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I. PURPOSE <br />CONTENTS <br />PAGE <br />1 <br />II. INTRODUCTION 1 <br />III. PRINCIPLES OF SOUND 1 <br />A. TERMINOLOGY 1 <br />B. ATTENUATION 2 <br />C. HEARING 2 <br />IV. OUTDOOR WARNING SYSTEMS AND DEVICES 3 <br />A. SIRENS 3 <br />B. ELECTRONIC LOUDSPEAKER (OR VOICE /SOUND) SOURCES 3 <br />C. HORNS AND WHISTLES 4 <br />D. RATINGS AND SPECIFICATIONS 4 <br />E. WARNING SIGNALS 4 <br />V. BASIC FACTS ABOUT SOUND OUT OF DOORS 5 <br />A. ATTENUATION WITH DISTANCE 5 <br />1. DIVERGENCE 5 <br />2, ATTENUATION CAUSED BY GROUND EFFECTS 5 <br />3. BARRIERS 6 <br />4. EFFECTS OF VERTICAL TEMPERATURE AND WIND <br />GRADIENTS: ATMOSPHERIC REFRACTION 6 <br />5. FOLIAGE 6 <br />6. ABSORPTION OF SOUND IN THE ATMOSPHERE 7 <br />7. SUMMARY 7 <br />B. HEARING 7 <br />1. LOCAL BARRIERS 7 <br />111 <br />1 1 <br />CPG 1 -17 <br />