ISO INTERNATIONAL STANDARD 11820 First edition 1996-12-15 Acoustics -- Measurements on silencers in situ AcoustiqueMesurages sur silencieux in situ This material is reproduced from Iso documents under International Organization for Standardization (Iso) Copyright License number IHS/ICC/1996. Not for resale, No part of these IsO documents may be reproduced in any form, electronic retrieval system or otherwise, except as allowed in the copyright law of the country of use, or with the prior written consent of Iso (Case postale 56, 1211 Geneva 20, Switzerland, Fax +41227341079),iHSor theISo Licensor'smembers. ISO Reference number ISO 11820:1996(E) No reproduction or networking permited without license from IHS Not for Resale ISO 11820:1996(E) Contents Page 1 Scope 1 2 Normative references .. 2 3 Definitions. 2 4 Correctionsforbackgroundnoise.. 4 4.1Transmission sound pressure level difference 4 4.2 Insertion sound pressure level difference.. 5 Installation conditions . 5 5 6 Measuring instruments . 5 6.1 Acoustic instruments 5 6.2 Air flow, static pressure and temperature measuring devices.. 7 Test object and measuring conditions .. 7 8 Measurement procedures.. 7 8.1 General.. 7 8.2 Acoustic measurements 7 8.3Flow, pressure and temperature measurements.... 9 Evaluation 10 9.1 Evaluationofsoundpressuremeasurements.. 10 9.2 Evaluation of flow measurements. 12 10 Information to be recorded 13 11 Information to be reported 14 Annexes A Field corrections . 15 B Calibration of directional microphones and microphones equipped with a turbulence windscreen .... 17 Bibliography 18 c ISO1996 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 OrganizationforStandardization Case Postale 56. CH-1211 Geneve 20 . Switzerland Printed in Switzertand Copyright Intemational Organization for Standardization No reprodu rom IHS Not for Resale @ISO ISO11820:1996(E) Foreword ISO(theInternationalOrganizationforStandardization)isaworldwidefed- eration of national standards bodies (isO member bodies). The work of technical 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 dnon- governmental, in liaison with ISO, aiso take part in the work. ISO collab- orates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted bythe technical committees are cir- culated 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 11820 was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise. Annexes A to C of this International Standard are for information only ili Copyihtlntemational Organizain or tandardization No reproduction or networking permitted without license from IHS Not for Resale