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Preventing adverse effects of intense reflected sound waves

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Mechanisms for realizing natural reverberations

The figures below show a computer simulation of sound being reflected off two types of walls. The figure on the left shows specular reflection by a hard, flat wall. The figure on the right shows "natural reverberation" achieved through the use of the Acoustic Grove System. With specular reflection, a single reflected sound (reflection) with strong levels arrives immediately following the direct sound (direct) from the speaker. In small spaces such as studios or listening rooms, the interval between the direct sound and the reflected sound is generally short, possibly resulting in "specular characteristics" where the fusion of the direct and reflected sound can be heard. In larger spaces such as a concert hall, the interval between the direct sound and the reflected sound will be longer, resulting in acoustic obstacles such as flutter echo.
Because such phenomena hinder the proper evaluation of the original sound source, a sound-absorbing sound field capable of excluding as much reflected sound as possible is required at the location of the sound creation. Spaces treated with sound absorption are often referred to as "dead" sound fields. Meanwhile, echoing spaces are referred to as "live" sound fields. However, when sound absorption designed to eliminate reflected sounds becomes excessive, the sound field may tend to be a rather boring place for enjoying sound.
This is where reflections caused by the AGS shine. The incident sound is scattered by the AGS without causing specular reflection where the direct sound and wavefront are aligned, resulting in only a small amount of reflected sound with no sudden loss in energy from sound absorption, allowing for temporal and spatial dispersion. This scattering phenomenon of the sound waves creates "natural clear sound".

Reflected sound with flat walls
Scattered reflected sound with AGS

Measuring rich sound

To verify the computer simulation data, reflection characteristics where also measured using an actual AGS setup (shown in the photograph). The figure below shows the time-based changes of actual measured reflection energy with hard, flat walls and with the AGS.
With a flat wall (top figure), reflected sound at high levels can be seen due to specular reflection, just as in the simulation. As described above, sound quality is adversely affected because there is little level difference between the reflected sound and the direct sound. Moreover, sound reflected on the wall surface can cause multiple flutter echoes to be generated between the wall and the cabinet where the sound source speaker is placed. The fact that a cabinet measuring only 20 cm × 40 cm can reflect this much sound might surprise some readers.
With the AGS (bottom figure), however, not one high-level reflected sound is heard. The figure illustrates how the reflected sound energy is far lower than the direct sound, and this reflected sound is dispersed over time for a gentle decay. Such characteristics enable a "natural sound" with no loss in the clarity of the direct sound and no generation of flutter echoes.

Actual measurement in an anechoic room (flat wall)
Actual measurement in an anechoic room (AGS)
Anechoic room experiment results
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