Air Velocity Transformer: Is This A Solid Theory?

For all you speaker designers out there is Dr. Heil on to something with this transducer design or is this just another in a long line of different ways to skin the same cat? Any thoughts on the following information? Has anyone heard these speakers?

OSKAR A.V.T. - Air Velocity Transformer

"Dr. Oskar Heil, noted physisist and inventor of the Field Effect Transistor, began his research into loudspeaker design, not with abstract theory of how a loudspeaker should work, but with a study of the peculiarities of the human listening aparatus. The result of this intensive year-long research program led to his discovery of the principle on which the Oskar Air Velocity Transformer is based. By applying this principle to the design of a loudspeaker diaphragm, he was able to achieve a revolutionary breakthrough in solving the fundamental problems of diaphragm mass, inertia and self resonance. In the following, we describe the results of Dr. Heils research and how it led to the development of the Heil Air Motion Transformer speaker.

The research behind the Oskar A.V.T. As a physicist, Dr. Heil concentrated his study on how nature designed and constructed the human ears. Then his studies concentrated on animals of a small proportion, which can produce a loud sound, especially compared to their size. These studies led to Dr. Heil's formulation of his basic diaphragm design theory and the subsequent development of the Oskar A.V.T. (AMT) Air Velocity Transformer.

How the A.V.T. (AMT) operates: The unique design feature of the OSKAR A.V.T. (AMT) which distinguishes it from all other speakers is an extremely lightweight diaphragm, folded into a number of accordion-like pleats to which aluminium foil strips are bonded. The Diaphragm is mounted in an intense magnetic field and a music signal is applied to the aluminum strips. This causes the pleats to alternately expand and contract in a bellows-like manner in conformance with the music signal forcing air out of the pleats and sucking in on the other side, the air movement is 5 times bigger than the movement of the membrane, therefore also the velocity must be 5 times bigger.The total moving mass is approx. 1 gram, we have therefore an almost perfect transducer system. The A.V.T. (AMT) multiplies (transforms) the air motion by a factor of 5.3 (with a total mass of less than 1 gram) and is, therefore, appropriately called an "AIR VELOCITY TRANSFORMER".

Ability to differentiate sounds: A principal function of the ear is to identify voices and for this it has developed an extraordinary ability to differentiate sounds. Single sound sources, such as a distant voice can be separated from other sounds by concentrating our hearing apparatus upon the voice and ignore noise or other voices which we do not want to hear.

Volume (Intensity) variations: The ear has little sensitivity to sound level "jumps" or to the relative loudness of different sound's which are audible at the same time. For a loudspeaker, sound output levels (amplitude) over a range of frequencies are valid criteria, but are of less importance for our ears. Our ears are protected from damage by a construction which makes them relatively insensitive to amplitude changes. The difference in amplitude between a whisper and normal volume speech is not just 1:2 or 1:4, but 1:100'000.The relative loudness of different sounds, within certain limits, is therefore not too important to us, since the ear has the ability to adjust to different levels. This explains why street noises do not necessarily disturb conversation level. It also explains why we can hear an opera singer even though the sound level of the orchestra is many times that of the voice itself.

Frequency variations: In contrast to its relative insensitivity to amplitude variations, the ear is extremely sensitive to minute fluctuations in the frequency of sounds, especially in the mid. frequency range. a half-tone in the musical scale represents a frequency change of 6% while the frequency shift in the vibrato of a violin is approximately 0.5%. In the critical midrange of 250 - 6000 Hz, we can differentiate between two tones even when the frequency difference is as little as 0.06%.

It is this sensitivity to frequency variations that enable us to identify different voices. When we speak, we do not produce constant tones, but tones which are constantly varying. We can usually recognize a familiar voice immediately even over the telephone and can often tell the mood of the other party by the differences in speech pattern produced by the changing of the tension of his vocal cords.

