A Practical Guide to Understanding the Basics of Acoustics and Sound Measurement

When creating comfortable and functional interior spaces, understanding acoustics is essential. This guide will provide you with the basics of acoustics, including how sound is measured and what the various values represent.

How People Perceive Sound and Loud Noises

To begin, it's important to grasp how sound is perceived by people. Studies have shown that a sound is perceived as twice as loud when the sound level increases by 10 decibels (dB). This example helps explain why small changes in sound levels can have a significant impact on our comfort and experience within a space.

Sound Transmission in New Zealand: STC and IIC

In New Zealand, the primary measurements used to evaluate sound transmission between floors are the Sound Transmission Class (STC) and the Impact Insulation Class (IIC). These measurements address different types of sound:

• Sound Transmission Class (STC): This measures the sound insulation of a floor/ceiling assembly against airborne sounds, such as talking or music playing. STC is measured in decibels (dB), with higher STC values indicating better sound insulation.
• Impact Insulation Class (IIC): This measures the sound insulation of a floor/ceiling assembly against impact sounds, such as footsteps. IIC is also measured in decibels, using a calibrated tapping machine that generates impact sounds at different frequencies. Like STC, higher IIC values indicate better performance.

Understanding Delta IIC (△IIC) Values

Delta IIC (△IIC) values represent the improvement in impact sound isolation that a specific product brings to a construction. It is calculated by taking the difference between the overall IIC value and the initial IIC value before the product was added. These values are typically measured using ASTM E2179, which requires the measurement to be taken using a concrete floor. 

This means that △IIC values are particularly relevant when considering flooring products for builds that include a concrete floor.

Key Considerations:

For those involved in the design and specification of buildings, especially timber structures, it's crucial to look beyond just △IIC values. Instead, focus on fully tested assemblies to ensure the acoustic performance meets the desired standards. This approach will help you achieve the best sound insulation and comfort in your interior spaces.

By understanding these basic principles of acoustics and sound measurement, you can make informed decisions that enhance the acoustic environment of your spaces, providing greater comfort and functionality for occupants.

Acoustic Terminology Cheat Sheet: 

• dB: the unit used to measure sound levels. 
• STC: Sound Transmission Class, measures airborne sounds.
• IIC: Impact Insulation Class, measures impact sounds.
• (△IIC)or Delta IIC: values represent the improvement in impact sound isolation that a specific product brings to a construction. 
• FIIC: The ‘field’ or in situ measurement of Impact Insulation Class.
• C_tr: A sound insulation adjustment. 
• R_w: 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. 
• L_n,_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 L_n,w, the better the acoustic performance.
• Impact sound: sound caused by physical impact e.g. footsteps
• Airborne sound:sound waves traveling through the air to your ear e.g. talking 
• Flanking sound: Flanking sound refers to noise that travels along indirect paths, such as through walls, floors, or ceilings, rather than directly through the primary barrier intended to block sound.