no. 2, 1984, pp. 78-87). Only one set of curves had previously been published (L.S. Whittle, SJ. Collins and D.W. Robinson: The audibility of low frequency sounds. Journal of Sound and Vibra-tion, vol 21, no. 4, 1972, pp. 431 -448). In that investigation 50 Hz was used as a reference, so the curves did not have a measured connection to 1 kHz. Instead, this con-nection was obtained from the ISO/R 226 curves. At present, there is a discussion of the reliability of the ISO curves at low frequencies and the procedure of Whittle et. al. has led Journal of Low Frequency Noise and 34 Vibration Vo/.4, No.I, 1985 ,, ,, al ,:, w (/) z 0 85 w a: w DISCUSSION OF ISO/DIS 7196 Dr. Brue! proposed an appendix showing equal loudness curves and explaining that a small change in G 1 weighted level will result in a large change in sensation. Dr. Mq,ller suggested a figure showing the approximate connexion between. on the horizontal ax.is the GI weighted sound level and on the vertical axis some kind ofloud-ness or annoyance measure. The loudness or annoyance axis might or might not be calib-rated in, for example, phon or PN dB. Dr. Brtiel expressed his support for this proposal. There was a general agreement that the Standard should contain information about the narrow dynamic range of the ear at these frequencies. 6 poles 10 0,1 02 0,5 2 5 ~o 5CO 1 CCO I 10 0 0 > ' ~ - ,o 10 \. <{ \ \ ...l . I' w I\ a: -20 I \ Zv 12cbl - 30 I ocr -30 I I I 21. db I -40 oct ~o I I , . \G~ I I -50 . GZ\ 50 I I f\ I I -60 I 60 I , _ I l I -70 70 I I -80 eo O,i 02 0,5 2 5 10 20 so 100 200 :ill 1000 F rtquency Ht Figure I Frequency- weighting characteristics of GI - and G 2- weighting 6. Averaging time constant It was suggested that the time constant should be derived from the time constants used with the A curve and the frequency spacing from the A curve to the G2 curve. The low ends of these curves are much alike and spaced about a factor of 25 in frequency (Fig. I.) As the "fast" and "slow" time constants used with the A curve are 125 ms and 1 s, res-pectively, this would give 3.1 sand 25 s to be used with the G2 curve. Dr. Bniel found it sufficient to multiply the time constants by 8, resulting in 1 sand 8 s, which is also close to values used for vibration measurements in this frequency range. Dr. Young raised the question, why two time consta:its were needed. Dr. Brue! and Dr. Mq,ller found it practical to have two: the short one can quickly give a value when mainly frequencies in the range 10-20 Hz are present, while the long one is needed when lower frequencies are involved and very exact values are needed. If somebody tries to use the short time constant when important lower frequencies are involved, the pointer will oscillate and thus warn the operator. The same effect occurs with the A curve, where 125 ms is too short a time constant for measurement of a 20 Hz component. ( Comment: An Annex to the proposed Standard states that a rectangular time window should be used Because of the long settling times that would be required., use of RC type integrators is not recommended. The time window should not be less than 10 s). 36 

Chairmans Report on Discussion of ISO/DIS 7196, "Acoustics - Methods for describing infrasound" at Internoise '84, Honolulu, Hawaii, December 3-5, 1984

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Chairmans Report on Discussion of ISO/DIS 7196, "Acoustics - Methods for describing infrasound" at Internoise '84, Honolulu, Hawaii, December 3-5, 1984

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