Frequency variations verses amplitude variations: It is commonly accepted that the smallest change in amplitude that the ear can detect is 1 dB, which is a power difference of 26%. Compared to the ear's sensitivity to frequency variations of 0.06%. Contrasting to this relative insensitivity to amplitude changes with the ear's extreme sensitivity to frequency variations, it is difficult to understand the loudspeaker industry's obsession with the minor loudness variations of 1 or 2 dB in the frequency response of a loudspeaker, while completely ignoring the audible shifting or fluttering or high frequencies which can result from changes in membrane stiffness as a sound wave spreads transversely across a diaphragm.

Phase Differences: The Ability to Localize Sounds A listener's ability to localize sounds is made possible by phase differences ( time delays) resulting from the difference in path lengths from a sound source to each ear. This ability is frequency dependent and is more pronounced in the critical range of 500 - 3000 Hz. than at lower and higher frequencies. This is why the speed of response of a loudspeaker diaphragm is extremely important to the faithful and realistic reproduction of music. If the loudspeakers diaphragm cannot respond fast enough to enable it to reproduce these transients, or if it distorts them, the listener's ability to recognize and localize the sound source is greatly diminished and the realism of music reproduction and the pleasure of listening is seriously reduced.

Problems of loudspeaker design
Spurious diaphragm resonances: Any solid material which is made to vibrate by striking it or otherwise setting it in motion will produce a unique pattern of resonances characteristic of that particular material. If made to vibrate at a specific frequency by an external driving force it will, in addition to this frequency introduce its own resonances. In music, the pattern of these resonances or harmonics is peculiar to each instrument and enables us to distinguish between the sound of a saxophone (metal), for example, and an oboe (wood) even though both instruments are playing the same fundamental note. This characteristic, useful in recognizing musical instruments, constitute a major problem for the loudspeaker designer, since spurious resonances generated by a diaphragm will distort and mask the musical signal. In order to move a large amount of air with minimum loss and provide fast response to the transients, the diaphragm must be extremely lightweight. However, if the diaphragm material is too thin and light, it will not be sufficiently rigid to prevent it from flexing and producing its own resonances. If the deformation occurs between the center area and the edges, that portion will vibrate independently of the music signal and produce standing waves or bell shaped vibrations which are clearly audible as distortion. In addition, the diaphragm will store the resonant energy and, when the music signal stops, it will continue to move in order to dissipate this energy. The continued vibration of the diaphragm will dampen (absorb) the sharp rising transients of the following music and seriously affect the quality of the music reproduction.

Efforts to Eliminate Unwanted resonances: Attempts by designers to minimize diaphragm resonances usually consists of coating the diaphragm with silicon rubber or other substances (this is called dampening) to increase its rigidity and prevent it from flexing. There is a trade-off, however, while the damping material may help to reduce resonances, it adds to the weight of the diaphragm increasing its inertia and resulting in a slower speed of response to the transients of complex musical wave forms. The ability of the diaphragm to move air efficiently is also reduced on many loudspeakers to a mere 0.25%.

Large diaphragms and differentiated driving force. Efforts have been made to minimize unwanted diaphragm resonance by applying the driving force more evenly over a large area of the diaphragm. Electrostatic speakers distribute the driving force over a large, flexible plastic panel suspended on a framework. EMIT and magnetostatic speakers utilize a differentiated driving force applied to different areas of the diaphragm to compensate for the varying flexibility of its surface. However, when a flat or conical diaphragm supported at its edges is caused to vibrate only part of the diaphragm oscillates in a direction perpendicular to its surface. At the outer edges, where it is suspended, it cannot oscillate in the same manner since the surface of one side will stretch with each + sinus oscillation, while the reverse side will be compressed or "crunched" and vice versa. Thus the entire diaphragm will not move uniformly like a rigid piston, but will vibrate like a suspended flexible membrane and produce a self resonance with a pitch. (singing saw effect)

The OSKAR A.V.T. Kithara

Read an online review from:

Speaker elements: 1 A.M.T. mid range - tweeter 700 - 23000 Hz , 1 25 cm bass unit 28-700 Hz.
Total Frequency response: 28-23000 Hz +- 5 dB Sensitivity: 94 dB 1 W 1 meter
Sensitivity: 94 dB 1 W, 1 Meter
Amplification Requirements: 50 - 200 W
System Type: Bass reflex
Impedance: 4 ohm minimum
Cabinet finish: Oiled walnut, cherry, or black, maple wood veneer
Dimension W/D/H: 40 x 40 x 110 cm including A.M.T.
Weight: 35 Kg.

