Where n is the well number (1, 2, 3, etc), N is a prime number that determines the total number of wells (7, 11,ġ3, etc), and λ is the wavelength of the design frequency. To calculate the well depths of such a diffuser, the equation 9 is used: So, the mathematical relationship between reflectivity and absorption is:Įquation 9: Well depth calculation for a Schröder diffuser Absorption can be thought of as simply a lack Look at this the other wayĪround-if only 2% is absorbed, then 98% of the sound is reflected. If you look at the absorption value at 250Hz, you will see that it is 0.02, or 2%. The absorbency only becomes appreciable at 16KHz. Table 1: Absorption values for thin carpet with no underlay on concreteĪs you can see, this particular thin carpet is pretty much useless for absorbing sound below 2KHz, and only More detailed absorbency figures are sometimes quotes across 9 octave bands.įor instance, thin carpet with no underlay on a concrete floor has the following absorbency values: The columns It is standard practice to quote absorbency values for at least six standard frequencies, each being an octave Important that you also quote for which frequency the absorption value is relevant. Therefore, when quoting the absorbency of a material, it is very It must also be understood that a particular material may be a very good absorber of high frequency sounds, butĪlso a very poor absorber of low frequency sounds. Similarly, if a wall ten square metres in area absorbs 35% of the incident sound energy, then the entire wall hasĪ total absorption of 3.5 Metric Sabins. If one square metre of a material absorbs 28% of the incident sound energy, then it is said to have an absorption (If the word “Metric” is omitted, then it is assumed that the area is one square foot). This would be described has having 1 Metric Sabin ofĪbsorbency. So now imagine our window has an area of one square metre. The open window can be thought of as a perfect absorber because any sound that passes through it never and at that point on the wall, you cannot here any reflections at all. Stand facing an open window, you can only hear coming from the room behind you. Room you can hear sound coming from all directions as it bounces off the walls, floor and ceiling. In order to understand absorbency, imagine you are in a room in which music is playing. Material absorbs at a particular frequency. The absorption of a material is measured in (Metric) Sabins and represents the proportion of sound energy that a Not only do different surfaces absorb sounds to different degrees theĪbsorbency of a surface varies with frequency. The science of architectural acoustics pays particular attention to a property that every substance possesses to
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