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Acoustics and acoustic devices
Published in Michael Talbot-Smith, Audio Engineer's Reference Book, 2012
ALEXANDER, M., A current-feedback audio power amplifier. Presented at: 88th Convention at Montreux, AES Preprint 2902 (March 1990) AMBLER, R., Tone-balance control, Wireless World, 76, 124–126 (1970) AMOS, S.W., Radio, TV and Audio Technical Reference Book, Newnes-Butterworth, London (1977). (See Chap. 14 by P.J. Baxandall) ATTWOOD, B.E., Design parameters important for the optimization of very-high-fidelity PMW (class D) audio amplifiers, JAES, 31, 842–853 (1983) BAXANDALL, P.J., Negative-feedback tone control, Wireless World, 58, 402–405 (1952) BAXANDALL, P.J., Noise in transistor circuits, Part 1, Wireless World, 74, 388–392 (1968a) BAXANDALL, P.J., Noise in transistor circuits, Part 2, Wireless World, 74, 454–459 (1968b). Note: in Fig. 9, middle p diagram, the current generator labelled 2qIc B/gm should p be 2qIc B/rb ,e gm
Class XD: Crossover Displacement
Published in Douglas Self, Audio Power Amplifier Design, 2013
Figure 18.8 shows THD vs frequency for a standard Blameless Class-B amplifier giving 30 W into 8 U. The distortion shown only emerges from the noise floor at 2 kHz, and is here wholly due to crossover artefacts; the bias is optimal and this is essentially as good as Class-B gets. The distortion only gets really clear of the noise floor at 10 kHz, so this frequency was used for all the THD/amplitude tests below. This frequency provides a demanding test for an audio power amplifier. In all these tests the measurement bandwidth was 80 kHz. This may filter out some ultrasonic harmonics, but is essential to reduce the noise bandwidth; it is also a standard setting on many distortion analysers.
Transformers
Published in Kevin Robinson, Practical Audio Electronics, 2020
Figure 14.8 illustrates this situation – Figure 14.8a shows a 386 audio power amplifier connected directly to a loudspeaker as it is intended to be used. In this configuration the circuit will operate as expected and sound will emerge from the loudspeaker in the normal fashion. In Figure 14.8b however the loudspeaker has been replaced with a piezo driver. There is nothing wrong with the circuit per se, but the piezo will produce a very weak signal if any at all. There simply isn’t enough voltage available to get the piezo to move very much.
Determination of the acoustical performance of multipurpose music classrooms
Published in Architectural Science Review, 2022
Ahmet Aslan, Akın Oktav, Buket Metin
These parameters were measured across six octave bands, ranging from 125 Hz to 4000 Hz. The sound source and the receiver positions were determined according to OC I and OC II. Seven receivers (R1 – R7) were spread out where the student desks are located, with one source (S) placed in front of the whiteboard. The positions of the source and receivers are shown in Figures 6–8. The setup used in the measurement study includes: a dodecahedron omni-directional loudspeaker, two Behringer ECM 8000 microphones, an audio power amplifier, a Focusrite Scarlet 2i2 external audio interface, a laptop to employ Odeon 16 Auditorium, and three tripod stabilizers for the loudspeaker and microphones (see Figure 5). One of measurement microphones (which are identical) was determined to be the reference microphone, with the other one used as a roving microphone. The reference microphone was consistently located at the R1 position to provide reference data, while the roving microphone was located at the R2 to R7 positions, accordingly. The temperature and relative humidity data were recorded during the measurements using a datalogger (Aslan 2020).
A review on fast-frequency pulse TIG welding technology
Published in Welding International, 2022
Zhenmin Wang, Ge Lu, Chunming Hu, Sanbao Lin, Xianghui Ren, Jianwen Wu, Jiyu Tian
Based on the coupling of DC power supply and fast-conversion ultrasonic pulse power supply, the research team from Beijing University of Aeronautics and Astronautics [22] proposed a double-pulse modulation called UDP-VPTIG, that is, superimposing ultrasonic square wave pulse (20–80 kHz) on the waveform of low-frequency variable polarity pulse current (0.1–10 Hz) with current greater than zero and fast current change rate. When this method is used for the welding of aluminium alloy plates, the welding process is stable and good welding quality can be obtained. The weld penetration can be accurately controlled by adjusting the current waveform parameters. On the one hand, the addition of ultrasonic pulse current can significantly enhance the thermal effect of welding arc, make the arc heat source more concentrated and increase the arc force; on the other hand, by accurately regulating the working waveform of double pulse modulation variable polarity current, the accurate control of arc energy distribution and thermal characteristics can be realized to ensure the stable combustion of welding arc and enhance penetration. However, at present, the control of the pulse current amplitude coupled to the welding arc by the dual-pulse-modulated super-audio power supply is not accurate and stable enough, and the super-audio pulse current amplitude is low, so the applicable process range is small.
A Low-Cost, Wide-Range, CCT-Tunable, Variable-Illuminance LED Lighting System
Published in LEUKOS, 2020
Rajib Malik, Kalyankumar Ray, Saswati Mazumdar
The Transistor-transistor logic (TTL) to 12-V level converter cum Metal-Oxide Semiconductor (MOS) gate driver is used to ensure proper turn-on and turn-off of the three series dimming P55NF06-type Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFETs). The level converter cum driver is implemented using an LM386 low-voltage audio power amplifier. The driver is shown in Fig. 6. The cost of this device is very low compared to any dedicated commercially available MOSFET driver IC. The gain of the amplifier is internally set to 20 to keep the number of external parts to a minimum. Figure 7 shows that when the MCU signal is high, the drain terminal of Q1 (MOSFET) is low, so the LED string will be on during the high MCU signal. Measured values of turn-on and turn-off delays of the driver are 1900 ns and 400 ns, respectively, which are very small compared to the time period of 4.1 ms of the PWM signal.