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WO1998002977A1 - Appareil et procede de mixage - Google Patents

Appareil et procede de mixage Download PDF

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Publication number
WO1998002977A1
WO1998002977A1 PCT/US1997/012393 US9712393W WO9802977A1 WO 1998002977 A1 WO1998002977 A1 WO 1998002977A1 US 9712393 W US9712393 W US 9712393W WO 9802977 A1 WO9802977 A1 WO 9802977A1
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WO
WIPO (PCT)
Prior art keywords
ultrasonic
frequency
ultrasonic wave
subsonic
sonic
Prior art date
Application number
PCT/US1997/012393
Other languages
English (en)
Inventor
Elwood G. Norris
Original Assignee
American Technology Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by American Technology Corporation filed Critical American Technology Corporation
Priority to AU36025/97A priority Critical patent/AU3602597A/en
Publication of WO1998002977A1 publication Critical patent/WO1998002977A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B11/00—Transmission systems employing sonic, ultrasonic or infrasonic waves
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K15/00—Acoustics not otherwise provided for
    • G10K15/02—Synthesis of acoustic waves
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R23/00—Transducers other than those covered by groups H04R9/00 - H04R21/00

Definitions

  • This invention pertains to compression wave generation. Specifically, the present invention relates to a device and method for indirectly generating a sonic or subsonic compression wave without the use of a direct radiating element at the source of the compression wave generation.
  • Sound waves in general are wave-like movements of air or water molecules. Because these media are elastic and generally homogeneous, naturally occurring sound travels in all directions radially from the source of generation.
  • a voice, instrument or impact for example, will radiate omni-directionally in a unitary, integrated form, carrying multiple frequencies, overtones, and a full range of dynamics that collectively contribute to an instantaneous sound perception at the ear.
  • This perception of naturally occurring sound at a healthy ear is deemed to be "pure” when it corresponds to the same acoustic content that existed at the point of origin. Because sound is a transient, temporary state of motion within a media, it is not self-sustaining.
  • thermodynamics require that the sound eventually dissipate its motion into heat or other forms of energy. Therefore, if storage or preservation of the sound is desired, it is necessary to transmute such motion into a fixed form of recording. This fixed form can then be recovered later by conversion of the fixed form back into sound waves.
  • a primary goal of modern acoustic science is to reproduce pure sound, based on conversion of the electronic, magnetic, mechanical or optical record into compression waves which can be detected an the ear.
  • the ideal system would play all original sound back through a resonating device comparable to that which produced the sound in the beginning.
  • the violin sounds would be played back through a violin, regenerating the overtones and a myriad of other dynamic influences that represent that instrument.
  • a piccolo would be played back through a device that generates the high frequencies, resonance aspects and overtones associated with this type of instrument.
  • a speaker is a transducer which receives energy in one form (electrical signals representative of sound) and translates the energy to another form (mechanical vibration) .
  • an electrical current that is proportional to the strength and frequency of the signal to be broadcast is sent through a coil attached to a rigid membrane or cone.
  • the coil moves inside a permanent magnet, and the magnetic field exerts a force on the coil that is proportional to the electrical current.
  • the oscillating movement of the coil and the attached membrane sets up sound waves in the surrounding air.
  • this same "pure" sound that arrives at the ear can be detected by a microphone and consequently recorded into a fixed media such as a cassette tape or compact disc.
  • the microphone diaphragm may not have the sensitivity of a human ear, modern technology has been quite successful in effectively capturing the full range of sound experience within the recorded signal. For example, it is unnecessary to provide separate microphones for recording both low and high range frequencies. Instead, like the ear drum, the microphone captures a unified sound waveform and registers this as a composite signal that can then be recorded onto an appropriate media.
  • the microphone is not the primary limitation to effective reproduction of "pure" sound. Rather, the challenge of accurate sound reproduction arises with the attempt to transform the microphone output to compression waveforms through a mechanical speaker. Accordingly, the focus of effort for achieving a unified sound system has been to develop a complex speaker array which is able to respond to high, medium and low range frequencies, combining appropriate resonance chambers and sound coupling devices, to result m a close simulation of the original sound experience.
  • the purpose of the speaker driver and diaphragm is to produce a series of compression waves by reciprocating back and forth to form a compression wave.
  • the initial design challenge is to compensate for resistance against movement m speaker response due to inertia within the speaker mass.
  • the mass will seek to stay in motion, causing the driver to overshoot, requiring further compensation for delayed response to reverse its direction of travel.
  • This conflict of mass and inertia recurs thousands of times each second as the speaker endeavors to generate the complex waveform of the original sound embodied in the electrical signal received.
