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Session H Sunday, May 13 13:30 - 18:00 hr Room C/D


Chair: David Josephson, Josephson Engineering, San Jose, CA, USA

13:30 hr H-1
The 48-Volt Phantom Menace
Gary Hebert & Frank Thomas
THAT Corporation, Milford, MA, USA

The authors encountered anecdotal evidence suggesting that field failures of existing line driver and microphone preamplifier integrated circuits (ICs) were correlated with accidental connections between line outputs and microphone inputs with phantom power applied. Analysis showed that the most probable mechanism was large currents flowing as a result of rapid discharge of the high-valued ac-coupling capacitors. Commonly used protection schemes are measured, analyzed, and shown to be lacking. More robust schemes that address these shortcomings are presented. It is concluded that the small additional cost of these more robust protection schemes is likely outweighed by the reduction in field failures and their associated repair cost.
Paper 5335

14:00 hr H-2
The Quick Reference Guide to Multichannel Microphone Arrays - Part I: using Cardioid Microphones
Michael Williams (1) & Guillaume Le Du (2)
(1) Sounds of Scotland, Le Perreux sur Marne, France
(2) Radio France, Paris, France

No one microphone array is able to fulfil the needs of the sound engineer in all the different sound recording environments he encounters. This paper presents over 220 Multichannel Microphone Arrays using cardioid microphones, and describes their particular characteristics with respect to front-triplet, lateral-pair and back-pair coverage together with the specific segment offset values when required for Critical Linking. Arrays have been chosen so as to assist the sound engineer in his search for the optimum microphone array for a given recording situation.
Paper 5336

14:30 hr H-3
Improved Microphone Array Configurations for Auralization of Sound Fields by Wave Field Synthesis
Edo Hulsebos, Emmanuelle Bourdillat & Diemer de Vries
Technical University Delft, Delft, The Netherlands

In order to correctly reproduce (íauralizeí) the acoustic wave field in a hall through a Wave Field Synthesis (WFS) system, impulse responses are nowadays measured along arrays of microphone positions. In this paper three array configurations are considered: the linear array, the cross array and the circular array. The linear and cross array configurations both have strong limitations, most of which can be avoided by using circular arrays. In this paper auralization techniques are explained for all three types of arrays. For the circular array configuration the connection between circular holophony, high-order incoming and outgoing ambisonics and plane wave decomposition for a sound field will be established and used as tools for auralization.
Paper 5337

15:00 hr H-4
Omnis and Spheres - Revisited
Martin Schneider
Georg Neumann, Berlin, Germany

The geometry of the microphone surrounding a transducer capsule has a large influence on the acoustical behavior of the transducer as a whole. Therefore, only 4 microphone design principles are in common use today: with mostly free-standing capsules; with cylindrical housings; embedded in large boundary layers; or with spherical housings. Especially for omnidirectional pressure transducers, the spherical housing can be applied, yielding positive results on frequency response and polar pattern. Spherical housings have been investigated, and introduced to microphone design some 50 years ago. An overview of the historical development, and their applications shall be presented as well, leading to the current embodiments of this principle.
Paper 5338

15:30 hr H-5
Optimization of the Diffuse Field Performance of a Miniature Highly Directional Array Microphone
Wim Soede (1) & Robert Schulein (2)
ARDEA Development and Electronics, Leiden, The Netherlands
Etymotic Research, Elk Grove Village, IL, USA

The focus of this development effort has been the design of a small highly directional array microphone. Such a design is valuable for applications where the directivity of 1st order microphones is too low and the physical size of traditional shotgun or parabolic microphones prohibits their use. Application examples include hearing aids, automotive mobile phones, and interview situations with less visibility of the microphones.
Paper 5339

16:00 hr H-6
Proximity Effect and Space Characteristics of Microphones
Emil Milanov & Elena Milanova
Consultants, Sofia, Bulgaria

In this article are described the polar patterns of electro-dynamic microphones with two acoustical entrances. By definition the polar pattern is a ration between the microphone sensitivity when thita angle varies in related to the sensitivity when thita is 0 degrees when the frequency and the sound pressure are constant. It is well known that the reason for the proximity effect is the change of the wave front from a plane to a sphere when the distance to the sound source decreases. In this article we will define the relations of the polar pattern in a wave front with a sphere and plane form.
Paper 5340

16:30 hr H-7
The Digitally Interfaced Microphone - The Last Step to a Purely Digital Front-to-End Audio Signal Transmission and Processing Chain
Stephan Peus & Otmar Kern
Georg Neumann, Berlin, Germany

With the introduction of the AES 42 standard, defining the digital interfacing of microphones, and the availability of the first digital microphones, the last obstacle is taken in the complete digitization of the audio signal transmission chain. The basic differences and problem definitions in comparison to analog microphone technique are presented. Digital microphones can contain remote controllable functions, which were so far available only in the following signal processing, e.g. in a mixing console. Advantages and possibilities of using the new technique are shown based on an example.
Printed Paper not available

17:00 hr H-8
Suppression of Switch Mode Power Supply Noise in Digital Microphones
Per Ove Almeflo & Magnus Johansson
Milab Microphones, Helsingborg, Sweden

A digital microphone has a high power consumption compared to an analog. This will result in a higher working temperature, especially if traditional linear regulators are used in the microphone power supply circuitry. For a better degree of power efficiency, a switch mode power supply can be used instead. A switch mode power supply will however add noise. If the pulse width modulator is synchronised to the analog-to-digital converter sample rate clock, the switch mode power supply noise decreases by elimination of the alias frequencies.
Paper 5341

17:30 hr H-9
Proximity Effect of Microphones
Emil Milanov & Elena Milanova
Consultants, Sofia, Bulgaria

In this article we discuss the proximity effect of electro-dynamic microphones with two acoustical entrances. The proximity effect is appearing when a directed microphone is getting closer to the sound source. It is described as an alteration of the frequency response and more specifically as an increase of the microphoneís sensitivity when the distance is decreasing. The reason for this change is the change of form of the sound wave from a plane to a sphere when the distance to the sound source is decreasing. The goal of this article is to determine the relationship of the proximity effect from the angle between the sound wave and the acoustical axis of the microphone.
Paper 5342


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