Every aspect of electronic reproduction of sound has enjoyed significant technological advances during the past 50 years with one exception -- the loudspeaker. Consumer playback equipment has evolved from the mechanical phonograph record to the cassette tape to CD and now DVD. Recording devices first used wire, then magnetic tape, and now use digital audio tape, computer hard disks, and memory chips. Electronics migrated from tubes to transistors to the digital technology of today. Improvements have eliminated wow & flutter, turntable rumble, L/R crosstalk, and a host of other undesirable artifacts. Noise and distortion have been reduced to imperceptible levels.
Basic loudspeaker operating principles, however, have remained unchanged for more than 70 years. Since 1925, when C.W. Rice and E.W. Kellogg described basic, direct-radiating speaker parameters, there have been few, if any, fundamental changes in speaker design or in the way in which electrical impulses are converted into sound. Despite its long life and the efforts made to improve it, the familiar, wide-range high-fidelity loudspeaker typically is less than one percent efficient, and its reproduction quality is largely dependent upon the size and kind of enclosure, with smaller versions generally producing inferior sound.
What if a technology could be developed that would eliminate the undesirable artifacts of loudspeaker systems. Think about an audio reproduction system that could produce the broad range of frequencies required for human hearing with no direct radiating transducer devices, no crossovers, a single point source for the entire frequency spectrum, no cone or cabinet resonances, no measurable distortion, 10% electrical to acoustical efficiency, and reduced weight, size, and cost.
HyperSonic Sound IS:
HyperSonic Sound is NOT:
These days it is highly unusual to find something that is truly original. The terms ìquantum leap and paradigm shiftî are so overused that, when one runs across a technology that is truly worthy of such a description, few believe it.
Fortunately, like all extraordinary developments, this elegant technology can be described with an economy of words.
The Norris Acoustical Heterodyne technology projects silent ultrasound energy which the inventor, Elwood Woodyî Norris, refers to as HyperSonic Soundî (HSS ™) that emerges as audio from whatever reflective surface it strikes. The sound is actually created in mid-air. This is not an illusion. The acoustical sound wave is created directly in the air molecules by down-converting ultrasonic energy to the frequency spectrum we can hear.
The effect is produced without the conventional speakerís excess baggage there are no voice coils, cones, crossover networks, or enclosures. The result is concert-hall sound of a purity and fidelity never before attained.
Sound quality is no longer tied to speaker size. The HyperSonic Sound system intends to replaces inefficient conventional speakers wherever they are used: in the home, in movie theaters, in automobiles everywhere.
A Brief Look at Loudspeakers
About a half-dozen commonly used speaker types are in general use today. They range from piezoelectric tweeters that attempt to recreate the high end of the audio spectrum, to mid-range speakers to woofers that produce the lower frequencies. Although many speakers are capable of reaching 20,000 Hz, none regardless of cost can really operate at 20 Hz.
Even sophisticated hi-fi speakers have a difficult time with bass, and generally rely on a large woofer/enclosure combination to assist in the task. Whether they be dynamic, electrostatic, or some other transducer-based design, all loudspeakers today have one thing in common: they are direct radiating they are fundamentally a piston-like device designed to directly pump air molecules into motion to create the audible sound waves we hear. HSS technology produces sound in the air indirectly as a by-product of some other process.
Acoustical engineers and loudspeaker designers have struggled for nearly a century to produce a speaker design with the 20 Hz to 20,000 Hz capability of human hearing. Needless to say, they have been unsuccessful.
As electronics have advanced and speaker technology has been pushed to its limits, a whole array of terms have come to define the various forms of conventional speaker distortion: amplitude distortion, harmonic distortion, intermodulation distortion, phase distortion, crossover distortion, cone resonance, and so forth.
Every form of distortion contributed by a loudspeaker is traceable to some aspect of its mechanical nature: mass, magnetic structure, enclosure design, cone construction, etc. All form an important part of the final productís capability to perform its function in as perfect a manner as possible.
Speaker cone motion is subject to the laws of physics. This all-important element, more than any other in a speaker system, affects the overall purity of sound and can be a source of various forms of distortion. Ideally, when reproducing sound, the speaker cone should follow precisely the delicate nuances of any electrical waveform presented to it. The cone or radiating surface of a perfect loudspeaker would have virtually no mass nor resonances over the entire range of hearing, and would offer perfect linearity while at the same time being able to couple enough energy into the air to produce any sound level desired.
HyperSonic Sound technology does precisely that it provides linear frequency response with almost none of the forms of distortion associated with conventional speakers. Physical size no longer defines fidelity. The faithful reproduction of sound is freed from bulky enclosures. There are no magnets, crossovers, woofers, tweeters or bulky enclosures, nor are there any delicate electrostatic elements.