  • Electrostatic loudspeakers represent a different methodology. Unlike the electrodynamic loudspeaker with its cone shaped diaphragm, the electrostatic loudspeaker uses a thin electrically conducting membrane Surrounding the plate are one or more fixed grids. When a signal voltage is applied to the elements, the electrostatic force produced causes the diaphragm to vibrate. This low-mass diaphragm is particularly useful as a high-frequency radiating element, and its operation can be extended to relatively low frequencies by the use of a sufficiently large radiating area.
  • electrostatic speakers offer some advantages, they are huge, inefficient and suffer from the lack of point source radiated sound. For example, sound detection is accomplished by a microphone at a localized or point source. To convert the detected sound to a non-point source such as a large electrostatic diaphragm may create an unnatural sound reproduction. Specifically, a radiating element 5 feet in height is limited in its ability to simulate the delicate character of a piccolo or violin.
  • phase shift introduced because of the differences in time delay for high frequency signals traveling the shorter distance of the cone of a tweeter to a listener, versus ( i) the substantially longer path for low frequency signals from the horn or woofer speaker to a listener's ear can be in the range of thousands of percent m phase differential.
  • Yet another object of the invention is to generate a sonic or subsonic compression wave without having to overcome the mass and associated mertial limitations of a conventional direct radiating element.
  • Yet another object is to omni-directionally generate a high frequency compression wave, thereby avoiding the highly focused and directional nature of high frequency signal emissions typical of a conventional loudspeaker.
  • Still yet another object is to generate a sonic or subsonic compression wave in a localized area without coupling to an associated environment or enclosure which would otherwise cause undesirable broadcasting of the sonic or subsonic compression wave.
  • Yet another object is to generate a sonic or subsonic compression wave wherein characteristics of the sonic or subsonic compression wave are not limited by the characteristics of a direct radiating element.
  • Another object of the invention is to emulate a sound wave detection process typical of a poin -source detection device such as a microphone, but without providing a physical detection device at a detection location.
  • Another object is to control the volume of a sonic or subsonic compression wave by manipulating the degree of interaction of the at least two ultrasonic compression waves.
  • Still another object is to emit a sonic or subsonic compression wave from a region of air as a by-product of an ultrasonic compression wave being emitted from a single ultrasonic transducer into the region.
  • the present invention is embodied in at least two different systems, each using a different method for indirectly generating sonic or subsonic sound waves.
  • a sonic or subsonic compression wave is emitted from a region of interference of at least two ultrasonic compression waves.
  • the principle of operation is based on generating a by-product of interference of the at least two ultrasonic compression waves.
  • the interference generates a by-product which is the difference in frequency between the compression waves .
  • a system which demonstrates this by-product concept is comprised of two ultrasonic emitters which are oriented so as to cause interference between emitted ultrasonic compression waves.
  • a sonic or subsonic compression wave equal to this difference is generated from within a region of interference.
  • the different embodiment of the system provides the advantage of only being comprised of a single ultrasonic direct radiating element.
  • the advantage is not only the decreased amount of hardware, but the perfect alignment of the two interfering ultrasonic compression waves because they are emitted from the same radiating element.
  • the sonic or subsonic wave train appears to be generated directly from the ultrasonic emitter. If it were not for the inescapable conclusion that the ultrasonic emitter cannot generate sonic or subsonic frequencies, plus the audible evidence that the sound is not emanating directly from the emitter, one might be deceived.
  • the importance of the first embodiment is that it teaches the concept of generating a sonic or subsonic wave train as a result of the interference between two ultrasonic wave trains. In essence, it is easier to see that two ultrasonic wave trains are coming from two ultrasonic emitters. But the principle of generating a new compression wave from two ultrasonic compression waves prepares the way for understanding how the second embodiment functions.
  • a key aspect of the invention is the discovery that by superimposing sonic or subsonic intelligence onto an ultrasonic carrier wave, this intelligence can be retrieved as a new sonic or subsonic wave train. Whether the ultrasonic wave trains are generated from two emitters or from a single emitter, the effect is the same .
  • the present invention eliminates a direct radiating element as the source of a compression wave so that the desired sound is generated directly and distortion free from a region of air.
  • the present invention has proven to affect a large number what are sometimes perceived as unrelated topics.
  • a list is provided which highlights the aspects which have already been introduced as well as the aspects yet to be revealed hereafter.
