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Suppressing low-frequency standing waves

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What are low-frequency standing waves?

In small, enclosed spaces such as listening rooms, a standing wave relative to the dimensions of the room occurs in the lower frequencies. This standing wave can be the source of poor-sounding lower frequencies, a boomy sound field, and a sense of stagnation distinctive of smaller rooms. Conversely, because a forest embodies an unclosed space, lower frequencies are ideally crisp, and the space does not have a sense of narrowness. The Acoustic Grove System eliminates low-frequency standing waves in smaller rooms while emphasizing crispness for better quality in low-frequency sounds, enabling an open sound field similar to a forest grove.

Mitigation of standing waves using AGS

Conventional countermeasures against standing waves commonly include installing sound absorbers in the corners of a room. However, this method is problematic because it is not very effective against low frequencies and the middle and high frequencies are excessively absorbed, taking away from the luster and comfort of sound. With the AGS, these disadvantages are mitigated for a sound field with improved lower frequencies.
How the peaks and dips in sound pressure caused by standing waves are heard differ greatly depending on where the listener is, and even when the listener is in the same place, how the sound is heard will differ greatly depending on the frequency. For example, a sound field can be defined as poorly balanced when one pitch in the bass can be heard but another cannot. Below, we look at the effects of the AGS through the results of a model experiment.
The figures below show the improvements gained through AGS installation. In a cuboid room 7.1 m wide by 5.0 m high with "Sound source SP" used as the sound source, the sound pressure distribution (80 Hz) was measured both before installation of the AGS (left figure, with bare walls on four sides) and after installation (right figure, with the AGS installed on one wall) (scale model test results with room dimensions and frequencies converted to actual values). Comparing the situations before and after AGS installation (area indicated by the blue dashed line), the peaks and dips in sound pressure are seen to be greatly alleviated even with installation of the AGS on one side of the room.

Improvements in room reverberation -- Before installation
Improvements in room reverberation -- After installation
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