One dimensional study of a module for active/passive control of both absorption and transmission

Hybrid active/passive absorbers have proven to be efficient over a large frequency range. The next step consists in building up a system which can exhibit good absorption and insulation properties. To simulate such hybrid cell, active and passive behaviors of an electroacoustic loudspeaker have been modelized by using a one-dimensional approach. The rear acoustic load at the back of the membrane has been taken into account to obtain a reliable model. The proposed model has been validated with measurements performed in a 7 cm diameter tube. Then, a hybrid cell composed of a porous plate and a small thickness loudspeaker has been designed and numerically tested. It is shown that, when driving the loudspeaker for total absorption, the transmission losses are suppressed at lower frequencies. To overcome this problem, a dual actuator cell is designed to deal with both absorption and transmission. Simulations shows that this solution can lead to good results. It is also shown that interaction of the loudspeakers can be significantly reduced by using directive sources, thus lowering supplying voltages and condition number of the matrix inversion required by the control process.