  • These aspects of the invention include 1) indirectly generating a sonic, subsonic or ultrasonic compression wave, 2) superimposing intelligence on an ultrasonic carrier wave and retrieving the intelligence as the indirectly generated compression wave, 3) causing at least two ultrasonic compression waves to interact in air and using the by-product of the interference, 4) generating the compression wave from a relatively massless radiating element (air) to avoid the distortion and undesirable harmonics of conventional direct radiating elements, 5) affecting a physical state of a living being by generating subsonic frequencies in close proximity thereto, 6) generating approximately a near point-source of sound, 7) eliminating distortion in playback or broadcasting of sound, 8) eliminating the "beaming" phenomenon inherent in emission of high frequency compression waves from a direct radiating element, 9) generating a sonic or subsonic compression wave which is
  • Figure 1 is a block diagram of the components of a loudspeaker assembly of the state of the art .
  • FIG. 2 is a block diagram of the components of an indirect compression wave generation system which is built in accordance with the principles of one embodiment of the present invention.
  • Figure 3 is an illustration of the indirect compression wave generation using the apparatus of FIG. 2, including the interference effect which generates the desired sonic or subsonic compression wave.
  • Figure 4A is a graph showing frequency drift which alters the desired compression wave when two separate frequency generators are used.
  • Figure 4B is a graph showing how frequency drift becomes irrelevant f both compression waves drift together .
  • Figure 5 is an alternative embodiment of the present invention using two separate frequency generators .
  • Figure 6 is an alternative configuration of ultrasonic transducers to indirectly generate compression waves.
  • Figure 7 is another alternative configuration of ultrasonic transducers to indirectly generate compression waves.
  • Figure 8 is an illustration of the preferred embodiment of the present invention which only requires a single ultrasonic emitter to indirectly generate compression waves .
  • Figure 9 is an alternative emboidment of FIG. 8.
  • Figure 10 is an illustration of a resonant cavity with two ultrasonic signals being emitted inside to interact .
  • Figure 11 is a diagram of new headphones and the human ear as the resonant cavity.
  • Figure 12 illustrates a system for recording sound without having to provide a physical microphone element at a compression wave sensing location.
  • Figure 13 is a graph showing how air responds increasingly non-lmearly as the amplitude or intensity of sound increases.
  • Figure 14 is a graph showing when air responds non- lmearly to a specific signal of a defined frequency and amplitude .
  • Figure 15 is an embodiment which teaches reflection of the ultrasonic frequency signals to develop acoustical effects.
  • a direct process is defined as causing a radiating element 10 to vibrate at a desired frequency as shown in FIG. 1.
  • the system of FIG. 1 is typically used to directly generate audible and inaudible compression waves, both above and below the range of human hearing.
  • a conventional compression wave generating system is thus comprised of a speaker element 10 which can be any dynamic, electrostatic or other direct radiating element, and a signal source such as a signal generator or amplifier 12.
  • the signal source 12 supplies an electrical signal representative of a compression wave having a specific frequency or frequencies at which the speaker element 10 will vibrate to produce compression waves 14.
  • the loudspeaker 10 functions as a transducer trying to accurately reproduce sound recorded in an analog or preferably a digital format by converting an electrical signal into compression waves 14. Therefore, until now, generating compression waves has been a direct process as previously defined.
  • the reproduced sound is generated directly by a physical radiating element which vibrates at the frequency or frequencies of the electrical signal which drive i .
  • This vibration typically drives a loudspeaker cone or diaphragm which creates the compression waves 14 which the human ear can hear when within the range of 20 to 20,000 cycles per second. For example, the diaphragm vibrates at 1500 cycles per second to generate an audible tone of 1500 Hz.
  • a “signal source” will interchangeably refer to a “signal generator” or “amplifier” which provide electrical signals representative of compression waves to be emitted from a speaker.
  • the term “speaker” will interchangeably refer to the terms “transducer”, “emitter”, “loudspeaker”, “diaphragm”, “physical radiating element” or “direct radiating element” which convert the electrical signals to a mechanical vibration causing compression waves.
  • compression wave will interchangeably refer to the terms “sound wave”, “longitudinal wave” and “wave train” which are sonic, subsonic and ultrasonic waves propagating through a transmission medium such as air.
  • the present invention in a preferred embodiment teaches a method and apparatus for indirectly generating a compression wave.
  • Indirect generation refers to the absence of a direct radiating element at the source of the compression wave generation.
  • air molecules are caused to vibrate at the desired sonic, subsonic or ultrasonic frequency to thereby function as the radiating element and generate the compression wave.
  • the air itself becomes the direct radiating element, and the air is caused to vibrate indirectly.
  • the present invention 1) makes use of at least two ultrasonic signals, 2) superimposes a desired sonic or subsonic signal onto one or both of the ultrasonic signals, 3) emits the ultrasonic signals from at least one ultrasonic emitter 4) causes the ultrasonic signals to interfere, and 5) generates a new compression wave from a region of interference of the ultrasonic compression waves.