Oskar A.V.T. ( AMT) Aulos

Read an online review from:

Speaker Elements: 1 A.M.T. mid range tweeter 1500 - 23000 Hz 1 15 cm bass unit 40 - 1500 Hz
Total Frequency Response: 40 - 23000 Hz
Sensitivity: 89 dB 1 W 1 meter
Amplification Requirements: 50 - 200 W
System Type: Bass reflex
Impedance: 4 ohm minimum
Cabinet finish: Oiled walnut, cherry or black maple veneer
Dimension including grill W/D/H: 23 x 30 x 50 cm
Weight: 8.7 Kg."
Yes, the theory is sound. In addition to Oskar, Elac also produces an AVT devise based on Dr Heil's original design called the JET. There is both information and reviews on their site.
I have a pair of ESS AMT 1 Towers, that are almost 30 years old. They use the Heil for the frequencies above 800 hz. In all of these years, I have yet to hear a transducer that does highs and especially transients better than the Heil. The 10" woofer is another story. It is somewhat adequate, but pales in performance to the tweeter. I am now in the process of trying to replace the old woofer with something that will sound better in the original enclosure. I am also planning to build a bi-amped speaker system, using the Heil, for the highs, and a powered sub. I have just purchased, and received a pair of mid-woofers, that I will be experimenting with to find a proper match. It's hard to be satisfied with ordinary speakers, once you've heard the Heils.
I have not yet heard the Kitharas. If my effort proves to be unsatisfactory, then I would like to give them a listen. Until I hear better, there will always be a Heil in my system. Sonny
Anyone interested in the Heil drivers must check out Adam Audio speakers. They use a version of the Heil for the tweeter...PLUS they have a separate Heil-type driver for the midrange (!) they use what seem to be excellent Hexacone woofers.
I heard both the Oskar and Adam loudspeakers at T.H.E. Show 2004 at the St. Tropez. In the Oskar AVT line, I much prefer the Khitaras over the Syrinxes. The Khitaras give a smooth, wide soundstage with extended highs. In the Adam A.R.T. line, I heard the Pencils, the Center and the Compacts in a multi-channel set-up. The sound while being transparent and seamless is more noted for its alive and dynamic character. These speakers can play really loud. The fascia of the Adam loudspeakers have changed. There is now a thick aluminum face plate on top of the front baffle where the drivers are situated. I took pictures of these.
Gaudio_eek-> can you post the pictures of the adam Art line?
Oops, my apology. I just looked at the 150 pictures I took from CES and T.H.E. Show and the Adam Audio Loudspeakers pictures are not there! I must have enjoyed the sound so much that I thought I have taken them. The good news is I carried the color prospectus back with me. I can have it scanned in color and share it with you. IMHO, these are incredible speakers at competitive retail prices.
The Heil room stunned many listeners at T.H.E. SHOW in Las Vegas. Many audio “luminaries” practically camped out in the room enjoying the performance. The Heil is a great speaker but you must remember these demonstration rooms are a package deal. If you were there you would have seen two signs on the wall between the speakers: Diva and Sahuaro Audio Cabling. Both of these companies played a major roll in the overall presentation. As one reviewer put it, “This is the best I have ever heard the Heils; and we all know this would not be case without Sahuaro Cables in the system”. The first two trial assemblies before the show started were conducted with electronics other than Diva and were rejected once Diva was auditioned.
I failed to mention the speaker version we were using was the OSKAR A.V.T. Kithara.
I enjoyed both the Heil room and the Adam room. I hope these products get some momentum.
Thanks, I am glad you enjoyed the rooms.