This master's thesis addresses the design and implementation of a multi-sensor feedback control system for loudspeaker regulation (MFB, Motional Feedback), based on a custom-designed printed circuit board. The system enables comparison of two types of membrane motion sensors — a MEMS accelerometer and a piezoelectric accelerometer — via physical switches that let the user select between conventional (non-MFB) loudspeaker operation and operation with either sensor in the feedback loop. The theoretical section presents the basic principles of MFB control, the origin of nonlinear distortion in electroacoustic transducers, and a comparison of the properties of MEMS and piezoelectric acceleration sensors. Several accelerometers were tested, from which the two most suitable were selected — the ADXL326 (MEMS) and the AB2065B-LW100-R (piezo) — for which a sensor circuit was designed and mounted directly on the speaker's voice coil. Based on sensor circuit measurements, a complete circuit was designed, comprising a power supply section, a preamplifier, separate control stages for the MEMS and piezo sensors, output filters, an output power stage, and current protection. The circuit was implemented on a four-layer printed circuit board and assembled into a finished device ready for use, including a transformer-based mains power supply and fuse-based current protection. Measurements showed that using the MFB system shifts the lower limit of the loudspeaker's frequency response downward (from 40 Hz to 25 Hz with the MEMS sensor, and to 30 Hz with the piezo sensor) and flattens the frequency response within the usable range. It also reduces THD by at least 15% and by up to 82%, with the greatest reduction occurring mainly at low frequencies and high output voltages. Owing to its constant response down to DC, the MEMS sensor achieved better results than the piezo sensor in flattening the frequency response, while the latter has the advantage of lower inherent noise.
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