  • Indirect compression wave generation is accomplished in a first embodiment as illustrated in FIG. 2.
  • the fundamental elements of the system include at least two ultrasonic acoustical transducers 20, an ultrasonic signal source 22, a means for combining signals 24, and an input 26 to the means for combining signals which provides a signal to be superimposed upon a carrier signal.
  • the ultrasonic signal source 22 also functions as a means for controlling the frequency of signals being emitted from the at least two ultrasonic acoustical transducers 20.
  • the dotted line 28 indicates that in this first embodiment, the orientation of the transducers 20 are coaxial for purposes to be explained.
  • the apparatus above is able to function as described because of an unexpected result of applying the beat principle. It is well known that two audible sounds having different frequencies can interfere to generate a beat frequency. The number of beats per second equals the difference of the frequencies of the component (fundamental) waves. The present invention uses this principle to obtain the unexpected result that this beat or by-product can carry extractable intelligence if the fundamental waves are ultrasonic.
  • the method of superimposing the sonic or subsonic compression wave onto the at least two radiating element system of FIG. 2 specifically involves a frequency difference or sweeping technique. In other words, a first ultrasonic carrier wave 30 might be kept steady at 40 KHz.
  • the second ultrasonic carrier wave 32 can, for example, be swept from 40 KHz up to 41 KHz, and then back down again.
  • the listener hears a wavering tone, where the compression wave correspondingly varies in its range of frequency from 0 Hz up to 1 KHz and then back down to 0 Hz.
  • the formula which expresses the formation of the compression wave s / ne réelle /, - f ⁇ .
  • the ultrasonic wave f 2 is the ultrasonic wave which is carrying the intelligence m the form of the superimposed compression wave.
  • the ultrasonic wave f- is the base carrier wave which typically will not vary, but can also be varied if desired.
  • the preferred transmission medium of the present invention is air because it is a highly compressible medium that easily responds with a beat frequency. However, any fluid can function as the transmission medium if desired.
  • FIG. 3 shows the generally coaxial and interfering ultrasonic compression waves 30, 32. It may be assumed that the transmission medium is air A region of interference 34 is shown where the two ultrasonic waves 30, 32 interact. The interference in this region results in a compression wave 36 which is not a new wave, but rather exists only under the beat frequency principle. This compression wave 36 radiates generally outward in all directions (omni- directionally) from this region of interference 34.
  • the audible compression wave 36 (if the difference in frequency is sonic) radiating omni -directionally outward from the region 36 of air where interference occurs. It is further noted that the compression wave appears to be enhanced where the superposition is reflected from a surface such as a table, ceiling or wall. This phenomenon may be utilized to bring a perception of multi-dimensionality to sound reproduction.
  • One of the unexpected aspects of the present invention is that it is using the by-product of interference and manipulating the ultrasonic carrier waves so that the by-product carries intelligence.
  • compression wave applications try to minimize or eliminate any by-product which might be formed as a consequence of their use .
  • the present invention distinguishes itself from the prior art by doing just the opposite- -it maximizes the by-product to produce a wave component.
  • the intelligence being referred to above is any compression wave which carries information which may be extracted therefrom.
  • the compression wave might be in the audible range of human hearing, and could be a radio transmission such as might be received by a receiver in a stereo sound system or in a car.
  • the compression wave could be subsonic .
  • the invention performs more efficiently when the ultrasonic carrier waves are higher in frequency. This is understandable when realizing the mechanism by which the compression wave is being generated. Molecules of air are being caused to vibrate at the frequency of the compression wave, which is a direct result of movement of the air by the carrier waves.
  • the ultrasonic carrier waves more efficiently couple to the air molecules at higher ultrasonic frequencies than at lower ultrasonic frequencies, thereby obtaining the advantage of enhanced efficiency with higher frequency.
  • volume or amplitude of the compression wave is controlled by several factors.
  • One factor is the energy contained within the ultrasonic carrier waves. Obviously, the energy for the compression waves must necessarily come from the ultrasonic carrier waves. An ultrasonic carrier wave with a higher velocity contains more energy than an ultrasonic carrier wave with a lower velocity.
  • Amplitude is another factor which affects the volume of the compression wave. Greater amplitude of the ultrasonic compression waves results in greater amplitude of the compression wave.
  • Transducer orientation also greatly affects the compression wave. It has been stated that the ultrasonic carrier waves must interact to generate the compression wave. However, there are many degrees of interaction.
  • the orientation shown in FIG. 2 is of two transducers 20 which are generally maximizing interference by turning emitting surfaces directly towards each other and then orienting the transducers so as to be coaxial with respect to the emitted ultrasonic carrier waves.
  • the orientation of ultrasonic transducers 20 in FIGs . 6 and 7 show that orientation might vary greatly.
