Building, Design for Sound and Acoustics, Part 4, Understanding Sound Transmission (STC) Ratings

Building, Design for Sound and Acoustics, Part 4, Understanding Sound Transmission (STC) Ratings


A fundamental understanding of the rating of Sound Transmission Class (STC) is an essential ingredient in the correct planning and design of any public space or room. If you are concerned about transmission of sound from one room to another the tool STC rating is used for measuring the efficiency of a material or ability of soundproofing system to achieve your goal.


This article has information on understanding and applying measurements of Sound Transmission Class (STC) to facility or room soundproofing. The STC is a measure of the ability of materials to obstruct sound from transmitting from space to space. If comfort or privacy of guests is a worry a level of soundproofing must always be considered during the planning and construction stage of both private and public spaces. When sound energy comes into the building structure it will transmit from room to room. This is known as Structure Borne Transmission. The objective is to control the sound energy inside the space and better the experience quality of the occupants utilizing the facility.


All materials and products utilized in application of soundproofing a facility or room will use one among the following measurement forms;


1) NRC (noise reduction coefficient)

2) STC (sound transmission class)

3) MTC (music transmission class)

4) OITC (outdoor indoor transmission class)


The rating of STC is used most commonly in sound suppression or soundproofing.


Let us look into few facts about the STC rating. Do not be fooled by a material’s high ratings. Everything is not as it appears. The rating of STC is specified as an average of the way the material will function at frequencies from 125 Hz (bass) to 4,000 Hz (treble). Generally this will be specified as a solitary number reference (STC 54). There is more transmission of sound energy from the lower frequencies. This is clearly evident when you hear the car adjacent to you rattling and booming while the adolescent is listening to the most recent hip hop music. The sound waves of higher frequency have much less energy and therefore more easily controlled within a room.


Quick Points


1) The rating of STC is an average of the way a soundproofing material will function over an array of sound frequencies.


2) The rating specifies the ability of soundproofing materials to reduce sound levels from 125 Hz (bass) to 4,000 Hz (treble).


3) For higher rating the overall average material’s performance is better.


4) Decibels (db) are used for measuring the rating.


5) There will be a difference in the performance of soundproofing materials based on the frequencies it receives.


The continuation of this is given in the next part titled ‘Building, Design for Sound and Acoustics, Part 5, Understanding Sound Transmission (STC) Ratings’.

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