SOUND MASKING DONE RIGHT: SIMPLE SOLUTIONS FOR COMPLEX PROBLEMS Robert Chanaud, Ph.D. Magnum Publishing L.L.C. i Copyright 2008, Robert Chanaud, All Rights Reserved Published with permission by Magnum Publishing, LLC No part of this book may be reproduced, stored in a retrieval system, or transmitted in any other form, or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission of the publishers. While every effort has been made to ensure that the contents of this document are accurate and reliable, Magnum Publishing LLC, Robert Chanaud, or Atlas Sound L.P. cannot assume liability for any damages caused by inaccuracies in the data or documentation, or as a result of the failure of the data, documentation, software, or products described herein to function in a particular manner. The authors and publishers make no warranty, expressed or implied, nor does the fact of distribution constitute a warranty. International Standard Book Number: 978-0-9818166-0-9 Printed in the United States of America ii - Sound Masking Done Right: Simple Solutions for Complex Problems - About Bob Chanaud Dr. Robert C. Chanaud received his BS from the US Coast Guard Academy, his MS from the University of California and his PhD from Purdue University. Active in the field of acoustics since 1958, he taught at Purdue University and the University of Colorado and, in 1975, founded Dynasound, Inc. He has developed software programs to facilitate the design and equalization of masking systems. Acknowledgements The following companies have graciously supplied products for evaluation: Atlas Sound Cambridge Sound Management Dynasound Soft dB Sound Advance Notation Square brackets [ ] are references contained at the end of the manual. Parentheses ( ) refer to other sections in the manual. - Robert Chanaud, Ph.D. - iii PREFACE This manual attempts to cover enough material on acoustical privacy in rooms to help the designer to appreciate the value of sound masking as a key privacy tool. Over the last thirty years there have been innumerable articles on privacy and how to achieve it, in both professional journals and trade literature. In particular, the reader is referred to the large number of comprehensive documents published by the National Research Council, Canada. Unfortunately, they refer to that restful sound masking as “noise”. Sound masking is still steeped in mythology. The important difference between quiet and privacy is still unclear to most. Architects are trained primarily in the visual arts, so structural factors, such as walls, are the key privacy elements for them. Although privacy caused by background sound is an everyday event for all of us, the idea of controlling it deliberately still meets resistance. The social context is one reason. I am always amazed to find someone who thinks masking in the workplace is too loud at 45 dBA, but is not bothered by the 78 dBA found in the cabin of a commercial aircraft. Another reason is the contractor that installs a sound masking system that creates nothing but noise from the ceiling, resulting in the justified comment that “masking doesn’t work”. One purpose of the manual is to give the potential user and the contractor enough information to prevent these disasters. This manual focuses on “open” systems. For open systems, the end user is free to choose from among several contractors and the contractor is free to choose products from among several manufacturers based on their performance and price. For proprietary systems, the end user may be restricted to one manufacturer who may have only one authorized distributor locally. iv - Sound Masking Done Right: Simple Solutions for Complex Problems - TABLE OF CONTENTS Chapter 1 - Criteria for the Design of Sound Masking Systems 1.1 What is Masking and what does it do? ...................................1 1.2 What’s in a Name? ....................................................1 1.3 The Fallacious Quest for Quiet ..........................................2 1.4 The Evolution of Sound Masking ........................................3 1.5 The Major Reason for Developing Sound Masking .........................3 1.6 The Reputation of Sound Masking .......................................4 1.7 Sound Masking vs. Noise Cancellation ...................................4 1.8 Two Characteristics of Office Noise ......................................5 1.8.1 Transient Sounds .............................................5 1.8.2 Steady Sounds ...............................................5 1.9 The Needs of Employees in an Office ....................................6 1.9.1 Communication ...............................................6 1.9.2 Privacy ......................................................6 1.9.3 Community ..................................................6 1.10 The General Effects of Noise on People .................................6 1.10.1 Physical ....................................................7 1.10.2 Physiological ................................................7 1.10.3 Psychological ...............................................7 1.11 Specific Studies of Noise in the Office Environment .......................7 1.12 Common Opinions about Sound .......................................8 1.12.1 Is the sound made by me or made on my behalf? .................8 1.12.2 Is the sound “normal” for this environment? .....................8 1.12.3 Is the sound necessary and can anything he done to control it? ........8 1.12.4 Does the sound have meaning? ...................................8 1.12.5 Is the sound frightening? ........................................9 1.12.6 Will the sound have an adverse effect on my health? ................9 1.12.7 What is the pitch of the sound? ....................................9 1.12.8 How reverberant is the room? ....................................9 1.13 Noise Complaints in the Office .........................................9 1.14 Applications of Sound Masking ........................................10 1.15 Advantages of Sound Masking ........................................11 1.16 Potential Disadvantages of Sound Masking ..............................11 Chapter 2 - Speech Privacy 2.1 Types of Speech Privacy ...............................................13 2.2 Degrees of Privacy ....................................................13 2.2.1 Secret Privacy ................................................14 2.2.2 Confidential Privacy ...........................................14 2.2.3 Normal Privacy ...............................................14 2.2.4 Transitional Privacy. 14 2.2.5 No Privacy ...................................................15 2.3 Factors Determining Speech Privacy .....................................16 2.4 Standards for Determining Speech Privacy ...............................17 2.4.1 PBS/GSA ....................................................17 2.4.2 ANSI .......................................................17 2.4.3 ASTM .......................................................17 2.5 Privacy Index and Speech Privacy .......................................18 2.6 Determining the Value of Sound Masking .................................19 2.7 Variability of Privacy Needs ............................................20 - Robert Chanaud, Ph.D. - v Chapter 3 - Achieving Acoustical Privacy 3.1 Privacy In Open Rooms ................................................21 3.1.1 Factors that Reduce Speech Transmitted to Listeners ...............21 3.1.2 Sound Sources and Paths ......................................23 3.1.3 Structural Elements ...........................................24 3.1.4 ......................................... Combining the Factors 27 3.1.5 Creating Privacy with Sound Masking ............................29 3.1.6 The Masking Spectrum Dilemma ................................30 3.1.7 Universal Privacy with Sound Masking ...........................32 3.1.8 The Total Masking Spectrum ....................................35 3.1.9 Partial Privacy with Sound Masking ..............................35 3.1.10 Making Sound Masking Work ..................................36 3.1.11 Other Applications ...........................................37 3.1.12 Handling the Spatial Aspects of Privacy ..........................38 3.1.13 Handling the Temporal Aspects of Privacy ........................39 3.2 Privacy in Closed Rooms ..............................................42 3.2.1 The Problem .................................................42 3.2.2 The Construction Solution ......................................42 3.2.3 Speech Weighted Ratings ......................................45 3.2.4 Making Sound Masking Work ...................................46 3.2.5 Other Applications ............................................46 3.3 Modeling Speech Privacy ..............................................48 3.3.1 Storing Physical Attributes of the Space ..........................50 3.3.2 Storing Representative Masking Spectra ..........................50 3.3.3 Modeling the Space ...........................................51 3.3.4 Modeling the Sound Attenuation ................................52 3.3.5 Modeling the Sound Masking ...................................53 3.3.6 Additional Results for Open Offices ..............................55 3.3.7 Calculating Speech Privacy from Measured Sound Attenuation .......57 Chapter 4 - Privacy in Medical Facilities 4.1 Federal Regulations ...................................................59 4.2 The Noise Problem ...................................................60