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
Sound Measurement Worksheet
frequency
When applied to sound, it’s the number of complete pressure wave fluctuations per second.
The measurement unit is cycles per second called Hertz (Hz). Human hearing allows us the
hear sound within the range of about 20 Hz to 20,000 Hz.
insertion loss
The reduction in sound power level due to the physical ability of something to absorb or
dissipate sound power. Also see attenuation.
octave band
A limited range of sound frequencies for the purpose of acoustical measurement and
analysis. To reduce the amount of individual frequencies that need to be measured when
analyzing a sound source, the 20,HZ to 20,000,Hz frequency range of human hearing is
divided up into what’s referred to as standard octave bands. These bands are used by
virtually everyone in the industry for consistency in specifying sound power levels and
measuring sound pressure levels. The standard bands are identified by their mid frequency:
16, 31.5, 63, 125, 250, 500, 2,000, 4,000, and 8,000 Hz. The bands have been selected so
that each band covers the frequency range where its lowest frequency is one half of its
uppermost frequency. Thus, the 125 Hz band covers from 84 to 167 Hz, while the 250 Hz
octave band covers from 167 to 334 Hz.
one third octave bands
For very precise laboratory sound measurement and analysis, the standard octave bands are
each further divided into three narrower bands. (This is used by the AMCA sound
measurement laboratory when determining certified fan sound power level ratings.)
sone
A linear unit of loudness as experienced by the human ear at a frequency of 1,000 Hz.
sound masking
Sometimes also called white noise. It is the intentional addition of a background sound that
tends to provide just enough broadband intensity to cover background sounds. In office
environments, a well designed HVAC system provides sufficient sound masking due to its
sound. The background sound used for sound masking should ideally not be noticeable
when present, and must not be at an objectionable level (too loud) or have identifiable tones.
sound power level
The power (dB) rating of a source of sound energy that is an indication of its potential for
loudness.
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