Basic Documentation

Glossary
attenuate, attenuation
To decrease the sound power level resulting in a lower sound pressure level at the point of
concern. Also see insertion loss.
background sound
Sound from sources other than the one being measured or analyzed. In a room being
analyzed for HVAC sound, background sound may typically include cooling fans on electronic
equipment, copy machines, conversation, and even outside sources such as traffic, etc.)
broadband sound
Sound that is composed of frequencies covering much of the entire audible range as
opposed to tonal sounds that are composed of a narrow frequency range.
C-Weighted Sound Level
A method of ambient sound measurement that provides uniform weighing of frequencies
between 70 and 4,000 Hz, but reduces the effect of frequencies above and below this range.
C-Weighted measurements are much closer to true sound pressure levels than A-Weighted
sound level measurements.
decibel (dB)
When used in conjunction with acoustics, it’s an expression of the relative strength or
intensity of the sound power level or sound pressure level. The unit is based upon the
logarithmic scale so that a 50 dB sound power level actually represents an energy level that
is 100 times greater than that of a 30 dB sound power level.
dosimeter
An instrument for registering the occurrence and cumulative duration of sound that exceeds a
predetermined level at a specific location. A Dosimeter is most typically used when analyzing
an area with regard to ensuring compliance with allowable noise exposure limit regulations.
end reflection
The return of sound power energy back into a duct system when the duct ends abruptly or
undergoes an abrupt change in area. When end reflection occurs, the sound pressure level is
reduced in the area that the duct serves. Thus, when a duct terminates at a room diffuser,
end reflection will cause a reduction of the sound power that would otherwise enter the room.
fan sound power
The sound power that a fan radiates into a standard test duct. Fans are tested for and
certified as to their sound power level by the Air Movement and Control Association (AMCA).
112 Siemens Building Technologies, Inc.