Abstract: Transducer arrangement for use as receivers in acoustic borehole measurements, in particular for the purpose of geological steering, stratigraphic imaging and control during drilling of deviated and horizontal wells, whereby transducer sensitivity is focused generally in radial directions normal to the drill string axis in close proximity to the drill bit (45). Two separate and substantially similar transducer elements are adapted to be located at substantially the same axial position along the drill string axis. The transducer elements having their output terminals interconnected with opposite polarities, so as to have a combined minimum response to incident acoustic waves and vibrations being identical at both transducer elements.

Abstract: A method for active noise reduction based on destructive interference of sound waves in order to reduce the energy in a sound field employs two omnidirectional microphones (M1, M2) provided in connection with a loudspeaker. The acoustic feedback of the microphones is eliminated by a closed loop consisting of the microphones and the loudspeaker. The loudspeaker used is an open loudspeaker with a dipole characteristic, thus causing one of the microphones to be more sensitive to the far field and thereby to the noise which has to be suppressed. The method is implemented by a device which comprises a digital signal processor (DSP) for processing the microphone signals and which transmits an output signal to the loudspeaker where the feedback component from the loudspeaker is substantially eliminated, while the output signal's phase and amplitude are adjusted in such a manner that an effective cancellation of the noise is obtained in an area around the loudspeaker's near field.