Basic Documentation
Table Of Contents
- About this Application Guide
- Chapter 1–Introduction
- Chapter 2–Physics of Sound
- Chapter 3–HVAC Sound Sources
- Chapter 4–HVAC Sound Attenuation
- Introduction to HVAC Sound Attenuation
- Plenums
- Duct Attenuation
- Duct Takeoffs and Divisions
- Duct Silencers
- End Reflection
- Environment Adjustment Factor
- Space Effect
- Radiated Sound Attenuation
- Chapter 5–HVAC System Sound Analysis
- Chapter 6–Minimizing HVAC Sound
- Appendix
- Glossary
- Index
Chapter 2–Physics of Sound
(See the Appendix for a copy of this graph that is suitable for reproduction.)
Figure 5. Noise Criterion Curves.
RC Curves
The Room Criterion (RC) rating is a more recent development for analyzing and rating the
sound present in a room. The RC rating should be used, whenever possible, in specific
design applications since it is superior to the NC curves for the following reasons:
1. The RC curves extend down to 16 HZ that covers the low frequency sound spectrum
more completely than the NC curves.
2. Establishing the applicable RC curve that applies to an actual sound profile is dependent
on the overall shape or profile of the actual sound curve, rather than merely the highest
penetration of the sound into the NC family of curves.
3. Since a given sound curve is likely to have a unique curvature or profile, each RC sound
curve is further annotated as to its actual characteristics:
• A curve with a rumbly (low frequency) component is also given an R suffix.
• A curve with a hissy (high frequency) component is also given an H suffix.
• A more neutral curve without a rumbly or hissy component is given an N suffix.
18 Siemens Building Technologies, Inc.