SunAge,
Thanks for the correct http.
I have had a study done about the ATCO Speakerless sound reproduction.
There are some very dangerous elements to be considered. The possible health hazards are real!
Study the following report.
humble carl
------------------report follows------------------------------------
Analysis of American Technology Corp.
As you have requested, I have reviewed the "HyperSonic" speaker technology promoted by American Technology Corp. My information sources are the public records provided by the company and interviews of those who have seen and heard the prototype.
THE CLAIMS
From the publicly available information ATC has described "HyperSonic" Sound with phrases such as:
1. Speakerless sound reproduction
2. An entirely new method of sound reproduction
3. Sound is literally generated in air directly, without need for loudspeakers, by inaudible ultrasonic waves that interact in space to produce audible sound.
4. We are demonstrating previously unknown techniques
5. Compatible with existing audio recording and broadcasting techniques
6. Uses none of the elements of traditional loudspeakers
7. Sound quality is no longer tied to speaker size
8. We have the ability to manipulate the apparent point source of sound
8. A compelling alternative to conventional loudspeakers
9. Has applications in multimedia, cinema, stadiums, concert halls, telephone headsets, answering machines....
10. A radically different approach to reproducing sound
11. The method avoids the distortion produced by traditional loudspeaker components
12. This method of sound reproduction eliminates the imprecise cones in conventional loudspeakers
13. Represents a quantum leap in technology
14. The phenomenon known as combination tones or the existence of difference and summation tones has been observed since the middle of the eighteenth century, but to date no one has made practical use of these concepts.
15. Produce virtually perfect sound production across the audio spectrum and beyond
16. Provides ultra-wide dynamic range and ulta-wide frequency response without distortion
17. A highly efficient converter of electrical energy to acoustical energy
18. Sound quality is no longer tied to speaker size.
ANALYSIS OF THE CLAIMS
The claims may be grouped as follows:
1. It's new.
It's not.
Acoustics is a well understood engineering discipline. Ultrasonics is a well understood engineering discipline. Heterodynes are well understood. Any wave phenomenon, sound, radio, optical, or even ocean will produce heterodynes in the presence of a something with a nonlinear transfer characteristic.
Every superheterodyne receiver uses a local oscillator and heterodynes to generate the IF frequency. Ultrasonic heterodynes producing sum and difference frequencies are a well known phenomenon in sonar design. Millions of burglar alarms use ultrasonic transducers. Polaroid cameras even use a variation of ultrasonic heterodynes to focus its cameras.
2. Its not a speaker.
It is.
Any sound must be generated by compressing air molecules. The more molecules you compress and the
harder you compress them, the louder the sound. HSS compresses the air molecules with the mechanical diaphrams of little bitty ultrasonic transducers, precisely the same sound production mechanism used by everything from crystal earphones to boom-box stereos.
3. It's science.
HSS is in fact science, and that is precisely its problem.
ATC claims that HSS is based on well-known physics principles. From Physics 101,
"In a closed system, energy must be conserved."
In other words, you cannot get more energy out than you put in.
The resulting HSS sound, regardless of what transformation it goes through in the air or bouncing off walls, cannot possess more energy than that imparted by those little bitty ultrasonic transducers.
4. It's better
It's not.
The reasons are many, and probably include a few others::
a. Commonly available consumer ultrasonic transducers such as those possibly used in the prototype generate milliwatts of power not the tens or hundreds of watts necessary for high-fidelity sound reproduction.
b. The human ear is about 10% as sensitive to bass sounds as midrange. These are the sounds
that are the most challenging for speaker manufacturers to reproduce, and precisely the sounds that HSS is least equipped to handle.
c. Production ultrasonic transducers are designed for single frequency operation and are
very high Q. (Frequency response is lousy.)
d. Ultrasound attenuates rapidly in air. (The air absorbs the sound.)
In order to have 1 watt of power present at 20 feet, a 200khz HSS system must radiate 1,000 watts. (See f. below)
e. Ultrasonic amplifiers are harder to design. HSS will require driver electronics to operate significantly above the 20-20,000Hz range of audible reproduction. Any amplifier has a speed/power product which determines its frequency response and the amount of power output.
This means that if you double the frequency, you halve the available power. By going from 20khz to 200khz an amplifier will have one tenth as much power available.
Much of the available power in high-fidelity amplifiers is used in negative feedback to correct for distortion.
If power is diverted away from negative feedback, distortion will increase. A class A amplifier running without negative feedback can produce distortion in the 5% -7% range. This is very low-fidelity.
f. **************************** IMPORTANT ********************************
ATC is apparently aware of the power problem and is building a new prototype. In order to overcome the power and attenuation problems, they may be tempted to build powerful drivers and couple them to powerful ultrasonic transducers. The technology exists to build 1KW ultrasonic systems. They are expensive, and they are called ultrasonic welders.
