User Guide

Sound System Design Reference Manual
Table of Contents
Preface ............................................................................................................................................. i
Chapter 1: Wave Propagation........................................................................................................ 1-1
Wavelength, Frequency, and Speed of Sound ................................................................................. 1-1
Combining Sine Waves .................................................................................................................... 1-2
Combining Delayed Sine Waves ...................................................................................................... 1-3
Diffraction of Sound .......................................................................................................................... 1-5
Effects of Temperature Gradients on Sound Propagation ................................................................ 1-6
Effects of Wind Velocity and Gradients on Sound Propagation........................................................ 1-6
Effect of Humidity on Sound Propagation......................................................................................... 1-7
Chapter 2: The Decibel................................................................................................................... 2-1
Introduction ....................................................................................................................................... 2-1
Power Relationships ......................................................................................................................... 2-1
Voltage, Current, and Pressure Relationships.................................................................................. 2-2
Sound Pressure and Loudness Contours......................................................................................... 2-4
Inverse Square Relationships........................................................................................................... 2-6
Adding Power Levels in dB............................................................................................................... 2-7
Reference Levels.............................................................................................................................. 2-7
Peak, Average, and RMS Signal Values........................................................................................... 2-8
Chapter 3: Directivity and Angular Coverage of Loudspeakers ................................................ 3-1
Introduction ....................................................................................................................................... 3-1
Some Fundamentals ........................................................................................................................ 3-1
A Comparison of Polar Plots, Beamwidth Plots, Directivity Plots, and Isobars ................................ 3-3
Directivity of Circular Radiators ........................................................................................................ 3-4
The Importance of Flat Power Response ......................................................................................... 3-6
Measurement of Directional Characteristics ..................................................................................... 3-7
Using Directivity Information ............................................................................................................. 3-8
Directional Characteristics of Combined Radiators .......................................................................... 3-8
Chapter 4: An Outdoor Sound Reinforcement System ............................................................... 4-1
Introduction ....................................................................................................................................... 4-1
The Concept of Acoustical Gain ....................................................................................................... 4-2
The Influence of Directional Microphones and Loudspeakers on System Maximum Gain .............. 4-3
How Much Gain is Needed? ............................................................................................................. 4-4
Conclusion ........................................................................................................................................ 4-5
Chapter 5: Fundamentals of Room Acoustics ............................................................................. 5-1
Introduction ....................................................................................................................................... 5-1
Absorption and Reflection of Sound ................................................................................................. 5-1
The Growth and Decay of a Sound Field in a Room ........................................................................ 5-5
Reverberation and Reverberation Time............................................................................................ 5-7
Direct and Reverberant Sound Fields .............................................................................................. 5-12
Critical Distance................................................................................................................................ 5-14
The Room Constant ......................................................................................................................... 5-15
Statistical Models and the Real World .............................................................................................. 5-20