A device to monitor vibration excursion of speakers is disclosed. The device primarily uses a vibration sensor attached to the speaker suspension (surround). The sensor is overmolded onto the spider of the speaker. Both the sensor transducer and the acoustic transducer can use the -ve terminal as ground while voltage output of the sensor is monitored from the sensor +ve terminal. The surround moves together with the voice coil, which may or may not be attached to a former. The vibration sensor can be made of a PVDF coated thin piezo sensor or can be made of a flex sensor. The strain induced when the sensor is deflected will generate a voltage (in the case of the PVDF coated piezo) or a change in resistance for the flex sensor. These are monitored by a control circuit that computes the excursion from either of these parameters.
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Seguin, Chad and Asfaw, Michael, "Excursion Sensing On The Surround Of An Acoustic Transducer", Technical Disclosure Commons, (December 19, 2016)