The PSI Audio AVAA C20 is designed to absorb the standing modes between 15 and 150 Hz in a room. Above these frequencies, passive systems are effective. For best results, the AVAA should be installed in a room where medium and high frequencies have already been treated with passive systems. With frequencies below 150 Hz, each operating AVAA will have the same effect as a hole in the wall much larger than the dimensions of the AVAA.
The exact ratio will depend on the frequency and environment but typically range between 5 and 25. The graph hereunder shows the typical equivalent absorption area of an active AVAA over the frequency bandwidth it is designed to absorb.
How Does it Work
A microphone will measure the acoustic pressure in front of an acoustic resistance. The acoustic resistance is designed to let air through but reducing significantly the pressure.
Behind the acoustic resistance, a transducer membrane is driven to absorb the volume of air going through the acoustic resistance as well as ensuring a specific acoustic impedance in front of this acoustic resistance.
When in function, this acoustic impedance in front of the acoustic resistance is significantly lower than in ambient air and therefore acts as a pressure sink.
The acoustic impedance of the air is affected typically over a radius of 1 to 1.5 m around the AVAA. This explains how the AVAA can be more absorbent that its actual surface of perfect absorber.
It is designed to absorb frequencies between15 and 150 Hz and is most effective on room modes that are the result of multiple reflections.
Note: that an AVAA is approximately 0.2 m2 so an equivalent sound absorbing area of 4 m2 is 20 times the surface of the AVAA.