N

Near Field
An area relatively close to the source of sound in which the sound pressure level varies(fluctuates) greatly with distance from the source.

Node
Point of no vibration

Noise
Unwanted sound

Noise Criteria Curves (NC)
A numerical rating system or family of curves used to specify background sound levels over a specified frequency range.

Noise Insulation Class (NIC)
A rating of the measured room-to-room noise reduction.

Noise Reduction (NR)
The reduction in the level of unwanted sound by any of several means for instance, by distance in outdoor space, by boundary surface absorption, by isolating barriers.

Noise Reduction Coefficient (NRC)
The arithmetic average of the sound absorption coefficients of a sound-absorbing material at 250, 500, 1000, and 2000 Hz rounded to the nearest 0.05.

Null
A minimum pressure region in a room.