The transfer of sounds through walls, ceilings, and floors can result in rather annoying and unwanted noise in your living
area, work area, and other areas where confidentiality is a must. In addition, the reflection of sound in a room can create
echoes, garbled audio, and reduce speech clarity. Examples where proper sound transmission is crucial include the offices of
doctors, lawyers, counselors, human resource departments, home theatres, auditoriums, and so on.
How Sound Works
Sounds are created by ripples or vibrations in the air called sound waves. Sounds waves can vary in pitch and in loudness
or strength. The loudness of a sound is measured in decibels (dB). Louder, stronger sounds have higher decibel ratings than
soft, quiet sounds. To give you an idea, the human voice ranks in around 50 dB.
Pitch is determined by the frequency of the sound wave. For example, deep or low pitch noises are created by waves that
are long and slow, while high pitch noises are short and fast. The frequency of a sound wave is measured in waves per second,
or hertz (Hz). Humans can only hear frequencies between approximately 20 Hz and 20,000 Hz (or 20 kHz). If you've ever
wondered why you can't hear a dog whistle, this is why. Dog whistles produce sound waves that are so high pitched that they
rate over 20 kHz.
About Sound Transmissions and Sound Absorption
Impact Sound Transmissions (A.K.A. Structure Sound Transmissions) are transmissions of vibrations that result from impact
to the floor covering. This includes walking, jumping, dropping objects, and moving furniture. These vibrations can travel
through the floor, subfloor, and ceiling of the room below. They can generate sounds in both rooms, which can be rather
distracting and annoying. The type of flooring system used can have a large impact on the level of these sound transmissions
to lower levels. For more information on measuring and reducing impact sound transmissions, click on the Impact Insulation
Class (IIC) link below.
Airborne Sound Transmissions include sound transmissions made by airborne vibrations. Airborne vibrations
can come from speech, television, music, airplanes, cars, trains, mechanical equipment, and so on. Airborne sound
transmissions can travel through floors, ceilings and walls, and can also travel through air vents, under doors, through
windows, and other openings. To learn more about measuring and reducing airborne sound transmissions, click on the Sound
Transmission Class (STC) link below.
Sound Absorption is the ability of a material to absorb sound rather than allowing it to reflect around
the room. Sound absorption occurs when sound strikes the pores of a surface and is converted into heat energy. Increasing
sound absorption reduces echoes and can increase sound clarity in a room. This is especially important in areas like
amphitheatres, auditoriums, restaurants, and home theatres, where good sound acoustics are needed. To learn more about
measuring sound absorption, click on the Noise Reduction Coefficient (NRC) link below.
About Sound Rating Systems
With the different types of sound transmissions that are produced, it is not surprising that there are three different
methods used for rating the acoustical properties of a structure: Impact Insulation Class (IIC), Sound Transmission Class
(STC), and Noise Reduction Coefficient (NRC).
Each of these ratings uses a different method set forth by the American Society for Testing and Materials (ASTM) to
determine a different type of sound rating. Of the three sound rating systems, the IIC rating focuses the most on flooring.
While the STC and NRC ratings cover a wide variety of noise control materials besides flooring, they are still important to
know about as their ratings are affected by the type of flooring in a structure.
To learn more about each sound rating system and how to find the right flooring materials to fit your sound related needs,
click one of the links below or in the navigation to the left.
Impact Insulation Class Rating
(IIC) – Sound
Transmission Class Rating (STC) – Noise Reduction Coefficient Rating (NRC)
To learn more about the different ASTM testing methods used for each sound rating system, visit www.astm.org.
Building A Floor/Ceiling System With Sound In Mind
The sound transmission rating of a floor/ceiling system can be determined by not only the floor covering in use but also
the subfloor, underlayment, flooring joists, ceiling below as well as adhesives and sealants that may be needed for
installation. Other sound–deadening additions that are used in floor/ceiling assemblies include, but are not limited
to, insulation in between wood floor joists and resilient channels connect to the ceiling. Visit the section on Sound Controlling Floor/Ceiling
Materials to learn more.