HSS fundamentally works by emitting a beam of high frequency ultrasonic energy which is converted to an audible acoustic wave in mid-air. An important by-product of the technique is that sound may be directed to just about any desired point in the listening environment. This provides outstanding flexibility, while allowing an unprecedented manipulation of the soundís source point.
It helps to visualize the traditional loudspeaker as a bare light bulb, and HSS technology as a flashlight. As with the light bulb, a traditional loudspeaker radiates sound in all directions. A listener can stand anywhere in an acoustical environment and point to the speaker as the source of the sound. HSS technology is much more analogous to the beam of light from a flashlight. If you stand to the side or behind the light, you can only see the light when it strikes a surface. HSS technology is similar in that you can direct the ultrasonic emitter toward a hard surface, a wall for example, and the listener perceives the sound as coming from the spot on the wall. The listener does not perceive the sound as emanating from the face of the transducer, only from the reflection off the wall.
However, look directly into the lens of a flashlight and you will see the highest intensity of light and it will appear to emanate from the face of the flashlight. If you direct an HSS ultrasonic emitter directly towards a listener, the listener will perceive the sound as emanating directly from the face of the emitter. In fact, the sonic sound waves are being created all along the ultrasonic wave in front of the emitter. A by-product of this ability to ìbeamî the sound is to tightly control the dispersion and project the sound to much further distances than conventional loudspeakers.
Dispersion of the audio wavefront can be tightly controlled by contouring the face of the HSS ultrasonic emitter. For example, a very narrow wavefront might be developed for use on the face of a computer screen while a home theater system might require a wider wavefront to envelop multiple listeners.
Range of Hearing
Compared to the human ear, even todayís highest technology loudspeaker is a very inadequate device. The human ear is sensitive to frequencies from 20 Hz to 20,000 Hz (the ìaudioî range), and can detect the vibration amplitudes that are comparable in size to a hydrogen atom.
If the range of human hearing is considered as a percentage of the progression from the lowest audible frequency to the highest, it represents a shift of 100,000%. No single loudspeaker can operate efficiently or uniformly over this range of frequencies. We must split the audio spectrum into smaller sections. This requires multiple transducers and crossovers to create a ëhigh-fidelityí system with current technology.
If the range of frequencies we can hear could be superimposed on a much higher frequency ìcarrierî such as 200 kHz, the required frequency shift for a single transducer would be only 10%. Building a transducer that only has to produce audio uniformly over a 10% frequency shift would be simple. For example, if a loudspeaker only needed to operate from 1000 to 1100 Hz (10%), an almost perfect transducer could be designed.
If the audio spectrum could be superimposed on this high frequency carrier and emitted into the air as an ultrasonic acoustical wavefront, the only thing remaining would be to ìdown convertî the ultrasonic energy to sonic energy we could hear.
Non-Linearity of Air
When two sound sources are positioned relatively closely together and are of a sufficiently high amplitude, two new tones appear: one lower than either of the two original ones and a second one which is higher than the original two.
There are now four tones where before there were only two. It can be demonstrated mathematically that the two new tones correspond to the sum and the difference of the two original ones, which we refer to as combination tones.
For example, if you were to emit 200,000 Hz and 201,000 Hz into the air, with sufficient energy to produce a sum and difference tone, you would produce the sum - 401,000 Hz - and the difference - 1,000 Hz, which is in the range of human hearing.
The HSS concept originates from this theory of combination tones, a phenomenon known in music for the past 200 years as ìTartini tones. It was long believed that Tartini Tones were a form of beats because their frequency equals the calculated beat frequency. However, it was Hermann von Helmholtz (1821-1894) who completely re-ordered the thinking on these tones. By reporting that he could also hear summation tones (whose frequency was the sum rather than the difference of the two fundamental tones) Helmholtz demonstrated that the phenomenon had to result from a non-linearity. Could a method be found today to utilize this non-linearity of air molecules in a manner similar to the non-linearity of an electronic mixer circuit?
In theory, the principle appears quite simple. Yet, until now, no one has succeeded in making it work. Nobody has been successful in producing useful levels of sound output in this difference frequency range.
Heterodyning Air
Although air is far from being an electrical signal, air molecules behave non-linearly (which allows mixing), as the amplitude increases. This is why, mathematically, HSS technology is generally similar to heterodyning in electronics. In a radio receiver, two electrical signals are mixed in such a way as to produce sum and difference frequencies. Virtually every receiver in the world, whether radio, TV, or cellular phone, uses this technique. Thus, the HSS system can be considered as a form of heterodyning acoustical heterodyning in that the creation of difference frequencies from other higher energy waves also takes place.
In air, the effect works in such a way that if an ultrasonic carrier is increased in amplitude, a difference frequency is created. Concurrently, the unused sum frequency actually diminishes in loudness as the carrierís frequency increases. In other words, the major portion of the ultrasonic energy transfers to the difference frequency which is what we can hear. The laws of physics have been kind to us here.
