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Sound and Flooring

A graphic depiction of a ripple or a sound
transmission wave

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

A hand-held sound level meter measures sound

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).

ASTM Internatioanl Standards
Organization Logo

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

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.