3M DL, SE NCB Balanced Noise Criterion Curves, Noise Criterion Curves NC, Noise Rating Curves NR

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Appendix B

NCB (Balanced Noise Criterion Curves )

This is the most recent incarnation of the curves based on Beranek’s work (1987). This curve family goes beyond a simple tangency method to try to ensure a more neutral characteristic to the noise spectrum and also accounts for speech interference such as: rumble, rattle, and hiss. NCB was recommended for use with HVAC systems and similar applications and accounts for lower frequency sounds in comparison to NC curves.

When setting NCB as the type on the meter, you should use S12.1 unless a local ordinance or similar requirement specifies the use of a tangency technique. (This is usually specified in a standard.)

Noise Criterion Curves (NC)

With NC curve evaluation, sound is measured in octave bands in 8 octave bands ranging from 63 to 8000 Hz and is then plotted on the octave band spectrum using a set of curves.

NC curve evaluation uses a tangency method. A tangency method is a process of comparing your measurements to a fixed curve. The correct curve number is the lowest curve that meets or exceeds the measured octave values. Typically, this is used in HVAC applications.

Noise Rating Curves (NR)

This curve family is a tangency technique and is used primarily in Europe and Australia. It is used not only for HVAC and machine noise applications, but also in community noise enforcement.

Noise Floor

The signal magnitude at the bottom of the instrument’s linear range. Input signals below the noise floor cannot be differentiated from the internal noise of the instrument.

Overload (OL)

An overload will occur whenever the input signal exceeds the dynamic range of the instrument.

Pascal (Pa)

Unit of pressure equal to 1 Newton per square meter.

Models SE and DL