Table of Contents
Table of Contents ........................................................................................................ 1
Introduction ................................................................................................................. 3
Using This Manual............................................................................................................................. 3
Sound Basics ............................................................................................................... 4
General .............................................................................................................................................. 4
Wavelength and Frequency................................................................................................................ 5
Decibels ............................................................................................................................................. 5
Sound Pressure vs. Sound Power....................................................................................................... 6
Octave Bands..................................................................................................................................... 6
Human Response to Sound ................................................................................................................ 7
Sound Pressure Evaluation Criteria ................................................................................................... 8
Acceptable Sound Levels.................................................................................................................13
Sound Testing Methods ................................................................................................................... 14
HVAC Equipment Acoustics............................................................................................................ 15
Calculating Sound Pressure from Sound Power .............................................................................. 15
Outdoor Sound Analysis............................................................................................ 21
General ............................................................................................................................................ 21
Outdoor Sound Analysis Basics.......................................................................................................21
Open Field Analysis......................................................................................................................... 22
Sound Barriers................................................................................................................................. 23
Reflecting Walls...............................................................................................................................26
Indoor Sound Analysis – Zoned Comfort Systems ................................................... 28
General ............................................................................................................................................ 28
Sound in a Room ............................................................................................................................. 28
Room Constant and Sound Absorption Coefficient ......................................................................... 28
Thompson and Schultz Equations....................................................................................................31
Indoor Sound Analysis – Ducted Zoned Comfort Systems....................................... 35
Radiated and Discharge Sound Power ............................................................................................. 35
Multiple Path Concept ..................................................................................................................... 35
Duct Sound Path .............................................................................................................................. 36
Converting Ducted Sound Power to Sound Pressure ....................................................................... 40
Duct Breakout Sound Path............................................................................................................... 43
Return Air Sound Path ..................................................................................................................... 47
Diffuser Sound Path......................................................................................................................... 49
Radiated Sound Path........................................................................................................................ 51
Evaluating All the Sound Paths........................................................................................................ 52
Indoor Sound Analysis – Central Systems ................................................................ 53
General ............................................................................................................................................ 53
Multiple Paths.................................................................................................................................. 53
Central System Duct Sound Path.....................................................................................................54
Transmitted Sound........................................................................................................................... 63
Main Duct Breakout ........................................................................................................................ 66
Return Air Path ................................................................................................................................ 69
Regenerated Noise..................................................................................................... 73
General ............................................................................................................................................ 73
Evaluating Regenerated Noise......................................................................................................... 73
Conclusions............................................................................................................... 75
Appendix 1 - References .......................................................................................... 76
Appendix 2 – HVAC Equipment Sound Measurement Stds..................................... 77
General ............................................................................................................................................ 77
Appendix 3 – Various Acoustic Properties of Materials ........................................... 78
General ............................................................................................................................................ 78
