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It is unclear whether the brain handles auditory cues similarly to visual cues for balance. We investigated the influence of headphones and loudspeaker reproduction of sounds on dynamic balance performance when an individual is facing a cognitive challenge. Twenty participants (16 females, aged 19-36) were asked to avoid a ball according to a specific visual rule. Visuals were projected from the HTC Vive head-mounted display in an acoustically controlled space. We varied the environment by adding congruent sounds (sounds coincide with the visual rule) or incongruent sounds (sounds may or may not coincide with the visual rule) as well as creating a multimodal (visual and congruent sounds) vs. unimodal (visual or congruent sounds only) display of stimuli. Sounds were played over headphones or loudspeakers. We quantified reaction time (RT) and accuracy (choosing the correct direction to move) by capturing the head movement. We found that in the absence of sounds, RT was slower with headphones compared to loudspeakers, but the introduction of either congruent or incongruent sounds resulted in faster movements with headphones such that RT was no longer different between apparatus. Participants used congruent sounds to improve accuracy but disregarded incongruent sounds. This suggests that selective attention may explain how sounds are incorporated into dynamic balance performance in healthy young adults. Participants leveraged sounds played over loudspeakers, but not over headphones, to enhance accuracy in a unimodal dark environment. This may be explained by the natural listening conditions created by loudspeakers where sounds may be perceived as externalized.

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A wearable Braille-to-speech translation system is of great importance for providing auditory feedback in assisting blind people and people with speech impairment. However, previous reported Braille-to-speech translation systems still need to be improved in terms of comfortability or integration. Here, a Braille-to-speech translation system that uses dual-functional electrostatic transducers which are made of fabric-based materials and can be integrated into textiles is reported. Based on electrostatic induction, the electrostatic transducer can either serve as a tactile sensor or a loudspeaker with the same design. The proposed electrostatic transducers have excellent output performances, mechanical robustness, and working stability. By combining the devices with machine learning algorithms, it is possible to translate the Braille alphabet and 40 commonly used words (extensible) into speech with an accuracy of 99.09% and 97.08%, respectively. This work demonstrates a new approach for further developments of advanced assistive technology toward improving the lives of disabled people.

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Film-type shape-configurable speakers with tunable sound directivity are in high demand for wearable electronics. Flexible, thin thermoacoustic (TA) loudspeakers-which are free from bulky vibrating diaphragms-show promise in this regard. However, configuring thin TA loudspeakers into arbitrary shapes is challenging because of their low sound pressure level (SPL) under mechanical deformations and low conformability to other surfaces. By carefully controlling the heat capacity per unit area and thermal effusivity of an MXene conductor and substrates, respectively, it fabricates an ultrathin MXene-based TA loudspeaker exhibiting high SPL output (74.5 dB at 15 kHz) and stable sound performance for 14 days. Loudspeakers with the parylene substrate, whose thickness is less than the thermal penetration depth, generated bidirectional and deformation-independent sound in bent, twisted, cylindrical, and stretched-kirigami configurations. Furthermore, it constructs parabolic and spherical versions of ultrathin, large-area (20 cm × 20 cm) MXene-based TA loudspeakers, which display sound-focusing and 3D omnidirectional-sound-generating attributes, respectively.

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Facilitated by microelectromechanical systems (MEMS) technology, MEMS speakers or microspeakers have been rapidly developed during the past decade to meet the requirements of the flourishing audio market. With advantages of a small footprint, low cost, and easy assembly, MEMS speakers are drawing extensive attention for potential applications in hearing instruments, portable electronics, and the Internet of Things (IoT). MEMS speakers based on different transduction mechanisms, including piezoelectric, electrodynamic, electrostatic, and thermoacoustic actuation, have been developed and significant progresses have been made in commercialization in the last few years. In this article, the principle and modeling of each MEMS speaker type is briefly introduced first. Then, the development of MEMS speakers is reviewed with key specifications of state-of-the-art MEMS speakers summarized. The advantages and challenges of all four types of MEMS speakers are compared and discussed. New approaches to improve sound pressure levels (SPLs) of MEMS speakers are also proposed. Finally, the remaining challenges and outlook of MEMS speakers are given.