  • FIG. 6 shows two ultrasonic acoustical transducers 20 oriented substantially parallel to each other, but creating ultrasonic signals (and emphasized by paths 70) which eventually cross at some distance from the transducers 20.
  • FIG. 7 Another orientation of the transducers 20 is shown in FIG. 7 which varies from the orientation shown in FIG. 6 in that axes of the ultrasonic compression waves 30, 32 following paths 70 do not actually cross, but are sufficiently close such that the fringe of the waves 30, 32 sufficiently interfere to enable generation of the compression wave.
  • FIG. 2 it should also be observed that there is an advantage to using one signal source 22 to generate the ultrasonic compression waves 30, 32 to be emitted by the ultrasonic transducers 20.
  • the advantage of this arrangement is that signal differences that might otherwise occur due to variations in temperature or performance of two separate signal sources would likely lead to drift between the frequency values of the waves 30, 32.
  • a single ultrasonic signal source 22 is generating both output signals 30, 32 so that they will drift together if at all, and thus make it easier to control the compression wave.
  • FIG. 4A is a graph showing ultrasonic carrier waves 30 and 32.
  • the desired compression wave is a tone of 1 KHz, represented by the designation 50.
  • the difference in frequency between ultrasonic compression waves 30 and 32 will generate this tone.
  • wave 32 is shown to be drifting upward in frequency by an amount designated as 51. Consequently, the compression wave will have a tone designated by the difference in frequency designated as 52 instead of 51.
  • FIG. 4B illustrates the effect of using a single ultrasonic signal source 22 (FIG. 1) .
  • the ultrasonic carrier waves 30, 32 are shown to drift together, resulting in an overall net change in frequency of zero because they are separated by a distance 50 of 1 KHz before, during and after drifting.
  • a frequency control device 24 was also previously mentioned as being necessary for concurrently operating the ultrasonic acoustical transducers 20 The frequency control device 24 can perform the function of altering one or both of the ultrasonic signals 30, 32 being generated by the ultrasonic signal source 22.
  • the frequency control device 24 superimposes the first ultrasonic compression wave 30 with a desired electrical signal representing the desired compression wave frequency or frequencies 36
  • the combination is defined as the sum of the frequencies of the first ultrasonic compression wave 30 and the desired compression wave frequency or frequencies and is emitted as the second ultrasonic signal 32.
  • the final elements of the system shown in FIG. 2 are the two ultrasonic transducers 20. These ultrasonic transducers 20 emit compression waves at ultrasonic frequencies using devices such as piezoelectric transducers. There is one basic observation which makes the advantage of using ultrasonic acoustical transducers 20 more significant.
  • the present invention advantageously emits ultrasonic signals which result m only one audible compression wave being generated as a by-product of the interference between the ultrasonic compression waves .
  • FIG. 5 illustrates the observation that there are other ways to deliver electrical signals representing the ultrasonic compression waves 30, 32 to the ultrasonic transducers 20 instead of using a single ultrasonic signal source 22.
  • two separate ultrasonic sources 40, 42 might be provided as shown in FIG. 5, although the risk of frequency drift becomes more relevant.
  • This embodiment might also require some type of synchronization between the two ultrasonic signal sources 40, 42.
  • a synchronizing controller 44 might coordinate transmission of the two ultrasonic signals 30, 32.
  • the embodiment of FIG. 2 teaches the principle that interfering waves 30, 32 generate a compression wave which is carrying intelligence as the difference in frequency between them.
  • a compression wave is generated which has a frequency equal to the difference m frequency of the interfering waves.
  • This embodiment is shown as FIG. 8, and is structurally different from the preferred embodiment because it is possible to generate the compression wave as a result of interfering ultrasonic carrier waves, but only using one radiating element.
  • the first ultrasonic carrier wave f x may be assumed to be the ultrasonic compression wave being generated by the signal source 22.
  • the second ultrasonic compression wave is the combination of the first ultrasonic compression wave and a sonic or subsonic which is wave superimposed upon it by amplitude modulation. Subtracting the first ultrasonic wave from the second amplitude modulated ultrasonic wave results in the indirect generation of the compression wave. Although seemingly being emitted from the single ultrasonic emitter 20, the sonic or subsonic compression wave is still the by-product of the interference of ultrasonic compression waves.
  • the elements of the system shown in FIG. 8 include the ultrasonic transducer 20 generating the ultrasonic carrier wave 60 with the desired intelligence amplitude modulated thereon.
  • the resulting compression wave 36 is shown being generated from the carrier wave 60.
  • Supplying an ultrasonic signal to the apparatus is an ultrasonic signal source 22.
  • the ultrasonic carrier wave generated therefrom is sent to an amplitude modulator 62 which amplitude modulates a sonic or subsonic signal 64 onto the ultrasonic compression wave 60.
  • the first embodiment superimposes a desired sonic or subsonic signal onto a carrier wave which is expressed as a sweeping of frequencies.
  • a single emitter of the preferred embodiment functions to generate the compression wave when the desired sonic or subsonic signal (compression wave) is amplitude modulated onto the ultrasonic carrier wave.
