Session H Sunday, May 13 13:30 - 18:00 hr Room C/D
Microphones
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 (�auralize�) 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 microphone�s 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