Such a system could be incorporated into an HSS speaker. A 200 khz HSS speaker will dissipate most of its energy in air friction within six feet of the radiator. This means the area in front of a 1KW "HyperSonic" speaker will be similar to sitting in a microwave.
It's going to get really hot.
This is a substantial health risk, particularly for small children. There is no indication from the public documents that anyone at ATC appears to have the slightest clue of this potentially life threatening risk.
g. Ultrasound tends to form beams and ultrasonic transducers sort of look like point sources. Orchestras in concert halls are not point sources. The speakers that reproduce them had better not be either.
h. Ultrasonic beams tend to diffract (bend) around objects. Every chair, bookcase, or pencil sharpener in a room could look like a source and produce the effect of sitting in a poorly designed concert hall.
5. True but it's a negative.
ATC claims the ability to manipulate the apparent point source of the sound. This is in fact true and is an artifact of ultrasonic waves tending to form into beams. This is how sonar works.
It is also the same phenomenon which causes tweeter dead spots in poorly designed high-fidelity speaker systems.
OTHER OBSERVATIONS
Sound Reproduction
Sound reproduction is the imparting of a physical disturbance pattern in the elastic medium of air. To make louder sound, move more air. ATC claims that they make sound out of thin air. This is not true. Their ultrasonic transducers have vibrating surfaces just like any speaker. The audible difference frequency is probably not produced by nonlinearities in the air but rather by nonlinearities in the ultrasonic transducers themselves, room walls, or possibly by individuals' eardrums. There is no public information to indicate ATC has done any research or has the capability to do any research to determine which of these four is in fact the nonlinear mechanism required to produce any audible difference frequency.
In any case, you can get no more energy out of a system than you put in. Regardless of the mechanism of sound reproduction, the ATC transducers will be able to produce no more audible energy than they the ultrasonic energy they radiate. The amount of energy they are currently able to radiate is very small.
The Walkman Test
Walkman headphones are really little speakers. These tiny transducers have a very wide frequency response and reproduce solid bass notes. However, they have very little ability to move large air masses due to the small size of their diaphrams.
If you hold the headphones next to your ear, the sound will be outstanding. I you hold the headphones away from your ear the bass notes will disappear. HSS as implemented with the little bitty ultrasonic transducers has the same problem. These transducers do not have enough diaphram area to move enough air to generate much volume, particularly bass notes.
The Attenuation Problem
Attenuate means to weaken. Accoustic waves propagate though air by making the molecules bump against one another. Each bump consumes a little energy due to friction and weakens the sound wave. Just like the friction brakes in a car, the friction with air molecules will transform energy into heat. Higher frequency accoustic waves require the molecules to bump back and forth faster, thereby wasting more energy and producing more heat.
Ultrasonic signals vanish within very short distances. A 200 khz accoustic wave will possess only 1/1,000 of its energy after traveling only 20 feet. If HSS is generating the 200 khz accounstic waves they claim moving a few inches in either direction could cause the signal to essentially disappear.
The Unknown Medical Implications
If ATC is operating at 200khz as claimed, in order to make 1 watt of power available 20 feet from the "HyperSonic"speaker, they would have to radiate 1,000 watts of power. An individual walking too close to the "HyperSonic" speaker could in theory instantly destroy their auditory nerves.
We know absolutely that such high power ultrasound will generate a lot of heat which is in itself dangerous. The government has done some research on the use of high frequency sound as a weapon to incapacitate enemy soldiers. Most of this research is classified. I do not know the effects of high intensity ultrasound on human
soft tissue, but I would be particularly concerned about the sense organs and nerves.
Effects of Diffraction
Diffraction is the bending of any wave around any physical obstical. The bending increases as frequency increases. At high ultrasonic frequencies the wavefront is likely to be diffracted by objects such as furniture, fixtures, and even people.
Human Ear Sensitivity
Depending on the intensity of the signal, the human ear is as much as 100 times less sensitive to a 50 Hz tone as it is to a 5Khz one. For a high fidelity speaker system, this means much more energy is required to produce a bass signal of the same loudness as for a midrange signal. Any "hypersonic" speaker will be at a great disadvantage producing any perceptible bass notes.
The "Hypersonic" Speaker Prototype
The prototype appeared to be made from an array of approximately 20 ultrasonic transducers similar to those found in consumer burglar alarms. The operating frequency of these devices is in the range of 30khz rather than the 200 Khz claimed by ATC. They are also commonly available from surplus electronic outlets for about $2.00. Each unit can be driven by several milliwats. Twenty of them would produce a sound volume similar to that of an AM radio. This is consistent with the reported performance of the prototype.
I have been unable to locate any commercially available 200 Khz ultrasonic transducers for air. Sonar transducers are available in that range but would not radiate into air. Ultrasonic transducers for medical imaging devices work at the higher frequencies, but the accoustic wave is propagating through fluid and soft tissue rather than air and has more in common with sonar technology than air acoustics.
