STOPPING SOUND FROM ESCAPING

STOPPING SOUND FROM ESCAPING

STOPPING SOUND FROM ESCAPING

February 25 2015

In acoustics, managing high frequencies is relatively easy compared to bass. High frequencies have less energy and the shorter wavelengths cause the waves to be directional. This means we can predict where high frequency sound will travel by looking at the dispersion pattern of the PA system’s horn and drawing vectors outward. By positioning acoustic panels on hard reflective surfaces, excessive echo and room ambiance is attenuated.

Managing bass in an altogether different matter: bass waves are long, powerful and omni-directional meaning that they go everywhere. This not only makes them more challenging to control inside the room, but containing them is difficult if not impossible. When attempting to control bass from escaping, the first thing to do is to reduce the bass inside the room using bass traps. This will improve the sound of the audio system by reducing hotspots. With less energy in the room to contain, creating barriers becomes a bit easier. The next stage is determining how the bass is escaping. Doors and windows are often a source. These are generally addressed by adding mass to or by adding a second set. In doing so, bass energy must cause the first set of doors to vibrate, which in turn must cause the second set to do the same before the sound can escape.

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By introducing an air space between the two, you are decoupling the energy. Herein lays the magic to containing sound.

With walls, the trick is to build a heavy inner wall and ‘float it’ in front of the outer wall. This is usually done using resilient channel whereby the inner gypsum wall is left to vibrate freely on top of the outer wall. The heavy mass requires lots of bass energy to set it in motion, introducing yet another level of thermo-dynamic energy transfer which results in less energy for the outer wall to contain. Ceiling tiles are also a ready conduit for sound to escape. Light weight tiles do not stop bass, it simply passes straight through which causes the floor above to vibrate. Adding a mass component such as found in Primacoustic Thunder Tiles will help a lot. The gypsum mass component employed in the Thunder Tiles is first set to vibrate before the sound can reach the upper floor, greatly attenuating the energy. The air space introduced by the drop ceiling naturally decouples the two surfaces and one again, sound is better contained.

It is important to note that bass when driven to extremes can cause the concrete substructure of a building to vibrate. Stopping this type of energy is practically impossible. When analyzing the problem frequencies, you may find that the beams are resonating at a certain frequency and shifting the bass using an EQ can sometimes help.

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