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Audio amplifiers
Published in Charlie Cullen, Learn Audio Electronics with Arduino, 2020
Otto Zobel published a 1923 paper for Bell Labs on impedance balancing that proposed the idea of image impedance, which in broad terms aims to match the impedance of one side of a network (known as a port into a network) with the other. In audio, this Zobel network takes the form of what is also known as a Boucherot cell, named after the French Railway engineer who first proposed using a series resistor and capacitor (or multiple capacitors) to cancel out the reactive component of an inductive load. In the diagram, the Zobel network of a resistor and capacitor is added to balance the inductor resistor combination (in grey) that represents a loudspeaker. The impedance of a loudspeaker is effectively a combination of both a resistive and an inductive component (due to the voice coil in the loudspeaker). For this reason, the concept of a loudspeaker as an output impedance load (see Figure 7.36) is more complex than simply ensuring that the operational amplifier presents as low an impedance as possible, because the loudspeaker impedance will vary with frequency due to the presence of the inductive component. For reasons of brevity, inductors have not been discussed in detail in this book but the basic concept of an inductor is in many ways the opposite of a capacitor, where inductive reactance increases with frequency (Figure 7.49).
Sensors and interfacing
Published in Mike Tooley, Electronic Circuits, 2019
Before we go further, let’s consider a couple of examples that you will already be familiar with. A loudspeaker is a transducer that converts low-frequency electric current into audible sounds. A microphone, on the other hand, is a transducer that performs the reverse function, i.e. that of converting sound pressure variations into voltage or current. Loudspeakers and microphones can thus be considered as complementary transducers.
Electronic fundamentals
Published in David Wyatt, Mike Tooley, Aircraft Electrical and Electronic Systems, 2018
Transducers are devices that convert energy in the form of sound, light, heat, etc., into an equivalent electrical signal, or vice versa. Before we go further, let’s consider a couple of examples that you will already be familiar with. A loudspeaker is a transducer that converts low frequency electric current into audible sounds. A microphone, on the other hand, is a transducer that performs the reverse function, i.e. that of converting sound pressure variations into voltage or current.
Countermeasures to Replay Attacks: A Review
Published in IETE Technical Review, 2020
Madhusudan Singh, Debadatta Pati
In replay mechanism the major components are microphone, loudspeaker and amplifiers. They act as a system and change the signal characteristics passing through it. For example, the inclusion of reflection and reverberation noise while collection of speech through microphone, quantization noise during digital conversion and distortion during reproduction of speech from the loudspeaker. Tracing the device response in replay signals is a difficult task, because the type of microphone and loudspeaker used for reproduction of speech is unknown. For example, the speech samples can be reproduced through laptops or smart phones. These devices exhibit different characteristics. Furthermore, tracing the device characteristics becomes comparatively less relevant when replay attempts are made with similar devices as used for the spoof protective authentication system. Because, the authentication system may be equipped to handle the data channel artifacts. The example of such a scenario is the use of a smart phone to replay the pre-recorded speech samples in order to unlock another smart phone.
Efficient projection onto a low-dimensional ball
Published in Engineering Optimization, 2019
Paul D. Teal, Lakshmi Krishnan, Terence Betlehem
Experimental studies were performed using channels measured using a repeated linear frequency sweep in a room of dimension with L=3 loudspeakers, M=2 microphones, number of taps and and a sampling frequency of 44.1 kHz. The number of pre-filter coefficients is thus . The reverberation time () of the room was 245 ms. The separation between two adjacent loudspeakers was 24 cm and that between the two microphones was 12 cm. The average loudspeaker-to-microphone distance was 37 cm. Such an arrangement could be used for example to deliver sound independently to the two ears of a human listener. The pre-echo and early reflection regions of the shaped responses were set to 10 and 40 ms (Bradley and Sato 2003; Kuttruff 2009; Betlehem, Teal, and Hioka 2012). The diagonal weighting matrix was set to match the temporal masking limit (Fielder 2001; Kahrs and Brandenburg 2002). The results for this arrangement are typical, and the speed and performance do not show much variation even in very different acoustic environments.
Dielectric properties of the chitosan – spinel CoFe2O4 composites
Published in Phase Transitions, 2018
E. Markiewicz, K. Chybczyńska, A. Grząbka-Zasadzińska, S. Borysiak, J. Wolak, M. Matczak
Composites are the materials consisting of several components interconnected by physical forces (e.g. adhesion). The properties of composites differ from those of its individual components. The proper choice of components and the technology of their interconnection permit production of composite materials of properties desired for specific applications. Some composites have been known for several thousand years, e.g. the Ramesses army (c. 1327–1237 BCE) in ancient Egypt was equipped with the composite bows prepared from properly chosen plant fibers and glues. Because of the outstanding elastic properties these bows had considerably longer range in comparison with those used by the enemies (e.g. Hittites in the bottle of Kadesh, 1302 BCE) which were made of homogenous wooden bars. Nowadays, worldwide laboratories tend to search for environmentally friendly composites with distinctive dielectric and magnetic properties suitable for application in modern transducers, for instance a loudspeaker without a permanent magnet [1]. The traditional loudspeaker has a voice coil, fixed to the membrane, which is suspended in the magnetic field of a permanent magnet. The current applied to the coil drives the coil-membrane system to move in the air generating the acoustic wave. In the proposed loudspeaker prototype [1] a composite membrane plays the role of the permanent magnet resulting in a considerable reduction of dimensions and mass of the loudspeaker.