research behind the Oskar A.V.T. ( AMT)
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. Heils formulation of his basic diaphragm design theory and the subsequent development of the Oskar A.V.T. ( AMT) Air Velocity Transformer.
|Spurious Diaphragm resonances:The design of the Oskar A.V.T. ( AMT) diaphragms makes the use of dampening material with all of its detrimental effects, totally unnecessary|
|Non Uniformity of Driving force: In the Oskar A.V.T. ( AMT), the driving force is applied uniformly over the entire surface of a structurally rigid diaphragm by means of the conductive aluminium foil strips.|
|Ability to move air efficiently: The A.V.T. ( AMT) diaphragms pleats propel air at a speed of 5.3 times their own velocity.Oskar Heil AVT/AMT|
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
-------airconditioner noise - - - - desired information
noise as discriminated by the ear is always below the level of the desired information.
( Intensity) variations. The ear has little sensitivity to sound level
"jumps" or to the relative loudness of different sounds
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 1:100000.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 speechpattern 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 ears sensitivity to frequency variations of 0.06%. Contrasting this relative insensitivity to amplitude changes with the ears extreme sensitivity to frequency variations, it is difficult to understand the loudspeaker industrys 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 listeners 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 extremly 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 listeners 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|
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 charactristic, 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
point of energy: ( flaps)
dual point of energy ( reduces flapping)
energy applied over the surface, (no flapping)
|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%||
diaphragms and differentiated driving force. Efforts have been made
to minimize unwanted diaphragm resonances by applying the driving force
more evenly over a large area of the diaphragm.
EMIT and magnetostatic speakers utillize 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 uniformely like a rigid piston, but will vibrate like a suspended flexible membrane and produce a self resonance with a pitch. (singing saw effect)
Heil A.M.T. actual membrane
the way the membrane works
Large diaphragms and differentiated driving force. Efforts have been made to minimize unwanted diaphragm resonances 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 utillize a differentiated driving force applied to different areas of the diaphragm
Spurious Diaphragm resonances:The design of the Oskar A.V.T. ( AMT) diaphragms makes the use of dampening material with all of its detrimental effects, totally unnecessary.
Non Uniformity of Driving force: In the Oskar A.V.T. ( AMT), the driving force is applied uniformly over the entire surface of a structurally rigid diaphragm by means of the conductive aluminium foil strips.
Ability to move air efficiently: The A.V.T. ( AMT) diaphragms pleats propel air at a speed of 5.3 times their own velocity.Oskar Heil AVT/AMT
How the OSKAR A.V.T. operates.
| The unique
design feature of the OSKAR A.V.T. which distinguishes it from all other
speakers is an extremely lightweight diaphragm, folded into a number of
accordeon-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 under pressure out of the pleats and sucking the air in on the other side, the airmovement is 5 times bigger than the movement of the membrane, therefore also the velocity must be 5 time bigger.The total moving mass is approx. 1 gram, we have therefore an almost perfect transducer system. This principle can be demonstrated very simply by taking a sheet of DIN A 4 paper with a surface of 616 cm2, folding it in the center lengthwise and bending the long edges together to form an opening of 5 cm on the one side. We imagine, that the upper and lower part of the structure is closed and move each side 2.5 cm together. With a frontal surface of 140 cm2, we have now moved 770 ccm of air, compared with the 350 ccm of air moved by a flat diaphragm. Our transformation is now 1:2.2, by making the triangle (top view) a square form, we doubled the transformation to 1:4.4 The selected transformation ratio with the Oskar A.V.T. is 1:5.3.
Unlike conventional speakers, whos diaphragms move air only in a direct proportion to their own movement with the inherent inertia. The A.V.T. multiplies (transforms) the Air Velocity by a factor of 5.3 (with a total mass of less than 1 gramm) and is, therefore, appropriately called an AIR VELOCITY TRANSFORMER.