AES London 2011
Paper Session P8

P8 - Audio Equipment

Saturday, May 14, 09:00 — 12:30 (Room 4)

John Dawson

P8-1 Signal Level and Frequency Dependant Losses Inside Audio Signal Transformers and How to Prevent ThoseMenno van der Veen, ir. bureau Vanderveen - Zwolle, The Netherlands
In an earlier work (Convention Paper 7125) a model was presented that explains that low voltage level audio signals are extra weakened when they are fed through a transformer. This extra weakening is caused by the signal level and frequency dependent inductance of the transformer. Combining this extra weakening with the threshold of hearing curves, showed that noticeable loss of micro details occurs in the frequency band from 20 Hz to 1 kHz. This paper expands the previous work with measurements on several valve amplifiers, refines the model, and makes it applicable to macro signal levels close to saturation of the transformer. Methods are also given to minimize this extra weakening in transformers.
Convention Paper 8360 (Purchase now)

P8-2 Diaphonic Pump: A Sound-Activated Alternating to Static Pressure ConverterStephen D. Ambrose, Robert Schulein, Asius Technologies LLC - Longmont, CO, USA; Samuel Gido, Asius Technologies LLC - Longmont, CO, USA, University of Massachusetts, Amherst, MA, USA
This paper discusses the operating principles and basic construction of a diaphonic pump, which is a newly invented device for harvesting the energy inherent in sound waves and using it to pump air, thereby pressurizing a vessel. Although this device is of general utility, the embodiment discussed in this paper is used to harvest sound energy from the speaker (balanced armature transducer) of a personal listening device (headset or hearing aid), and use this as a power source to inflate a bubble in the listener’s ear, thereby creating an acoustic seal. The diaphonic pump utilizes a natural asymmetry in the flow pattern when fluid is alternatingly pushed and pulled, back and forth through a small orifice known as a “synthetic jet.” Sound waves provide the alternating flow pattern across the synthetic jet orifice. Prototype diaphonic pumps were built, which attach to a back volume of a balanced armature transducer and are small enough that the whole assembly, transducer, and pump, can fit in a human ear canal.
Convention Paper 8361 (Purchase now)

P8-3 Scanning the Magnetic Field of Electro-Dynamical TransducersWolfgang Klippel, University of Technology - Dresden Germany, Klippel GmbH, Dresden, Germany
The magnetic flux density in the magnetic gap and the geometry of the moving coil determine the force factor Bl, which is an important parameter of the electro-dynamical transducer. The paper presents a new measurement technique for scanning the flux density B(z, f) on a cylindrical surface within and outside the magnetic gap using a Hall sensor and robotics changing the position of the sensor versus vertical position z and angle f. The results derived from the scanning process reveal the real B field in the gap considering the fringe field and irregularities in the magnetization, which may initiate a rocking mode and rubbing of the voice coil at higher amplitudes. Using the geometry of the coil the static force factor Bl(x, i=0) can be calculated as a function of voice coil displacement x and compared with the dynamic force factor B(x,i) measured by a dynamic system identification techniques. Discrepancies between dynamic and static force factor characteristics are discussed and conclusions for loudspeaker design and manufacturing are derived.
Convention Paper 8362 (Purchase now)

P8-4 Comparison of Anemometric Probe and Tetrahedral Microphones for Sound Intensity MeasurementsGiulio Cengarle, Toni Mateos, Fundació Barcelona Media - Barcelona, Spain
The measurement of sound intensity requires the acquisition of sound pressure and acoustic velocity in a coincident position. Various transducer topologies can be used to measure the acoustic velocity directly or indirectly. In this paper three transducers are compared: a pressure-velocity anemometric probe and two tetrahedral B-Format microphones from different manufacturers. The comparison has been carried out in different fields, ranging from anechoic to diffuse, reverberant field conditions. The analysis and comparison is based on intensimetric quantities such as the radiation index and the sound intensity vector. Strengths and limitations of the various approaches are reported, to suggest the preferred applications for each transducer.
Convention Paper 8363 (Purchase now)

P8-5 Prediction of Perceived Width of Stereo Microphone SetupsHans Riekehof-Böhmer, HAW-Hamburg - Hamburg, Germany; Helmut Wittek, Schoeps Mikrofone - Karlsruhe, Germany
The diffuse-field correlation of the two signals generated by a stereophonic microphone setup has an effect on the perception of spatial width. A correlation meter is often used to measure the correlation coefficient. However, due to the frequency dependence of the correlation function, the correlation coefficient is not an appropriate value for predicting the perceived width when it comes to time-delay stereophony. By using the newly defined “Diffuse-Field-Image-Predictor” (DFI-Predictor) presented in this paper an attempt is made to reliably predict perceived width. Listening tests show that the DFI-Predictor is fairly suitable for this task. The aim of the study is to compare the spatial properties of different stereophonic microphone techniques by one calculated value.
Convention Paper 8364 (Purchase now)

P8-6 Synthesis of Polar Patterns as a Function of Frequency with a Twin Microphone: Audio Examples and Applications within the Creative Process of Music MixingMatthias Kock, Erich-Thienhaus-Institute - Detmold, Germany; Markus Kock, Leibniz Universität Hannover - Hannover, Germany; Malte Kob, Erich-Thienhaus-Institute - Detmold, Germany; Rainer Maillard, Emil-Berliner Studios - Berlin, Germany
The directivity of a twin microphone can be chosen by variable weighting of the two output signals. In addition, the polar pattern can be adjusted as a function of frequency when controlled with a VST Plug-in in a modern DAW environment. A number of recordings were performed in rooms with variable size and quality. Presets with beneficial frequency-dependent directivities are compared to settings with constant directivity. It is discussed to what extend recordings can be further improved using the plug-in.
Convention Paper 8365 (Purchase now)

P8-7 Digital Microphones—What’s it All About?John Willett, Circle Sound Services - Oxfordshire, UK
It’s now ten years since the first AES42 specification was published (AES42-2001) and the first AES42-compliant digital microphone came to the market. So this seems an opportune moment to look at AES42 digital microphones, their history, what they offer, the current market situation, and what the future may hold.
Convention Paper 8366 (Purchase now)

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