You have probably heard of STC and IIC but what do these mean and measure in acoustics? In this blog we will cover the core acoustic measurements.
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).