The sound reduction index is a reflection of the acoustic insulating properties provided by a material. Several standardized methods can be used to develop a sound reduction index that will be readily understood by observers anywhere in the world. Companies test products designed for acoustic insulation before sale, and label the packaging so buyers understand what kind of insulation is available. This can be important for purchasing decisions, as people want to select acoustic insulators that will meet their needs.
One simple method to test products is to use two rooms with an opening between them. Technicians can place a sample of the test material in the opening and use a noise source to produce standardized noise. Tools in both rooms measure decibel levels, frequencies, reverberation, and other characteristics of the sound. The researchers can compare the data between the room with the noise source and the target room to determine how much sound reduction the material offers. This allows them to create an index to provide information about the insulating properties of the test material.
Concerns surrounding acoustic insulation can vary. In a setting like a radio booth, operators want no outside noise to penetrate, because it could interfere with the quality of the broadcast or recording. Materials with a very high sound reduction index are necessary, and they should have a broad scope, limiting not only most decibel levels but also a range of frequencies. This will prevent all but the loudest of noises in all frequencies from penetrating the booth.
For other settings, the sound reduction index may concentrate more on frequencies than decibel levels. Using noise filtering, for instance, it may be possible to cut out specific frequencies from recordings and other activities, and thus it is acceptable if they bleed into an environment. For settings like freeway barriers, vibration may also be a cause for concern, and it is necessary to develop a material that resists noise as well as vibrations from heavy cars and trucks.
The use of standardized techniques and measurements for sound reduction index values is important. A material with a standardized rating can be used in any setting around the world. A sound technician will get the necessary information about its properties from the packaging and can decide if it will be appropriate for a project. When technicians use methods that are not standardized, it can create problems, as only people familiar with those methods will understand what the index actually means.