Understanding Sound Control

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Types of Sound Control

Two General Classifications of Sound or Noise:

Ambient Noise, or Airborne Sound, includes conversation, television, radio, dog barking, etc.  This type of sound is measured by its Sound Transmission Class (STC).

Impact Sound is the resulting vibration or noise created when objects collide with the flooring surface, such as heels when walking or running on the floor, dropping items on the floor, a bouncing ball, dragging a chair across the floor, etc.This type of sound is measured by its Impact Insulation Class (IIC).

ASTM International

ASTM International was organized in 1898, and is one of the largest voluntary standards development systems in the world.  ASTM stands for American Society for Testing and Materials.  ASTM International is a not-for-profit organization which provides a forum for producers, users, ultimate consumers, and those having a general interest (representatives of government and academia) to meet on common ground and write standards for materials, products, systems and services.  ASTM has developed the standards for sound testing of floor systems.

Working with ASTM Test Numbers

The STC, FSTC, IIC, ∆IIC, and FIIC test results are expressed as a single dB (decibel) value.  The value is the result of calculations across a full range of sound frequencies starting at 63 hertz up to 5,000 hertz.  Higher dB values indicate better sound reduction.  Since these are logarithmic calculations, increases from 40dB to 45dB are easier to achieve than increases from 50dB to 55dB, or 60dB to 65dB.

The Sound Transmission Class (STC) value of a floor assembly is primarily a function of mass.  For example, an eight inch concrete slab will be better than a six inch concrete slab for reducing sound transmission.

The Impact sound transmitted by a floor is a function of how well it absorbs sound vibration caused by an impact.  This is measured as the Impact Insulation Class or IIC.  Carpeting is the best impact absorber, wood less, and ceramic tile or marble the least absorbing.  Think about dropping an object on the finished floor like a wine glass.

The Delta IIC measures the Impact Class improvement for a specific “total” floor assembly.  This test is only performed on a six inch concrete slab without a ceiling assembly.  The result for the tested floor assembly (underlayment materials and the finished floor surface) is compared with the “bare” six inch concrete slab IIC value.  In order to understand the IIC improvement, you need to know the finished flooring surface as well as the sound underlayment and adhesives used in the floor assembly tested.  Most important, Delta IIC values are NOT additive.  For example, if the underlayment material claims a ∆IIC of 15dB and a thin set or adhesive manufacturer claims a ∆IIC of 10dB, having both in the same floor assembly will not result in an IIC improvement of 25dB.  Make sure you know how the product was testing, including the finished flooring and other floor assembly components.

Field testing is an excellent way to establish the Sound Transmission Class (FSTC) or Impact Insolation Class (FIIC) of a specific floor assembly and building.  The result is specific to the tested room and should not be used to grade or measure a particular component (underlayment, adhesive, thin set, etc.).  Laboratory sound testing is conducted in a controlled environment and field testing is not.  As a result, field test results can be misleading.  The specific construction, temperature, humidity, or room content can influence the result.  For example, was a perimeter isolation barrier material used to isolate the room?  Was the air conditioning on or off?  Was anything in the room like drapes or furniture, etc.

5 Key Factors of Floor Sound Performance

The sound performance of a floor/ceiling assembly in a building is the result of 5 key components of the structure.  These construction components will dictate the underlayment product and associated materials specified.

(1)    Sub-Floor Construction – This could be concrete slab at various thicknesses (for example, 6 inches or 8 inches thick), wood joist and wood truss systems, or a combination structure of concrete, metal & wood.


(2)    Finished Flooring – Ranges from hard surface flooring like ceramic tile, stone, marble and natural wood, to soft surface flooring like carpet and luxury vinyl tile.


(3)    Ceiling Type – Concrete Slab construction could have no ceiling included, a ceiling system attached directly to the bottom of the slab, or a suspended ceiling.  Suspended ceilings are generally either gypsum board with plaster or “architectural” ceiling board held in place with a metal grid system.  Wood joist and truss systems would include a ceiling unless it is “open” beam construction.


(4)    Air Plenum – Is the space created by the ceiling attached to the sub-floor structure.  The depth of the air plenum and its use, such as to include insulation material, recessed lighting, electrical wiring, HVAC duct work, etc. determines its value in reducing sound.


(5)    Isolating the Room – This is a critical construction component often overlooked.  Perimeter Isolation Barrier (PIB) material and sound absorbing caulking should be used to prevent sound “flanking” around the floor assembly.  Also, adhesives are better than using nails or screws which will transmit sound through the floor assembly

So as the architect, contractor, owner/user of the room, each step in the process of creating the specific condominium, office, home impacts the sound reducing and insulating performance of the total floor assembly.  How is the building designed?  How did the contractor build/install the components?  What finished flooring was selected by the designer/decorator/end user?

ASTM Tests for Floor Assembly Sound Performance

Sound testing can be done in an approved laboratory or in the field (on site).  Laboratory testing is the most un-bias measurement of flooring systems and products.  The laboratory test results provide an excellent way to evaluate, compare and select materials.  Field tests provide sound measurement of specific rooms or floor assemblies, but are unique to the test location and not suitable for comparing products and materials.

STC – Sound Transmission Class (ASTM E 90)
IIC – Impact Insulation Class (ASTM E 492)
∆IIC – Delta Impact Insulation Class (ASTM E 2179)
FSTC – Field Sound Transmission Class (ASTM E 336)
FIIC – Field Impact Insulation Class (ASTM E 1007)

Note: ASTM test procedures are periodically updated and the last update is listed after the test number, for example ASTM E 90-04 where the 04 means this test procedure’s latest update or change was in 2004.

Ranking Finished Flooring Surfaces

In general, Hard Surface flooring, those with greater mass density (weight) provide better sound transmission values (STC), that is, they are better at reducing ambient sound between rooms.  And Soft Surface flooring materials provide better impact sound reduction or IIC values.

Hard Surface Flooring
Natural Stone and Marble
Ceramic, Quarry & Porcelain Tiles

Intermediate Range
Laminates with foam backing
Floating Floors

Soft Flooring
Vinyl with foam backing
Luxury Vinyl Tile & Planks