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The microphone systems employed by smart devices such as cellphones and tablets require case penetrations that leave them vulnerable to environmental damage. A structural sensor mounted on the back of the display screen can be employed to record audio by capturing the bending vibration signals induced in the display panel by an incident acoustic wave - enabling a functional microphone on a fully sealed device. Distributed piezoelectric sensing elements and low-noise accelerometers were bonded to the surfaces of several different panels and used to record acoustic speech signals. The quality of the recorded signals was assessed using the speech transmission index, and the recordings were transcribed to text using an automatic speech recognition system. Although the quality of the speech signals recorded by the piezoelectric sensors was reduced compared to the quality of speech recorded by the accelerometers, the word-error-rate of each transcription increased only by approximately 2% on average, suggesting that distributed piezoelectric sensors can be used as a low-cost surface microphone for smart devices that employ automatic speech recognition. A method of crosstalk cancellation was also implemented to enable the simultaneous recording and playback of audio signals by an array of piezoelectric elements and evaluated by the measured improvement in the recording’s signal-to-interference ratio.
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Audio-Source Rendering on Flat-Panel Loudspeakers with Non-Uniform Boundary Conditions
Devices from smartphones to televisions are beginning to employ dual purpose displays, where the display serves as both a video screen and a loudspeaker. In this paper we demonstrate a method to generate localized sound-radiating regions on a flat-panel display. An array of force actuators affixed to the back of the panel is driven by appropriately filtered audio signals so the total response of the panel due to the actuator array approximates a target spatial acceleration profile. The response of the panel to each actuator individually is initially measured via a laser vibrometer, and the required actuator filters for each source position are determined by an optimization procedure that minimizes the mean squared error between the reconstructed and targeted acceleration profiles. Since the single-actuator panel responses are determined empirically, the method does not require analytical or numerical models of the system’s modal response, and thus is well-suited to panels having the complex boundary conditions typical of television screens, mobile devices, and tablets. The method is demonstrated on two panels with differing boundary conditions. When integrated with display technology, the localized audio source rendering method may transform traditional displays into multimodal audio-visual interfaces by colocating localized audio sources and objects in the video stream.
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- Award ID(s):
- 2104758
- PAR ID:
- 10318141
- Date Published:
- Journal Name:
- 151st Convention of the Audio Engineering Society
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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