  • compression wave compression wave
  • the later, preferred embodiment may give the mistaken impression that an ultrasonic transducer is somehow spontaneously generating bass frequencies. This misconception arises, however, because the interference of the two ultrasonic compression waves is occurring generally directly m front of the ultrasonic transducer 20.
  • FIG. 9 is provided to show more intuitively that two separate and distinct ultrasonic compression waves (carrier waves) are being generated from separate signal sources 22, and then remitted from the transducer 20 to generate the desired compression wave .
  • the present invention teaches a method for indirectly generating at least one sonic or subsonic frequency from the transmission of at least two ultrasonic frequencies of different value which interact.
  • the ultrasonic frequencies can be generated from a single emitter or from at least two emitters, but the method of superimposing intelligence on the carrier waves varies depending upon the number of emitters being used. If two emitter are being used, then the desired frequency is varied by sweeping through a desired frequency range. However, if one emitter is used, the method comprises amplitude modulating a desired sonic or subsonic signal onto the ultrasonic compression waves.
  • the present invention also generates sound from a nearly massless radiating element which is at all times in motion and which only shifts a small percentage of its fundamental frequency in order to co-generate frequencies which span the entire audio spectrum.
  • a nearly massless radiating element which is at all times in motion and which only shifts a small percentage of its fundamental frequency in order to co-generate frequencies which span the entire audio spectrum.
  • the great significance of this aspect is readily grasped by those who have endeavored unsuccessfully to create a radiating element free of distortion effects caused by the radiating element itself. For example, harmonics on a loudspeaker cone, cone overshoot and cone undershoot caused by inertia, and the imperfect surface of the cone are all factors which contribute to signal distortion attributable to a direct radiating element.
  • a direct physical radiating element has other undesirable qualities as well.
  • the frequency response of a direct radiating element is not truly flat, but instead is a function of the specific band of frequencies which it is inherently best suited for To achieve a flat response, manufacturers have gone so far as to construct loudspeaker cone material from Kevlar in an attempt to try and dampen undesirable harmonics and improve fidelity.
  • the present invention does not require such extreme measures because there is no physical direct radiating element.
  • the radiating elements which are essential to the system are ultrasonic transducers which are inherently less susceptible to the distortion effects found in lower frequency radiating elements .
  • This aspect of indirect sonic or subsonic compression wave generation of the present invention provides a giant step toward achieving truly indirect sound reproduction with original sound quality. While the state of the art has advanced the ability to convert an analog signal to a digital recording, and to even process the signal digitally, the quality of sound reproduction has always been limited by the mechanical speaker element. This is no longer the case because the present invention achieves truly distortion free sound which is not hindered by the mass and associated mertial limitations of a radiating element.
  • Another aspect is that affecting living beings gives rise to the possibility of unobtrusively generating crowd- controlling subsonic sound waves.
  • Very low frequencies such as those around 12 Hz, have been shown to nauseate or disorient human beings and other animals. This principle may have applications in crowd control .
  • Other aspects of the invention include the advantages of providing approximately a near point - source of sound.
  • the present invention substantially eliminates phase distortion created by multi-speaker systems designed to more efficiently reproduce the various frequencies of sound.
  • the advantage of this aspect is the ability to accurately reproduce the effect of point-source sound with a highly directional sense of orientation for the listener. This is the ultimate goal of sound reproduction which until now has never been fully realized.
  • Another aspect of the present invention is the orientation of the ultrasonic transducers 20.
  • the present invention functions best when there is maximum interference of the ultrasonic carrier waves by emitting the carrier waves coaxially
  • This orientation is inherent m a single emitter system.
  • this orientation is best achieved in a two emitter system by orienting them to be diametrically opposite so as to present two emitting faces which are generally coaxial.
  • This is essentially the orientation of the ultrasonic acoustical transducers 20 as shown in FIGs . 2 and 5, and indicated by dotted line 28. This orientation guarantees the greatest amount of interaction because there is interaction along the entire path of the ultrasonic compression waves.
  • the ultrasonic transducers 20 are generally not subject to many of the limitations and drawbacks of all physical radiating elements described in this specification. Because the ultrasonic acoustical transducers 20 are only required to operate at extremely high frequencies, the distortion, harmonics and other undesirable features of a direct radiating element are inherently not as prevalent .
  • the present invention can generate the entire range of audible sounds, yet the ultrasonic transducer need only shift in frequency a small percentage (i.e. a 180 to 20,000 cycle shift produces the entire audio spectrum) .
