Sound Absorption Coefficient – What is it?
The sound absorption coefficient is a crucial parameter that measures how much acoustic energy is absorbed by a given surface or object. Denoted by the Greek letter Alpha (α), this coefficient ranges from 0 to 1. A value of 0 indicates that all sound is reflected, while a value of 1 means that all sound is absorbed by the object. The absorption coefficient is influenced by two primary factors:
- Frequencies: The same material will absorb sound differently depending on the frequency of the sound waves.
- Angle of incidence: The absorbing properties of an object can vary based on the angle at which the sound waves strike it.
The Importance of the Sound Absorption Coefficient
This coefficient is vital in various applications, especially in room acoustics and the construction of anti-noise solutions. For instance, in interior acoustics, sound absorption by surfaces reduces reverberation within a room. In industrial settings, materials with specific absorption properties are used to build enclosures and barriers or silencers.
Sound Absorption Coefficient – What Does it Depend On?
The sound absorption coefficient is measured in 1/3 octave or 1 octave bands, as it varies with the frequency of the sound. To account for different angles of sound incidence, the reverberation absorption coefficient, an average value for all angles, is often used. Additionally, the type of material, its thickness, and its structure (especially if it comprises multiple layers) play significant roles. The location of the absorbing material relative to hard reflecting plane is also crucial, particularly in interior design.
Sound Absorption Coefficient – Why is it Important?
The sound absorption coefficient is a foundational element in room acoustics, impacting not just residential spaces but also areas with specialized uses. It directly affects the reverberation time, a key parameter in defining the acoustic characteristics of a room. In specialized settings like lecture halls, concert halls, or recording studios, the significance of the sound absorption coefficient is even greater.
Sound Absorption Coefficient – Where Does it Matter?
The importance of the sound absorption coefficient extends across various domains. In construction and design, it is regulated by standards such as the EN ISO 354, which specifies how to measure the reverberation sound absorption coefficient for large samples in a reverberation chamber.
Sound Absorption Coefficient and the EN ISO 354 Standard
As with most crucial parameters in construction and building, specific legal standards apply. Standard EN ISO 354 outlines the methodology for measuring the reverberation sound absorption coefficient for large samples (starting from 10 m²) in a reverberation chamber.
Sound Absorption Coefficient and the EN ISO 354 Standard
The EN ISO 11654 standard is used to calculate the practical sound absorption coefficient, converting measurements from 1/3 octave bands to 1 octave bands. This standard helps avoid method errors, such as results indicating more than 100% sound absorption. It also defines the classification of materials based on their absorption properties.
What are Sound Absorption Classes?
Absorption classes, derived from applying standard EN ISO 11654, provide a weighted sound absorption factor expressed as a single value, independent of frequency. These classes, marked with alphabet letters, help in categorizing sound-absorbing materials, which is particularly useful in the building materials industry.
What Classes of Sound Absorbers are There?
Absorption classes range from A to E, with A representing the best sound-absorbing materials. Lower performing materials are marked as unclassified. This classification system helps organize and standardize the extensive range of sound-absorbing products available.
Sound Absorption Coefficient – How to Calculate?
The reverberation sound absorption coefficient is measured in a reverberation chamber through a specific procedure:
- Measuring the reverberation time of the empty chamber: This involves measuring the reverberation without any sample.
- Testing with the sample: This involves measuring the reverberation with the sample. The sample must be at least 10 m².
- Calculating the coefficient: The sound absorption coefficient is derived from the difference in reverberation times between the empty chamber and the chamber with the sample.
Sound Absorption Coefficient – What is the Right One?
Determining the most reliable sound absorption coefficient depends on its intended use. The reverberation sound absorption coefficient provides averaged data suitable for room acoustics design, assuming sound will strike surfaces from all directions. The practical sound absorption coefficient offers slightly simplified data for similar applications. In contrast, the physical sound absorption coefficient, measured with an impedance tube at a 0-degree incidence angle, is suitable for designing enclosures. The weighted sound absorption factor is useful for classifying building elements based on their sound absorption capabilities.
How to Optimize the Sound Absorption Coefficient?
Creating a room that perfectly absorbs sound across the entire frequency spectrum is challenging and usually impractical outside specialized environments like anechoic chambers. In typical scenarios, the absorption coefficient is optimized for specific noise spectra relevant to the space. This optimization involves selecting appropriate materials with varying quality, structure, and thickness to achieve the desired acoustic properties.
Sound Absorption Coefficient – Where to Test?
Testing the sound absorption coefficient should be conducted in accredited laboratories to ensure compliance with established standards. A prime example of such a facility is the Acoustic Research and Innovation Center (ARIC) in Wrocław, equipped with multiple reverberation and anechoic chambers, automated measurement equipment, and national and EU accreditations. Established by KFB Acoustics, ARIC advances acoustic technology capabilities in both industrial and environmental contexts.