AES San Francisco 2010
Poster Session P13

P13 - Audio Equipment and Measurement

Friday, November 5, 2:30 pm — 4:00 pm (Room 226)

P13-1 Neutral-Point Oscillation Control Based on a New Audio Space Vector Modulation (A-SVM) for DCI-NPC Power AmplifiersVicent Sala, Luis Romeral, G. Ruiz, UPC-Universitat Politecnica de Catalunya - Terrassa, Spain
In this paper the oscillation or flotation in the DC-BUS neutral point in the DCI-NPC (Diode Clamped Inverter – Neutral Point Clamped) amplifiers is presented as one of the most important distortion sources. This perturbation is characterized and studied, as well as its causes and distorting effects. It also presents two techniques of vector modulation for audio. The intelligent use of these techniques in the process of vector modulation allows the redistribution of the charge of the two capacitors in the DC-BUS, allowing the control of the voltage in the neutral point of the DC-BUS, and therefore, the cancellation of the flotation and its distorting effects. Experimental and simulation results that verify these strategies are presented.
Convention Paper 8227 (Purchase now)

P13-2 Vacuum Tube Amplifiers Using Electronic DC TransformersTheeraphat Poomalee, Kamon Jirasereeamornkul, King Mongkut’s University of Technology Thonburi - Tung-kru, Bangkok Thailand; Marian K. Kazimierczuk, Wright State University - Dayton, OH, USA
This paper proposes a method to synthesis vacuum-tube audio amplifiers using the electronic DC transformers to replace the traditional audio-frequency output transformers usually used in the output stage of the amplifier. The proposed amplifiers can achieve the frequency response from DC-100 kHz if the DC transformers operated at 500 kHz switching frequency and interleave technique are used. The principle of operation, DC model, and various examples are given.
Convention Paper 8228 (Purchase now)

P13-3 The Single Stereo Display and Stereo VU MetersMichael D. Callaghan, Radio Station KIIS-FM - Los Angeles, CA, USA
This paper describes the use of a single row of bi-color indicators to replace and overcome the deficiencies of the typical pair of meters used to show left and right signal levels in stereo applications. By using bi-color elements, a total of three colors are actually obtained; a single color when the left channel is driven, a single color when the right channel is driven, and a mixture of the two when both channels are driven. Watching the row of indicators during program operation will indicate three different amplitudes; the left channel volume, the right channel volume, and the difference between the two of them. These amplitudes are immediately obvious and very easy to interpret.
Convention Paper 8229 (Purchase now)

P13-4 Frequency Characteristics Measurements of Cylindrical Record Player by the Pulse-Train MethodTeruo Muraoka, Takahiro Miura, Tohru Ifukube, The University of Tokyo - Tokyo, Japan
The authors have been engaged in the research of restoration of seriously damaged audio signals employing Generalized Harmonic Analysis (GHA). In this research it is important to know frequency characteristics of sound reproducing equipment to obtain clear sound with proper tonal equalization. The authors previously measured frequency characteristics of several acoustic 78 rpm shellac-record players utilizing the Pulse-Train Method, and successively measured cylindrical record players with same method recently. Frequency characteristics of phonograph record players were measured using frequency test records conventionally, however it is impossible to obtain shellac or cylindrical test records any more. Therefore the authors employed the Pulse-Train Method, which was originally developed for the measurements of phonograph cartridges and cutter heads in 1970s. For the measurement this time, the authors first made a cylindrical record curved a silent sound groove and curved an additional groove perpendicular to the sound groove on the cylinder surface. Pulse-train response was obtained by reproducing the cylindrical record using object record players and reference electric record player. Frequency characteristics of object record players were analyzed applying DFT to measured Pulse-Train waveforms.
Convention Paper 8230 (Purchase now)

P13-5 Seeing Sound: Sound Sensor Array with Optical OutputsCharles Seagrave, Seagrave Instruments - San Rafael, CA, USA; Eric Benjamin, Consultant - Pacifica, CA, USA
Characterization of acoustic spaces frequently involves taking SPL measurements at numerous locations within the space. Such measurements typically require relocation of the measurement apparatus or multiple microphones wired to a multiplexer. This approach can be time consuming, especially if it must be repeated after changes in loudspeaker location or acoustical treatments of other modifications. This paper presents methods of visualizing both standing waves in rooms and loudspeaker coverage uniformity in outdoor venues, using an array of sound sensors with optical (visible light) output. This new approach allows for rapid visual observation of sound fields, and simultaneous SPL data collection from multiple positions.
Convention Paper 8231 (Purchase now)

P13-6 Effects of Oversampling on SNR Using Swept-Sine AnalysisChristopher Bennett, Daniel Harris, Adam Tankanow, Ryan Twilley, Oygo Sound, LLC - Miami, FL, USA
The swept-sine technique is an alternative method to acquire impulse response measurements and distortion component responses. Swept-sine analysis has been under recent investigation for its use in auditory applications. In this paper the researchers seek to show that an improvement in signal-to-noise ratio (SNR) can be achieved by applying oversampling while utilizing swept-sine analysis. Oversampling does not give an improvement in SNR in traditional click impulse response methods; however, due to the noise shaping properties of the post-processing involved in swept-sine analysis, the noise floor can be reduced.
Convention Paper 8232 (Purchase now)

P13-7 Rapid In-Place Measurements of Multichannel VenuesJohn Vanderkooy, University of Waterloo - Waterloo, Ontario, Canada
It is often useful to have transfer-function measurements of large venues with an audience present. This precludes multiple chirps or other long-duration signals from being used. This paper studies the use of simultaneous, multiple “orthogonal” maximum-length sequences applied to the loudspeakers, captured by a number of microphones at selected listening positions. Such MLS signals last only a few seconds and are noise-like, being minimally disruptive to an audience, yet they allow full transfer-function system identification between each loudspeaker and microphone. The main detractor of the method is that the effective noise level is high. This paper studies implementation issues and assesses the S/N of such measurements. It turns out that exciting each loudspeaker separately is usually better than simultaneous excitation, except in special circumstances. An example is shown for the simultaneous measurement of two loudspeakers in a room with two microphones.
Convention Paper 8233 (Purchase now)

P13-8 Ground Loops: The Rest of the StoryBill Whitlock, Jensen Transformers, Inc. - Chatsworth, CA, USA; Jamie Fox, The Engineering Enterprise - Alameda, CA, USA
The mechanisms that enable so-called ground loops to cause well-known hum, buzz, and other audio system noise problems are well known. But what causes power-line related currents to flow in signal cables in the first place? This paper explains how magnetic induction in ordinary premises AC wiring creates the small voltage differences normally found among system ground connections, even if “isolated” or “technical” grounding is used. The theoretical basis is explored, experimental data shown, and an actual case history related. Little has been written about this “elephant in the room” topic in engineering literature and apparently none in the context of audio or video systems. It is shown that simply twisting L-N pairs in the premises wiring can profoundly reduce system noise problems.
Convention Paper 8234 (Purchase now)

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