  • a small percentage i.e. a 180 to 20,000 cycle shift produces the entire audio spectrum.
  • This favorable character has been known, however, it has not been possible to take advantage of the improved characteristics of an ultrasonic radiating element simply because these frequencies have generally had no impact on audible sound reproduction.
  • This invention thus makes it possible for sound reproduction to benefit from these relatively distortion free ultrasonic transducers in the sonic and subsonic spectrum.
  • Another aspect of the invention is the generation of unified audio frequency range signals. This is a signal which contains frequencies over the low, intermediate and high audio frequencies.
  • this type of signal represents frequencies which are those common for voice communication and musical tone reproduction which are typically broadcast by loudspeaker systems. This is accomplished by superimposing or mixing the audio frequency range signals with one of the ultrasonic compression waves. If the respective ultrasonic compression waves have the same frequency, and one compression wave also has the audio signal mixed with it, the audible compression wave generated after interaction of the carrier waves is just the unified audio range frequency signal.
  • the present invention eliminates the need for a phase-distorting cross -over network.
  • the present invention will generate all of the audible frequencies from approximately a near point -source at the intersection of the two ultrasonic compression waves. Consequently, the distortion caused by cross-over networks is also eliminated, along with the associated circuitry, thus saving space, cost and materials.
  • An additional aspect of the invention is the ability to generate sound within a broadly resonant cavity 80 as shown in FIG. 10.
  • a resonant cavity 80 is any cavity 80 which enables compression waves to interact within a chamber which amplifies and resonates. This means that at least two ultrasonic compression waves 82 can be emitted into the cavity 80 from any perspective.
  • two ultrasonic transducers 20 are emitting signals 82 into the cavity 80.
  • the compression waves 82 will be reflected off the walls and interact because of the dimensions of the cavity 80.
  • a single ultrasonic emitter can be used to generate the desired compression wave, where the broadly resonant cavity 80 acts to enhance or amplify the effect.
  • this aspect of reflection tends to emphasize or amplify the audio signal, giving a sense of source location to the sound.
  • This feature may be applied to develop a moving point sound source which can be controlled for audio effect. For example, a train sound can literally be caused to move through a theater by projecting or reflecting the ultrasonic beam from a wall or moving object. Other techniques of controlling location of the point source of sound are envisioned, such as controlled intersection of beams.
  • a resonant cavity being described is the human ear canal. Not only is the human ear extremely sensitive, but the ear canal itself can function as an environment forcing interaction of the compression waves as required by the present invention.
  • These observations provide an ideal application of the present invention and are shown generally in FIG. 11 as an ear piece 84 for hearing aids or headphones 86 for speech or music listening.
  • the small size of the ultrasonic transducer enables the direct insertion at the ear canal, and the resonant cavity 80 provides an ideal environment for reproduction of the original sound without a physical direct radiating element.
  • one or two ultrasonic transducers 20 can be disposed near each ear and oriented to emit compression waves into the ear canal.
  • a related application of the invention involves the emission of a signal which is audible only in the intended listener's ear from a distance. By targeting the desired listener's ear a selective audience can be designated without others being able to hear the transmission. Under prior art techniques, this discreet type of audible transmission required a receiver and speaker assembly to be disposed on the person receiving the signal. Such a system was difficult to conceal. However, precise reception of two ultrasonic carrier waves at the ear of an intended recipient eliminates the need to carry a receiver and speaker assembly. Another aspect of the invention relates to noise pollution.
  • boombox to refer to portable stereo systems which have relatively large bass speakers.
  • the boombox derives its name from the annoying side affect of a booming and repeated "thump" of the bass speakers driving large volumes of air.
  • the term is also sometimes used to refer to a car or other vehicle with even larger bass speakers. Because the speakers are integrally attached to an enclosure, the vehicle or its frame, the car itself becomes a radiating element.
  • the nature of the low frequency range also means that the it is the most amplified of all the frequency ranges by the vehicle. Consequently, persons outside the vehicle will be hit with wave upon wave of dull thumping sounds, a nuisance at best.
  • the present invention can thus advantageously eliminate the coupling of the vehicle to the radiating element by generating sound in midair within the vehicle.
  • the listener inside a vehicle can still enjoy the experience of loud bass frequencies; however, the frequencies will not be directly coupled to the enclosure because the radiating element is now a point in air. This means that the undesirable broadcasting effect into the environment beyond the immediate vicinity of the listener is significantly reduced.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • Audiology, Speech & Language Pathology (AREA)
  • General Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Circuit For Audible Band Transducer (AREA)

