OITC vs. STC: What Rating System Should I Rely On?

If you’re shopping around for Soundproofing solutions, you’ve probably heard something about the OITC rating System. A relatively new way of measuring sound transmission, an OITC rating (which stands for Outdoor–Indoor Transmission Class) provides information about how well a barrier blocks against certain types of frequencies. But is it useful for you?


The Difference Between STC and OITC
Professionals have been using the STC rating System to measure sound transmission for decades. Originally used to evaluate transmission through interior walls only, today STC is used to assess almost all types of barriers: exterior walls, interior walls, Windows, and doors.

Developed in 1990, the OITC rating System was designed to measure the transmission of street sounds (such as car horns, sirens,construction, and low-flying airplanes) through exterior walls, Windows and façade elements. Exterior noise tends to be a lower frequency than interior noise (such as voices), so the OITC rating System emphasizes low frequency sounds in its calculations. Professionals use the OITC rating System less frequently than the STC rating System.

Today, the OITC rating System is used to assess any barrier meant to block out low frequency sound. For example, if your neighbor has a subwoofer-equipped sound System, you may want to consider OITC ratings for all of your barriers, interior and exterior.

How the OITC Rating is Measured
Like the STC rating System, OITC measures sound intensity loss in decibels. If a 105-decibel above ground subway only registers as 80 decibels after traveling through a Window or wall, the sound experiences a 25-decibel deficit. The ability of a barrier to create a specific decibel deficit varies according to the frequency of the sound passing through it: in general, very high and very low frequency sounds are more difficult to block.

A barrier’s OITC rating is measured using data gathered over an 80 to 4000 hertz frequency range. Once the data is collected, professionals calculate a barrier’s OITC rating in accordance with standards laid out by the American Society for Testing and Materials (ASTM). In general, a barriers OITC rating is lower than its STC rating.

What OITC Can Tell You About Your Windows
Because it weighs low- to mid-frequency sounds more heavily, OITC is a more appropriate rating System for Windows. The blares and beeps of heavy traffic, the roar of airplanes, and the rattle of trains all produce a low-frequency cacophony.

However, for the average homeowner, the STC ratings for windows are sufficient—and preferable. The OITC rating System is still in its infancy, and has yet to diffuse throughout the Soundproof Window industry. While perhaps a better measure of Soundproofing, you’re generally better off asking for a Window’s STC rating.

In addition to being more widely used, the STC rating System has agreed upon benchmarks that make it easy for laypeople to understand how the rating will impact noise transmission. When in doubt, ask for the window STC rating on your Soundproof Windows and barriers. It’s a clearer and more widespread measure of sound transmission.

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