The Book of Acoustics

Chapter 3.0 Types of acoustic treatment

3.3 Important acoustical treatment ratings

Acoustical rating systems provide guidance when it comes to understanding the efficacy of different treatment solutions. Here are some of the most important ones to familiarise yourself with.

Sound Transmission Class (STC)

Sound Transmission Class (STC) is a numerical rating used to indicate how effectively a given building material blocks sound from transmitting through it. STC is used to rate partitions or dividers, as well as floors, ceilings, doors and windows. Generally, a low performance rating is less or equal to 35, while a high performance rating is greater or equal to 55.

Noise Reduction Coefficient (NRC)

A Noise Reduction Coefficient (NRC) is a single number index rating that indicates the ability of a given material to absorb sound. Based on an average of individual sound absorption coefficients in the mid-frequency range, an NRC of 0 indicates perfect reflection while an NRC of 1 indicates perfect absorption. NRC is commonly used to rate acoustic wall panels, ceiling tiles, baffles, banners and office screens.

Sound Absorption Class

Sound Absorption Class ratings are used to enable comparison of the absorption performance of different acoustic products. The classes are classified with letters ranging from A-E. The class ratings are obtained by measuring a product’s absorption coefficient values over a range of frequencies. These values are then compared against a reference curve to obtain a weighted sound absorption coefficient. An acoustic product with an A rating has the highest sound absorption performance. However, an A rating is not necessarily better than a B rating in certain cases. The absorption class you select ultimately depends on which frequencies you need to absorb.


The Book of Acoustics

This is a handbook for architects and interior designers who want to create acoustically beautiful spaces that make people feel happier, healthier and more productive.