Abstract

La présente invention porte sur l'émission de nouvelles ondes de compression sonores ou infrasonores à partir de la zone d'interférence d'au moins deux trains d'ondes ultrasonores (30, 32). Dans un mode de réalisation, deux émetteurs ultrasonores (20) sont orientés de manière à provoquer une interférence entre les trains d'ondes ultrasonores émis (30, 32). Lorsque la différence de fréquence entre les deux trains d'ondes ultrasonores (30, 32) se trouve dans la gamme des fréquences sonores ou infrasonores, un nouveau train d'ondes sonores ou infrasonores de cette fréquence est émis depuis la zone d'interférence. Selon le mode de réalisation préféré, le système comprend une seule source ultrasonore (20) qui émet plusieurs ondes. Un aspect essentiel de la présente invention consiste à superposer des signaux sur au moins l'une des ondes porteuses ultrasonores. Ces signaux peuvent ensuite être extraits sous la forme d'un nouveau train d'ondes de fréquence sonore ou infrasonore, lequel est produit par l'interférence d'au moins deux ondes porteuses de fréquence ultrasonore.
PCT/US1997/012393 1996-07-17 1997-07-16 Appareil et procede de mixage WO1998002977A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU36025/97A AU3602597A (en) 1996-07-17 1997-07-16 Acoustic mixing device and method

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US68350496A 1996-07-17 1996-07-17
US08/683,504 1996-07-17

Publications (1)

Publication Number Publication Date
WO1998002977A1 true WO1998002977A1 (fr) 1998-01-22

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PCT/US1997/012393 WO1998002977A1 (fr) 1996-07-17 1997-07-16 Appareil et procede de mixage

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Country Link
AU (1) AU3602597A (fr)
WO (1) WO1998002977A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7369100B2 (en) 2004-03-04 2008-05-06 Eastman Kodak Company Display system and method with multi-person presentation function

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1616639A (en) * 1921-06-03 1927-02-08 Western Electric Co High-frequency sound-transmission system

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1616639A (en) * 1921-06-03 1927-02-08 Western Electric Co High-frequency sound-transmission system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7369100B2 (en) 2004-03-04 2008-05-06 Eastman Kodak Company Display system and method with multi-person presentation function

Also Published As

Publication number Publication date
AU3602597A (en) 1998-02-09

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