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A flexible fiber acoustic transducer is created by designing a parallel configuration of a Rubidium iron boron (NdFeB) magnet fiber and an aluminum fiber. The former provides a stable magnet field, while the latter vibrates to phonate upon applying alternating current or generates alternating voltage in the sound field. This single device exhibits dual functions as a loudspeaker or a microphone. As a fiber loudspeaker, it can generate 40-60 dB of audible (20 Hz-20 kHz) and directional sounds which can be used for blind navigation and controllable sound field distribution. The fiber acoustic transducer functions as a microphone when external sound waves force the aluminum fiber to vibrate. After the fiber microphones are woven into several different positions of a piece of clothing, the sound source can be accurately located based on the time differences reaching different microphones. This wearable fiber acoustic transducer is promising to be used to quickly search people in trouble during emergency rescue activities such as earthquakes or fires.

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The trend to a world with ubiquitous electronics has the need for novel concepts for sensors and actuators that are lightweight, flexible, low-cost, and also sustainable. Piezoelectric transducers on the basis of functional polymers can meet these expectations. In this work, a novel concept for paper-embedded large-area piezoelectric devices realized solely by means of roll-to-roll (R2R) mass printing and post printing technologies including inline poling are introduced. The device set-up, as well as the process technology, offers the great opportunity for a cost-efficient and environmentally friendly mass production of thin and flexible organic large-area piezoelectric devices. As the functional layers are embedded into paper by the hot lamination of two poly(vinylidene fluoride-co-trifluoroethylene) P(VDF-TrFE) layers, the printed electronics is protected and invisible. The paper gives insights to the R2R printing of a 500 m long web including R2R post printing processes and electrical and acoustic inline characterization. Fully R2R processed devices show a high remnant polarization of up to 78 mC m-2 and can be realized with high yield of >90%. Finally, a 360° surround-sound installation realized with a 387 cm long paper web consisting of 56 piezoelectric speakers including wiring is presented.

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Thermoacoustic (TA) loudspeakers have garnered significant attention in recent times as a novel film speaker that utilizes temperature oscillation to vibrate the surrounding air. Conventional film-type TA loudspeakers are known to experience problems when external environments damage their conductive networks, causing them to malfunction. Therefore, introducing self-healing polymers in TA loudspeakers could be an effective way to restore the surface damage of conductive networks. In this study, we present transparent, flexible, and self-healable TA loudspeakers based on silver nanowire (AgNW)-poly(urethane-hindered urea) (PUHU) conductive electrodes. Our self-healable AgNW/PUHU electrodes exhibit significant self-healing for repairing the surface damages that are caused due to the dynamic reconstruction of reversible bulky urea bonds in PUHU. The fabricated self-healable TA loudspeakers generate a sound pressure level of 61 dB at 10 kHz frequency (alternating current (AC) 7 V/direct current (DC) 1 V). In particular, the TA speakers are able to recover the original sound after healing the surface damages of electrodes at 95 °C and 80% relative humidity within 5 min. We believe that the technique proposed in this study provides a robust and powerful platform for the fabrication of transparent and flexible TA loudspeakers with excellent self-healing, which can be applied in flexible and wearable acoustic electronics.

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The growing importance of human-machine interfaces and the rapid expansion of the internet of things (IoT) have inspired the integration of displays with sound generation systems to afford stretchable sound-in-display devices and thus establish human-to-machine connections via auditory system visualization. Herein, the synchronized generation of sound and color is demonstrated for a stretchable sound-in-display device with electrodes of strain-insensitive silver nanowires (AgNWs) and emissive layers of field-induced inorganic electroluminescent (EL) phosphors. In this device, EL phosphors embedded in a dielectric elastomer actuator (DEA) emit light under alternating-current bias, while audible sound waves are simultaneously generated via DEA actuation along with input sound signals. The electroluminescence and sound-generation performances of the fabricated device are highly robust and reliable, being insensitive to stretch-release cycling because of the presence of the AgNW stretchable electrodes. The presented principle of integrating light emission and acoustic systems in a single stretchable device can be further expanded to realize sound-in-display electronics for IoT and human-machine interface applications.