The Unasked Question, "Why Ultrasonic?"
In almost every technical venture there is a compelling reason why the technology is superior to the existing art. CD audio is superior to records because digital signals can easily be corrected to near perfection and analog signals cannot. CMOS logic is superior to NMOS computer logic because CMOS can pull signals both directions instead of one, and power is only consumed during switching. Jet aircraft can fly faster than propeller aircraft because propellers lose efficiency when the tips run at supersonic velocities.
There is no apparent advantage to indirectly producing audible accoustic waves from ultrasonic transducers over directly moving the air with conventional speakers. There appear to be numerous disadvantages.
No where is there any evidence that an engineer sat down with pencil and paper and asked, "How can I produce better sound."
Marketing
It is not clear why ATC has decided that "hypersonic" speakers are necessarily suited to high fidelity sound reproduction. There is no compelling mathematical argument. In fact, mathematical analysis argues for low fidelity rather than high.
The ability to generate sound from ultrasonic transducers is not new and it is not unique. Sound can be generated by everything from table salt to candle flames. They all can make sound, just not very well.
This is born out by the performance from the prototypes which is described as very AM radio-like.
It appears that ATC/Carver is targeting the ultra-high-end high-fidelity aficionado. If the speaker performs, even if it is expensive to make, this is a good niche to target. However, the aficionado market is very small, and the customers very particular. Some of these folks actually believe they can hear the difference gold plated cables make. They may buy something based on a good story alone if the product isn't noticeably inferior. They will not buy anything that is in the least bit substandard.
ATC has claimed that versions can be made to pipe sound into theaters and stadiums. Somebody at ATC clearly does not understand what happens to ultrasonic signals in air. Using the attenuation factors of a 200 khz sound wave propagating in 25 degree C 50% humidity air, to fill a football stadium with the equivalent sound intensity of current technology would require a driving energy of approximately 1.8 X 10 followed by 75 zeros watts. This is on the order of the power generated detonating a very very large thermonuclear device.
Patents
ATC states that "Hypersonic" speakers are patent pending. This in itself means nothing more than the company has submitted something to the Patent office and paid the $400 filing fee. Even an issued patent does not mean that the technology works. Rather it means than nobody has done it before.
Technical Expertise
I have been unable to locate any technical credentials on the inventor, other than he appears to be a high school graduate and a self-taught tinkerer. I have been unable to determine from the publicly available documents whether ATC has access to any other technical expertise. Ultrasonics is not an area for the technically shallow.
This is particularly true in light of the substantial health and safety risks. From the available public documents, the research effort can easily be compared to children playing with rocket fuel.
I will say it again. This is dangerous.
It does not appear that anyone associated with the company has the ability to perform the mathematical analysis necessary to figure out what is really going on.
From the public announcements, it appears that ATC may not really understand how the "hypersonic" speaker works or why it doesn't work. The technical hurdles to be cleared to produce high quality sound from ultrasonics are immense and may not be soluble by even those skilled in the art. The health risks are probably even more severe.
Conclusions
Personnel - From the public documents, there appears to be no one with accoustic, ultrasonic, or even electrical engineering expertise involved in the development of the technology.
Technical Merit - No mathematical analysis of the technology has produced a single piece of evidence why using ultrasonic transducers to produce audible sound should be lower distortion, higher frequency response, higher efficiency, or lower cost. In each area, the math argues for higher distortion, poorer frequency response, dramatically lower efficiency, and higher cost.
The math weighs mightily against the production of anything matching current reproduction systems, much less surpassing. The attenuation of ultrasonic signals in air and the necessary acceleration of air molecules to produce sounds are an immutable law of nature. They cannot be just willed away.
In addition, and most important, the potential health risks from this technology are significant. The speaker may not work, but let's not disable people in the process of trying to make it work.
This project reminds me of a design funded by the State of Louisiana which I reviewed . The gentleman had an electric motor which drove a hydraulic pump which drove a hydraulic motor which in turn drove the transmission of an automobile. He had convinced the bureacrats that he'd invented the world's most efficient car, but he couldn't get it to go faster than one or two miles per hour.
He didn't seem to understand that he couldn't get any more power out of the hydraulic motor than he put into the electric motor which drove the pump.
If you are seeking funding for ATC, I suggest you contact the Lousiana state offices in Baton Rouge.
Russell Fish III
Mr. Fish has a BSEE from Georgia Tech and an MSEE from Arizona State. He holds several patents in communications, computer peripherals, and CPU design. He is the author of "Microprocessors in Systems". His exploits from the early days of microprocessors are chronicled in Bill Davidow's book, "Marketing High Technology".
From time to time Mr. Fish evaluates business plans for investors and venture capitalists. Mr. Fish was also the 1989 Air Enduro World Skydiving champion.
He may be reached at rhfish@ix.netcom.com |