How HSS Works
HyperSonic Sound technology utilizes a custom-designed, ultrasonic emitter, that is capable of operating over a frequency range of at least 10%; therefore, if the carrier were 200,000 Hz, a 20,000-Hz upward swing from that point would create the entire audible range of hearing. The emitter is made up of a specially constructed piezoelectric material, mated to a unique acoustical interface. Several transducer designs are proprietary to ATC. Other emitter types will be made available by ATC as future applications require. Each of these various emitters will be quite small in comparison to existing speakers.
This specially constructed ultrasonic emitter produces a ìHyperSonicî
energy wave, custom-generated by proprietary electronics, with the proper
characteristics to cause the difference frequencies to become audible. The
high level of energy in the ultrasonic wave actually causes air molecules
within the ultrasonic wave column to vibrate at the difference frequencies,
causing a sonic (audible) wavefront to be produced all along the ultrasonic
column.
Efficiency
Traditional loudspeakers convert electrical energy into acoustical energy at an efficiency of approximately 0.25% - 0.50%. Electrostatic speakers operate at approximately .1% efficiency. A large portion of this inefficiency is caused by the mismatch of the acoustical impedance of air with the impedance of the loudspeaker cone material. Air has an acoustical impedance of .0004 MegaRayls (named after the British physicist Lord Rayleigh). The typical loudspeaker has between 1.5 and 2.0 MegaRayls of acoustical impedance. The acoustical impedance of the HSS ultrasonic emitter is much closer to that of air, providing an overall system efficiency expected to be approximately 10.0%.
Small Size
Not only has the conventional speakerís crossover network and enclosure been eliminated, but HSSí ultra-small radiating ultrasonic emitter is so small and light-weight that the inertial considerations ordinarily associated with traditional direct-radiation speakers are virtually non-existent. (And so is just about everything else associated with the conventional speaker: the voice coil and support structure normally used to attach the moving cone in place.)
Point Source
The ability to produce the entire audible spectrum of frequencies from a single point source has been the goal of transducer engineers for the past 50 years. The improvement in phase response, time alignment, and frequency response becomes obvious.
What About Performance?
Preliminary testing of the ATC proof-of-concept prototype shows the HSS technology should have the potential for the following performance specifications:
What about our animal friends?
In reality, sound waves have a relatively small energy content. For instance, if every man, woman, and child in New York City spoke loudly at the same time, the total acoustical energy produced would barely brew a single cup of coffee.
The most familiar applications for ultrasonics today are in the medical field, and do not generally involve radiating into the air. More commonly, ultrasound is used to image the brain and other organs. The most familiar application of ultrasonic waves is the sonogram, an imaging device used regularly in the prenatal treatment of pregnant women to monitor fetal development. Interestingly, it was Elwood Norris who, years ago, developed one of the core technologies that later evolved into the sonogram.
More recently, ultrasound is also being used to speed the healing process of bone fractures and other injuries. Abundant data in medical literature validates the fact that ultrasound at these frequencies is harmless. There is no need to worry about pets, either. Dogs and cats can hear sounds up to perhaps 40,000 Hz, and HSS operates well above this range.
Applications for HSS
HSS technology applications are limited only by the imagination High volume applications are numerous and include:
Besides consumer electronics, the entertainment industry is expected to be fundamentally influenced by this development. In a movie theater, sound can be made to emanate directly from an actorís mouth on the screen. Special effects will no longer be limited to the capability of loudspeakers positioned around the auditorium.
You might want to project concert sound throughout an audience instead of using huge speaker stacks in front. A small table radio might project sound around an entire room. Why not equip your back yard with tightly focused HSS emitters to project sound all around your yard for that next pool party.
Until now, it has been difficult for a hearing aid regardless of price to reproduce the entire audio spectrum. This no longer need be the case. With HSS, hearing aids may also shrink further in size.
Virtual reality, in large-scale applications, has been brought another step closer.
No longer is the quality of the sound related to the size or type of a speakerís enclosure. Everywhere and anywhere a speaker is in use today ships, aircraft, hospitals, automobiles the HSS technology can replace the bulkier, inefficient speakers, and provide far better results than we have ever heard.
Truly, this is a quantum leap, a paradigm shift.
Implementation
American Technology Corporation has established a strong portfolio of pending patents covering every aspect of HSS technology and intends to license HSS on a non-exclusive basis to manufacturers of products requiring the reproduction of sound. ATC will provide a commercial source for HSS Ultrasonic Emitters and the DSP Pre-Processing required to develop the proprietary HSS ultrasonic wave along with the superimposed audio.
Another byproduct of HSS technology is the super-high impedance of the
ultrasonic emitters. Power amplifier stages can now be engineered without
the requirement to produce high current, making them cheaper, lighter-weight,
and less bulky.
Potential implementation for monaural applications:
Potential implementation for stereo applications:
Potential implementation for computers:
Potential implementation for 5.1 home theater applications:
