STD.150 266-EN6L 1997 4851903 0703698 367 INTERNATIONAL ISO STANDARD 266 Second edition 1997-04-01 Acoustics Preferred frequencies AcoustiqueFrequences normales This material is reproduced from Iso documents under International Organization for Standardization (IsO) Copyright License number 1HS/IcC/1996. Not for resale. No part of these Iso documents may be reproduced in any form, electronic retrieval system or otherwise, except as consent of Iso (Case postale 56, 1211 Geneva 20, Switzerland, Fax +41 22 734 10 79), IHS or the IS0 Licensor's members. so Reference number 1SO 266:1997(E) Copyright International Organization for Standardization Not for Resale STD.ISO 266-ENGL 1997 E06t59h E12 669E020 8 ISO 266:1997(E) Foreword IsO (the international Organization for Standardization) is a woridwide federation of national standards bodies (isO member bodies). The work of preparing Internationai Standards is normally carried out through IsO technicai committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non- governmental, in liaison with IsO, also take part in the work. ISo collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IsO 266 was prepared by Technica! Committee ISO/TC 43,Acoustics. This second edition cancels and replaces the first edition (IsO 266:1975), which has been technically revised. Annex A of this International Standard is for information only. @ISO1997 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Casepostale56CH-1211Geneve20Switzerland Internet [email protected] X.400 C=ch; a=400net; p=iso; 0=isocs; s=central Printed in Switzertand ii Copyright International Organization for Standardizatior Not for Resale STD.IS0 26b-ENGL 199? 48519030703700845 @ISO ISO 266:1997(E) Introduction This International Standard specifies a series of preferred frequencies in order to provide a common basis for comparing the results of acoustical measurements. The frequency series is referred to the reference frequency of 1 000 Hz, which is also the reference frequency for the definition of the phon (see isO 31-7). The specification of the preferred frequency series reduces to a minimum the number of frequencies at which acoustical data need to be tabulated. Also measurement equipment may be specifically constructed for these frequencies. The specified series of preferred frequencies uses powers of 10 and is therefore especially convenient for extensions into the infrasonic and ultrasonic (frequency) ranges. Another series of frequencies that is in use is based on the definition of the octave as the frequency ratio 1:2. The frequencies of this series are calculated as powers of two (IEC 1260 base two series). Strictly, these two series are incompatible. However the base-two series because of the fact that 21/3 _ 1,259 9... is very nearly the same as 101/10=1,2589... Practical considerations make some additional rounding desirable: Thus 500 Hz is listed instead of 501,187 233... Hz, which is the exact frequency from the base-ten series. The calculated value of the exact frequency expressed to five significant figures is given in the second column of table 1. In this way, the maximum individua! deviation, in the frequency range 20 Hz to 20 000 Hz, between the rounded preferred frequencies and the calculated frequencies for the