Comparison of low-frequency background noise cancellation systems for room acoustics

Low frequency background noise (below 200 Hz) is perceptible in many situations such as in room acoustics or industrials issues. Generate by numerous type of source (traffic noise, aircraft, industrial plants, electricity transformer,… ), this type of noise is under evaluate by regulations laws due to the used of the A-weighted decibel (dB(A)). In spite of that low frequency background noise can reach high levels which produce poor speech intelligibility and annoyance feeling. Unfortunately traditional acoustic treatments have little impact to decrease this kind of disturbance. New approaches have to be developed to give new efficient techniques in order to overcome the problem. Three noise cancellation systems dedicated to low frequencies are studied here. The first one is based on an electromechanical transducers loaded passively to get an optimal damping around the resonance frequency of the disposal. In the second system the passive load is substituted by an active control to enhance acoustic properties of device. The last strategy consists on a control of the first modal frequencies of a room to decrease the low frequency background noise level. This paper aims at presenting those three noise cancelation systems. Their advantages and drawbacks will also be discussed.