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Active noise reduction system

Ciesielka W.

Archives of Acoustics

2007

Vol. 32, No. 2

205-213

In this article, active noise reduction system has been described. The ANR system was made on basis of finite impulse response filter and realised algorithms LMS or NLMS. The algorithms were implemented on the dSPACE card with floating-point processor TMS320C31. Researches were performed in the anechoic chamber and in the enclosure of dimension 4.4 x 3.05 x 3.2 m and reverberation time T=0.53 s. White noise filtered by third and octave filter with mid-band frequency 125 Hz was used for the experiments. The ANR system working in free field conditions (in the anechoic chamber) allowed to obtain the average acoustic pressure level reduction ranging from 9.1 to 24.1 dB for octave, and 14.7 to 23.1 dB for third octave. Measurements carried out in natural acoustics conditions in a selected room allowed to obtain the following values of average acoustic pressure level reduction: for octave from 2.2 to 14.2 dB, and for third octave from 6.4 to 19.8 dB. The result of experiments proved that the convergence time of NLMS algorithm was several times shorter than convergence time of LMS algorithm.

An adaptive, active noise reduction system in closed space

Ciesielka W., Gołaś A.

Archives of Acoustics

2006

Vol. 31, No. 2

179-192

In this article, an active noise reduction system has been described. The ANR system was made on the basis of an finite impulse response filter and realised by LMS or NLMS algorithms. Those algorithms were implemented on the dSPACE card with a floating-point processor TMS320C31. The researches were performed in an enclosure of dimensions 4.4, 3.05, 3.2m. White noise filtered by third and octave filters with mid-band frequency 125Hz were used for the experiments. The result of experiments was a reduction of the sound pressure level, meanly from 10 to 20dB for the natural sound field. The investigations performed revealed that the location of reference and error microphones in the acoustic system - in the room, influence significantly the efficiency of the ANR system working. The investigations performed in a selected room (volume V=41.6m3 and reverberation time T=0.53s) revealed that projected and built up system gives very good effects in the active noise reduction for random, white noises of selected ranges.

Active control of sound by means of digital equalizers

Ciesielka W., Gołaś A.

Archives of Acoustics

2006

Vol. 31, No. 1

89-97

The article describes single-channel digital systems, enabling active sound control according to the set criterion. Theoretical fundamentals of these systems are based on digital filter theory, using which the digital graphic, phase, inverse and adaptive equalizers have been designed and programmed. The described systems have been implemented into two cards with signal processors TMS320C25 and TMS320C31 made by Texas Instruments. The article presents mathematical models of the above mentioned equalizers and results of the experimental tests, which verify their performance.