ACTIVE CONTROL OF LOW-FREQUENCY SOUND-TRANSMISSION BETWEEN ROOMS

The sound insulation properties of many structures mounted between adjacent rooms are known to be poor at low frequencies. The feasibility of using acoustic secondary sources in either the source room, or in the receiving room, to actively control the sound transmitted from one room to the other via a common panel has been investigated. A theoretical formulation for such low-frequency sound transmission was first developed. The effects of three different active control strategies were then investigated, using computer simulations with a pure-tone primary source, for a number of different room and panel arrangements. The first strategy involved minimizing the total acoustic potential energy in the source room using a secondary source in the source room. It was found that this could cause increases in the acoustic energy transmitted into the receiving room at some excitation frequencies. Second, the total acoustic potential energy in the receiving room was minimized using a secondary source in the receiving room. This strategy generally produced rather small reductions of sound energy in the receiving room. Finally, the approach of minimizing the total acoustic potential energy in the receiving room using a secondary acoustic source in the source room was investigated. This turned out to be the most successful strategy, giving significant reductions in transmitted sound energy, particularly for excitation frequencies at which only a few acoustic modes of the source room or structural modes of the panel were excited. These reductions in transmitted sound energy may, however, be accompanied by increases in the sound energy in the source room.