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Motor Vibration and Acoustic Noise
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
Today, active noise reduction techniques have been successfully adopted in many commercial applications such as active mufflers, passage cars, wind tunnel testing systems, noise-cancelling headphones, and noise control in air-conditioning ducts. As a typical example, noise-cancelling headphones have been invented to eliminate any low-frequency noise from the environment. A variety of antinoise headphones is shown in Figure 12.52. These headphones involve using one or more microphones and an electronic circuitry that uses the microphone signals to generate antinoise signals, thus the generated destructive interference cancels out the ambient noise.
Headphone Amplifiers
Published in Douglas Self, Small Signal Audio Design, 2020
The wide range of load impedances is accompanied by a wide range of sensitivity. Headphones of 600 Ω impedance require 10 times or more voltage to achieve the same sound pressure level (SPL) than do those of 30 Ω impedance, though there is much variation. The sensitivity of most of the headphones currently on the market is covered by a range of +110 to +130 dB SPL per volt. If a rather loud +110 dB SPL is taken as the maximum level required, voltages between 110 mV and 1.1 V will be needed. These are low voltages compared with the maximum of about 10 Vrms that can be obtained from standard ±17 V rails, and you may be thinking that it would be more efficient to run a headphone amplifier off much lower rails, such as ±5 V. While this is true, it is rarely done, as a) it is much easier to get low distortion with the standard rails and b) extra power supplies are expensive to provide.
The Impact of Technology on Mental Health
Published in Bahman Zohuri, Patrick J. McDaniel, Electrical Brain Stimulation for the Treatment of Neurological Disorders, 2019
Bahman Zohuri, Patrick J. McDaniel
For example, if the detected brain output is indicative of the onset of an undesirable brain process, such as the initial stage of a seizure, then the signal generated by the device and delivered to the brain would provide an in-phase, equal magnitude, but opposite sign in order to cancel that signal through destructive interference with the output signal. This superposition of an opposite sign signal is similar to the method of acoustic noise cancellation commonly used in active acoustic noise cancellation headphones. Accordingly, a unique feature of the inventions provided in this disclosure is the application of a “cancellation signal” within the brain region generating the undesirable output signal.
Analysis of the external acoustic meatus for ergonomic design: part I – measurement of the external acoustic meatus using casting, scanning and rapid estimation approaches
Published in Ergonomics, 2021
Hao Fan, Suihuai Yu, Mengcheng Wang, Mei Li, Jianjie Chu, Yishu Yan, Shuai Zhang, Dengkai Chen, Carisa Harris-Adamson
Ear-related wearables have become ubiquitous and have a profound impact on our lives by providing a mechanism for instant communication, entertainment, hearing protection and noise reduction. Based on the wearing position (head, auricle, external acoustic meatus) of ear-related wearables, most of them can be categorised into over-ear (i.e. headphones, headsets), in-ear (i.e. earphones, in-ear/in-canal hearing-aids, ear-plugs, canal ear-buds, canal caps) and behind-ear (i.e. bone conduction headphones, behind-ear hearing aids, sports earphones) categories (Fan et al. 2019). Numerous studies of the external ear and related wearables have provided a better understanding of the methods, results and applications for auricular measurements, shape and product categorisation, all of which are important for product development (Jung and Jung 2003; Liu 2008; Roebuck and Casali 2011; Roebuck 2013, 2015; Yu et al. 2015; Stavrakos and Ahmed-Kristensen 2016; Ji et al. 2018; Mououdi, Akbari, and Mohammadi Khoshoei 2018; Lee et al. 2018; Fan et al. 2019; Roebuck 2019; Wang et al. 2019; Ban and Jung 2020; Fu and Luximon 2020). However, there are relatively few studies that have focussed on the external acoustic meatus (EAM) even though it is an important element of the auditory apparatus and should be considered when designing in-ear wearable devices.
Analysis of the external acoustic meatus for ergonomic design: part II – anthropometric variations of the external acoustic meatus by sex, age and side in Chinese population
Published in Ergonomics, 2021
Hao Fan, Suihuai Yu, Mengcheng Wang, Mei Li, Xiao Zhao, Yihui Ren, Shuai Zhang, Dengkai Chen, Carisa Harris Adamson
The human external ear consists of the auricle and the external acoustic meatus (EAM) (Standring 2016). The EAM extends from the auricular concha to the tympanic membrane (Figure A1). Based on the wearing position (head, EAM, auricle) of the ear-related wearables, most of them can be categorised into over-ear (i.e. headphones, headsets), in-ear (i.e. earphones, in-ear/in-canal hearing-aids, ear-plugs, canal ear-buds, canal caps) and behind-ear (i.e. bone conduction headphones, behind-ear hearing aids, sports earphones) categories (Fan et al. 2019). The design forms of the wearables are based on the required functions of the device and utilise multiple measurements that characterise the shape of the external ear (Grewe et al. 2013). Over the past two decades, to accommodate the different types and the functions of the ear-related wearable devices, the number of the auricular measurements to characterise the shape of the ear has increased from 4 (Jung and Jung 2003) to 18 (Lee et al. 2018, Fan et al. 2019). The measurements, including almost the entire auricle and its positional relationship to the head, inform the ergonomic design of the over-ear headphones/headsets and behind-ear headphones.
In-ear earphone design-oriented pressure sensitivity evaluation on the external ear
Published in Ergonomics, 2022
Yan Yan, Yonghong Liu, Jiang Rui, Kexiang Liu, Yujia Du, Haining Wang
The ear, which includes the external, middle, and internal ears, is an important organ in the head. Specifically, the external ear comprises an auricle (or pinna) and an external acoustic meatus (external auditory canal) (Drake, Vogl, and Mitchell 2018). Ear-related wearables can be categorised into the following based on the location: over-ear (headphones and headsets), in-ear (earphones, in-ear/in-canal hearing aids, ear plugs, canal earbuds, and canal caps), and behind-ear (bone conduction headphones, behind-ear hearing aids, and sports earphones) (Fan et al. 2019). Additionally, in-ear earphones are commonly used for real-time communication, hearing enhancement, and noise reduction in entertainment or working scenarios. Recently, true wireless stereo in-ear earphone technology has developed rapidly. However, the increased wearing time and scenarios (including jogging and walking) have led to a greater need for a well-fit, low-pressure, and highly stable experience. Previous studies on ear-related wearables reported the sense of pressure as a vital indicator of comfort. Notably, four major aspects of earplug comfort are as follows: physical, functional, acoustic, and psychological (Doutres et al. 2020). Static mechanical pressure is also one of the main attributes of physical comfort. Similarly, the four main factors related to wearing comfort include comfort, pain, pressure, and fixation (Song et al. 2020). Studies on the comfort of wearables during sleep reported less preference for devices that occupy more space in the outer ear canal with rigid parts (Röddiger, Dinse, and Beigl 2020). The pressure between the hard part of the wearables and the ear canal causes discomfort. Furthermore, a sense of discomfort and pain is a warning signal of potential danger (Xiong et al. 2010). Moreover, high pressure between the earbuds and the ear also induces the balance and locomotion sensors on the skin to trigger discomfort or pain, mainly due to a poor fit between the body and the device (Lee et al. 2017; Doutres et al. 2020). Therefore, high pressure should not be applied to ear-related devices since the sense of pressure is an essential indicator of discomfort or pain.