Reflection, Absorption, Diffusion - Wilson Benesch Precision Series User Manual

2.3 Reflection, Absorption, Diffusion

The upper-range of frequencies is generally affected more by room contents than room shape. The surfaces and how they reflect, absorb
or diffuse acoustic energy will tend to describe the 'sound' of a room. As is the case with all forms of energy, acoustic energy cannot
be destroyed it can only be converted or reflected. The shape, thickness and material type of a surface will determine how the sound is
reflected, how much of it is reflected and also how much is absorbed and converted into heat or kinetic energy.
Depending on the frequencies in question, the thickness, density and material of the surface or boundary, some energy may pass through
entirely. This behaviour is commonly observed in the lower range of frequencies, being comprised of larger wavelengths that can pass
through wall or ceiling boundaries and into an adjacent room, while the upper frequencies are either absorbed or reflected back inside
the listening room.
Diffusion occurs when acoustic energy is reflected by a surface and dispersed in a random and/or disordered fashion. Usually, diffusion
will occur when the acoustic energy meets a non-uniform or uneven surface. A tightly packed bookshelf with books of different sizes and
profiles is one example of a commonly found listening room boundary which can result in diffusion of the upper frequencies.
Diffusion of sound energy at key areas of the listening room is often less damaging to system accuracy and therefore preferable to
orderly reflection. In the case of reflection, the quantity of indirect sound reaching the listening position will be greater and therefore
more influential. This mixing of indirect and direct sound at the listening position can result in audible inaccuracies and artefacts.
It should be appreciated that sound waves behave in much the same way as light waves or 'rays'. To imagine the loudspeaker driver as a
floodlight can be helpful in determining which areas of the listening space are critical to the performance and accuracy of the system. The
key "first points of reflection" can be roughly identified by having an assistant hold a mirror on each side wall while you are positioned in
the listening chair. Once the speaker drivers can be seen in the mirror from the listening position the impact of this identified area should
be considered in light of the above basic principles. By the same token, the first reflection point on the ceiling can also be considered for
its influence as the first point of reflection.
Although many listening rooms are unsuitable for professional acoustic treatment products due to their dual role as a living and listening
space, it can still be possible to make small but appreciable improvements by rearranging furniture, system components and of course
the listening position. Consider the changeability of rooms; if the room is dressed with heavy curtains simply changing the curtains
position can alter the balance of the system. It is the goal that is the guide and the owner is the pivot in this subtle balancing act.
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