Author: Site Editor Publish Time: 2022-08-11 Origin: Site
This is the most common rating used in North America for determining airborne sound transmission loss between 125 and 4,000 Hz. This range covers the majority of common noises we hear including speech, television, music, dogs barking, and other similar annoyances. A higher STC rating often shows improved performance. However, the rating is essentially an average over the 16 frequency points tested.
Because of this, a product can perform exceptionally well in one range, poorly in another, and still end up with a better STC rating than a competing product that may have performed better in a frequency range more relevant to your project requirements.
This is a pretty common occurrence that should not be ignored when comparing products. Sort through the misleading ratings by gaining access to actual sound test data showing the STC contour line on the transmission loss graph. The performance in relation to the STC contour line will reveal the consistency of the product over the most common frequencies.
A good level of isolation for walls and ceilings is STC 50 plus. A high level of isolation for walls is STC 60 plus with ceilings at STC 50 plus.
The original purpose of the OITC rating was to determine performance of products in relation to exterior noise, which is often heavy in low frequencies. We also use the OITC rating to determine a product’s value for use in low frequency sensitive areas such as home theaters and recording studios. The OITC rating represents transmission loss results from 80 to 4,000 Hz using a different mathematical equation than the STC rating. The results express in decibels as opposed to the point system used to determine STC ratings and with weighting more towards low frequency performance. A higher number shows better performance.
Acoustic labs conduct the IIC test using a tapping machine with steel faced hammers. These hammers strike a test floor material generating sounds between 125 to 4,000 Hz. The impact creates vibrations that travel through the floor into the receiving side (the room below). The engineer plots the results of each tap on a graph, compares the results to the reference assembly, and determines the IIC rating from comparing these two tests. A higher number shows better performance. The IIC rating does not account for any squeaking or rattling caused by loose wood frame construction. Nor does it account for low frequency footfall noise or structural deflection.
An IIC rating of 50 and above is most common in building code and HOA requirements.
