SoundPro Noise Curves Firmware
Simple SPL measurements do not represent the background noise our ears hear. Because our ears are less sensitive to low frequency noise than to high frequency noise, noise levels at higher frequencies must be given more weight than levels at lower frequencies. The result is a set of curves called Noise Criterion or NC curves.
Noise Curve tests are based on standard NC or NCB (balanced noise curves), RC (Room Criteria), and PNC (preferred noise curve) ANSI tests.
NC (also known as NCB, or balanced noise curves): Noise value is based on ANSI standard S12.2-1995 (ASA 115-1995) Criteria for Evaluating Room Noise. It uses ANSI Class 1 octave-band filters to divide the sound spectrum into 9 octave bands, measuring the SPL level of each band. Then, the results are compared to a table of values defined in the specification. The table lists noise criteria numbers by row, with each row having values defined for each octave band. The NC band is defined as the lowest band number for which none of the octave-band SPL values for the row are exceeded.
RC (Room Criteria): Noise based on the same ANSI standard but with a different table of values primarily to rate noise in offices. This system was not intended for use in very quiet spaces below RC 25. Typically, RC is used in evaluating HVAC systems, while NC is used for more general purposes, including motion picture theater spaces and offices.
PNC (preferred noise criteria): This computation was derived by Beranek, Blazier, and Figwer in 1971, but is not based on an ANSI standard, and has not been widely accepted.
Transmission Loss is used to measure the amount of sound isolation that a partition provides.
Typically, a noise source is placed on one side of the partition, and the room noise level is measured in 1/3 octave bands, sometimes at more than one point.
Then, the measuring device is moved to the other side of the partition (presumably in another room) and the same measurement is taken.
Then, the transmission loss (TL) at each 1/3 octave bands is computed, and a formula is applied to derive a numeric number representing the relative noise reduction of the partition. This number can be used to effectively compute the amount of reduction in sound level that a partition (wall) will provide in actual use.
Measures noise in a room and characterizes it to a numeric value taking into account how the human ear hears. 