Question & Answer : Acoustic Tests

IIC & STC tests

Tested in a controlled lab environment

test-iic-stc-acoustiques-anechoiqueThe insulation of sounds and impact noises between the rooms of the house and between units of a condominium or apartment building is a very important factor for the floor covering industry.

When assessing noise reduction features, audio consultants, architects and other specialists rely on acoustic tests to determine the performance of flooring products, particularly subfloor membranes.

In North America, the data generated by the methods used to evaluate sound travelling and their comparisons can be misleading. We will attempt to demystify for you, these acoustic tests and their results.

These tests, use to evaluate the distribution of sound, are made in a controlled environment (laboratory).

IIC tests

The IIC tests the ability to block impact sound by measuring the resistance to transmission structure-borne noises with simulation of foot steps or objects dropped on the floor from a certain height.

STC tests

STC tests refers to the ability to reduce airborne sounds. It evaluates the diffusion of sounds in the air such as voices, stereo systems and TV set.

Technique behind IIC and STC tests

Both tests use a standardized instrument that measures the performance being guided by a system that analyzes the sound transmission in a lower chamber and an upper chamber. The measurements obtained (decibels) are combined to a mathematical algorithm to determine the test result. The higher the number, the higher the resistance.

FIIC & FSTC tests

Performed in existing building

The FIIC test measures the diffusion of impact noises in real environment and the FSTC test measure dissemination of airborne noises in real environment. Both tests being performed in an existing building rather than in laboratory .

The National Building Code requires a score of 50 or more for the FIIC and recommends (not require) a result of 55 or more for the FSTC.

Figure 1. In actual building (FIIC). FIIC factor depends mostly on the materials used for the construction of the building.

Figure 2. In a lab (IIC). Tests in laboratory give more precise due to assembly quality and controlled environment.

Because of all the different building materials available today, it is not surprising that the results of these tests are highly variable depending on the different floor/ceiling assemblies.


IIC; impact sounds, measured in lab.
STC; airborne noises, measured in lab.
FIIC; impact sounds, measured in an existing building.
FSTC; airborne noises, measured in an existing building.


The acoustic performance will vary depending on the type of building, structure assembly, type of subfloor, ceiling type, type of insulation, type of piping (plumbing), type of flooring, type of underlayment membrane, etc.

In short, it is only if all the materials used are the same in each test (both in laboratory and existing building) that the results will be precisely comparable and will indicate, among others, the actual acoustic performance of an underlayment membrane compare to another.The actual acoustic performance of a subfloor membrane is difficult to quantify precisely , but the tests in question still provide a good indication of their performances.