Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Plural or compound reproducers
Reexamination Certificate
1998-02-12
2001-04-10
Le, Huyen (Department: 2743)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Plural or compound reproducers
C381S300000, C381S386000
Reexamination Certificate
active
06215883
ABSTRACT:
BACKGROUND OF THE INVENTION
My invention concerns interaural time delay of a direct sound superimposed wavefront as it is generated by a loudspeaker array and is perceived by the ears and brain to have a distinct spheroidal propagation and thus, a corresponding radius vector and thus, a psychoaccoustic virtual point-source, hereafter referred to as an image, in three dimensional space.
Space and source perception of human hearing in nature, as well as with reproduced sound, depend concurrently on at least four different parameters of acoustics which are received by the left and right ears and processed in the hearing center in the brain to identify a sound's point-source, not only as to direction, but also in rather exacting distance estimation, i.e. to find the radius vector of a given wavefront.
These four parameters, as long understood, may be listed as loudness (amplitude of a given soundwave); the acoustic ratio (ratio in amplitude of direct to reflected soundwaves); high frequency roll-off (absorption by the atmosphere of energy of shorter wavelengths); and finally, and most significant for image perception, time delay, or the relative difference in times of arrival of a given wavefront (at the same period of phase) at the two respective ears.
In order to explain the physics of creating an image one must note that time delay may be understood to exist in two regions of effect on human hearing. The proportion of the human interaural separation (approximately 15 to 21 cm.), to the audible wavelengths (which vary from approximately 1,720 cm. to 1.72 cm.) may fall into the region referred to as near-field, meaning an interaural phase-shift of time delay which is well within one full cycle of a given wavelength, and which is intelligible by the brain as to degree. On the other hand, this proportion may fall into the region referred to as far field, meaning a phase-shift of time delay which is greater than 360° (one full cycle of a given wavelength), or else very near 0° in the near field which is beyond comprehension to the brain with respect to the oncoming radius vector of a direct wavefront. This far-field proportion is, however, very useful for the spatial reconstruction of reflective walls and other surrounding surfaces in a recorded non-anechoic environment. This use of echo, which may be effective from 10 to 30 ms., is known as the Haas effect and is employed by the recording industry as the primary tool for building a “stereo” as well as “surround” soundstage.
On the other hand a direct oncoming wavefront received by the ears in an anechoic condition, i.e., with no reflective surround echo clues, may be subconsciously measured by the brain as to the phase-shift of the arrival times with respect to the tangent of the wavefront at the two ears. Although the difference may be as little as one tenth of a millisecond, in the near field region (which, with an interaural separation of 15-21 cm., lies between approximately 125 HZ (wavelength=275 cm.) and 1500 HZ (wavelength=23 cm.)), this delay may correspond to a comprehensible amount of phase shift (that is greater than 0° and less than 360°), which may be used to triangulate the angle of the oncoming wavefront to the head, using the following relationship:
Sin
Θ
=
ct
x
where
&thgr; is the arriving angle of the radius vector of the oncoming wavefront;
c is the speed of sound;
t is the time delay; and
x is the distance between the ears.
Furthermore, by slightly “cocking” the head to the first found angle, the brain may refine this estimation in three-dimensional space, subconsciously and nearly simultaneously, triangulating several aspects of the wavefront, and thus, the curvature or radius, ie., with a flatter wavefront signalling a more distant point-source and more rounded wavefront signalling a nearer point-source.
DESCRIPTION OF THE PRIOR ART
Prior art (See particularly, U.S. Pat. No. 3,773,984) from Peter Walker of Quad Electroaccoustics Ltd, Huntingdon, England, provides for an arrayed loudspeaker, marketed as the Quad ESL-63 Electrostatic Loudspeaker, which involves a vibrating electrostatically charged thin membrane which is suspended in a plane between two like-dimensioned planar electrode grids which, in turn, are electrically segregated into an array of concentric annular segments surrounding a central circular section.
A mono signal drives the central section with no delay and then, in the fashion of a transmission-line loudspeaker (a parallel line of capacitors linked with inductance, which introduces a progressive amount of delay), drives the inner most ring-segment with a given amount of delay and then, each with an additional given amount of delay, drives each additional ring-segment outward from the center until the outer most ring-segment has been activated.
Thus, the superimposed wavefront generated by the Walker device propagates in a substantially spherical pattern which has a fixed radius and therefore may be perceived to describe an image which occupies a fixed and stable point in three-dimensional space, approximately two meters behind the loudspeaker device.
My invention, with the guidance of data on a positioning track and a computer processor achieves the creation of a stable image at a point in three-dimensional space at an arbitrarily chosen location behind (and including the plane of) the device and then provides means for shifting the location to any other arbitrary location behind the device.
SUMMARY OF THE INVENTION
A cinema sound reproduction device is described which when fed by an ordinary monaural input will produce a phase coherent spheroidally shaped wavefront which may be perceived by the listener as having a distinct image at an apparent point in three dimensional space, which is positioned some variable distance and direction behind the actual position of said device.
The architectural sub-structure of this invention may be implemented in different ways. One such implementation may be an articulated compound spheroidal hinge construction of multiple sixteen-sided polyhedra composed of only equilateral triangles of identical size. Each hinged polyhedron, in turn, may serve as a platform for the mounting of one or more identical lower-midrange conventional loudspeakers. All of the loudspeakers in the array are simultaneously driven in phase, producing wavefront elements which superimpose upon one another to form a combined, or superimposed, wavefront which is heard by an observer to emanate from a source point on the central axis of the array of loudspeakers, such that the distance of the source point is dependent upon the configuration of the articulated spheroidal hinge. The loudspeakers are arrayed in a spheroidal section which has one and only one focal point, and the sound from the loudspeakers in that spheroidal configuration appears to emanate from that focal point.
Alternatively the architectural sub-structure of this invention may be a fixed array of identical lower-midrange loudspeakers, sufficient in number to form a single center loudspeaker, plus other surrounding groups of loudspeakers, more or less concentric to the center loudspeaker, utilizing a calculated delay for each individual loudspeaker.
In this case, a processor executes mono signals which are fed to the center loudspeaker at minimum delay and then with progressive, calculated delays, successively to each loudspeaker toward and including the outermost ones.
In either form of architectural sub-structure, a phase-coherent superimposed spheroidal wavefront produced by said individual loudspeakers may be varied with respect to radius in a continuous way to define a predetermined apparent point in space as the virtual point source, or image, of the wavefront, and then, when the radius is varied, a different apparent point in space becomes the new virtual point source.
This is a psychoacoustic image. It may be seen (or heard) to be the radius of the spheroidal wavefront. It may be located anywhere behind said device from infinity to within the plane of the device.
The perc
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