Acoustic Terminology

A

Absorption: The process by which a material, structure, or object takes in sound energy when sound waves are encountered, rather than reflecting it.

Airborne sound: Sound waves travelling through the air to your ear (e.g., talking).

ASTM: ASTM International, formerly known as the American Society for Testing and Materials, is a standards organisation that develops and publishes standards. This is the standard used in NZ.

C

Ctr: A sound insulation adjustment.

D

Damping: The loss of energy in a vibration system, usually through friction.

dB (Decibel): The unit used to measure sound levels.

Decoupling: A construction method that physically separates two structures to prevent sound transmission.

(△IIC) or Delta IIC: Represents the improvement in impact sound isolation that a specific product brings to a construction.

Diffusion: The scattering of sound waves to create a more uniform sound field, reducing echoes and hotspots.

F

FIIC: The ‘field’ or in-situ measurement of Impact Insulation Class.

Flanking sound: Noise that travels along indirect paths, such as through walls, floors, or ceilings, rather than directly through the primary barrier intended to block sound.

Floating floor: A floor system designed to reduce impact sound transmission by incorporating an isolation layer.

H

Hertz (Hz): The unit of frequency or the speed of vibration of a sound wave. Synonymous with “cycles per second” (CPS).

I

IIC (Impact Insulation Class): Measures impact sounds.

Impact sound: Sound caused by physical impact (e.g., footsteps).

ISO: ISO adopts the consensus system, whereby it is allowed to establish standards through agreement among its members. ASTM, on the other hand, has a different structure along with a different approach to developing international (or consensus) standards.

Isolation: Resistance to the transmission of sound by materials and structures. The separation of airborne or mechanically transmitted energy.

L

Ln,w (Weighted, Normalised Impact Sound Pressure Level): A single-number rating of the impact sound insulation of a floor/ceiling when impacted on by a standard ‘tapper’ machine. Ln,w is measured in a laboratory. The lower the Ln,w, the better the acoustic performance.

R

Reflection: The bouncing back of sound waves when they hit a surface.

Resilient channel: A metal channel used in wall and ceiling assemblies to improve sound isolation by decoupling layers of drywall.

Reverberation: The persistence of sound in a space due to multiple reflections off surfaces like walls, ceilings, and floors.

Reverberation Time (RT60): The time it takes for sound to decay by 60 decibels in a given space.

Rw (Weighted Sound Reduction Index): A single-number system used for quantifying the transmission loss through a building element. Rw is based on the amount of sound that can be transmitted through a noise wall.

S

Sound masking: The introduction of background sound to reduce the intelligibility of speech and improve acoustic privacy.

STC (Sound Transmission Class): Measures airborne sounds.

T

Transmission Loss (TL): The reduction in sound energy as it passes through a barrier, typically measured in decibels (dB).