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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
apparatus capable of forming audio signals (e.g. voice, music). In particular, the invention relates
to an apparatus for focusing and emitting an acoustic signal substantially in one direction.
Prior art systems in which the audio signal is radiated directly as an air vibration through the
individual loudspeakers or loudspeaker arrays can only achieve a relatively limited convergence
of the acoustic radiation. On the other hand, in the new method, the audio signal is not directly
output, but is output as amplitude change (amplitude modulation, AM) of the carrier signal of
very high frequency (ultrasound). The acoustical perception of the underlying physical
phenomena, ie chords and differences as a result of the non-linear character of air, has already
been recognized and studied by the 19th century physicist Helmholtz. It is published in
Yoneyama, Fujimoto, Kawamo & Sasabe "The audio spotlight: An application of nonlinear
interaction of sound waves to a new type of loudspeaker design", journal of the application of
this principle of physics to the structure of ultrasound / audio speakers. Acustic Society of
America, 1983, p. 1532-1536.
The ultrasound / audio speaker first forms a carrier signal at a frequency higher than the upper
limit of human hearing, ie, in the ultrasound range. The carrier signal is amplitude modulated by
the audio signal to be transmitted to form an audible sonic vibration. Since the ultrasonic carrier
signal itself can not be heard, it can be emitted with high sound pressure. At this high sound
pressure, the characteristics of the air are non-linear and thus act like a demodulator. The AM
signal is thereby demodulated and the audio signal is again formed in the audible area as air
vibrations. Since the audio audio signal is first generated in the medium air itself, its volume first
always increases with distance from the transmitter (ultrasound speaker) and then decreases
again as the poles become relatively large due to absorption of air. .
Here the spatial extent lateral to the illumination direction, or the convergence of the generated
audio signal, depends on the convergence of the ultrasound carrier signal (the opening angle of
the ultrasound cone cone to be illuminated). That is, it is slightly larger than the ultrasonic
region. This causes unwanted reflections at objects, especially when space is limited (vehicle
interior). It is also nearly impossible to acoustically limit only to special listeners (e.g. multiple
passengers of the vehicle select individual listening programs) because of the lateral spread of
the audio signal.
It is important in such modulated ultrasound signal based systems that a certain distance is
required to the transmitter in order to form an audible signal. This spacing is about 20 cm to 1 m
in an actual system. Thus, when used in tight spaces (vehicles), special technical problems occur
(such as maintaining a minimum distance between the ultrasound speakers and the listener,
adjusting the audio signal well to each listener, etc.) It can.
From DE 196 288 49 A1 a directional radiator equipped with a parabolic reflector is known, by
means of which it is possible to converge and emit towards the listener. For this purpose, the
emitters are directly oriented towards the listener.
A system is disclosed in DE 42 30 362 A1 which provides for the intended amplification of
partial areas within the total area. Here, an ultrasound carrier signal modulated by an audio
signal is emitted towards the listener via a group of loudspeakers.
A further disadvantage is that the ultrasound carrier signal has to be irradiated with high
intensity. This is because non-linear characteristics of air occur for the first time at a
correspondingly high sound pressure, which is necessary for the demodulation of the audio
signal. In an actual system, an ultrasound level of about 130 dB (A) is already required for small
to medium speakers to form an audio signal. On the other hand the usual levels for audible sound
waves (music, voice) are in the range of about 30 to 90 dB (A). The health effects of very high
ultrasound levels on humans have not yet been well studied. Even in vehicle use, high ultrasound
levels may sometimes cause undesired side effects, in which case several ultrasound transmitters
may be active at the same time to possibly form different audio signals for different passengers.
It may cause.
SUMMARY OF THE INVENTION It is an object of the present invention to improve the method
and apparatus for the directed irradiation of audio sound waves based on modulated ultrasound,
and for audio sound wave convergence, the required spacing between the transmitter and the
listener , And to overcome the aforementioned drawbacks with high ultrasound levels.
SUMMARY OF THE INVENTION The subject of the present invention is to use the reflector to
deflect an audio sound wave to a listener and to transmit the ultrasound carrier signal to the
listener prior to reaching the listener. The solution is by damping by means provided between
A corresponding device for carrying out the method of the invention is described in claim 7.
Further details and advantageous embodiments of the invention are given in the dependent
invention, an ultrasound signal whose amplitude is modulated by a conventional system is first
emitted from an ultrasound transmitter, where the ultrasound propagates in the form of a
focused acoustic cone.
FIG. 1 schematically shows this type of arrangement. The ultrasound transmitter 1 forms an
amplitude modulated carrier signal which propagates in the form of a focused ultrasound cone
cone 2. The high sound pressure in the ultrasound cone cone forms the audio signal 3 which is
likewise in the region of conical shape. The two sound cones reach the listener 4 spaced apart by
the transmitter. This interval is necessary for demodulation of the audio signal.
Usually, the carrier signal is strongly converged. That is, as shown in FIG. 2, the ultrasonic cone
has a relatively small aperture angle to the area of the audio sound wave. Here, the various
frequencies of the audible audio signal are generally focused at spatially different intensities. FIG.
2 shows this spatial distribution of sonication as a function of sonic frequency. Shown are
measurements at an ultrasound transmitter with a carrier signal frequency of 127 kHz, showing
two different frequencies of the audio signal demodulated in air. The dB value of the measured
power is shown in the Y direction and the illumination angle is shown in the X direction. An
angle of 90 ° corresponds to the main direction of the sonication (axis of the sonic cone cone) in
the case shown.
The method of the present invention prevents a strong ultrasound carrier signal from reaching
the listener's ear. For this purpose, a reflector 5 is provided on the medium cone cone 2 in the
distance from the ultrasound transmitter 1 so that the sound waves are deflected in a new
direction. FIG. 3 shows a corresponding arrangement, in which the cone of the ultrasound carrier
signal 2 and the cone of the audio signal 3 are shown.
An advantage of the method of the invention is that the audio signal 3 guided further by the
reflector 5 can be focused on the listener 4. This preferably takes place by means of the
corresponding shape of the reflector 5, which is designed as a concave surface, for example. As a
result, even if the space is narrow (vehicle), the reflected sound wave 3 can be well converged to
the limited space area (head area of individual listeners). In the ideal case, only the ears of the
respective listener are reached, and further reflections on the listener's head are avoided.
The minimum distance necessary to form the audio signal 3 to be modulated additionally by
reflection is not the direct empty space between the ultrasound transmitter 1 and the listener 4
but the corresponding of the reflector 5 Can be angled by This makes it possible, in some cases,
to use only a few possible mounting positions. In another embodiment, a plurality of reflectors 5
can be arranged sequentially, deflecting the sound waves in succession. The required path
section is thereby achieved by multiple reflections (not shown).
A further advantage is the means of separating the audio signal 3 from the ultrasound carrier
signal 2. If there is sufficient distance from the ultrasound transmitter 1 to the reflector 5 to form
an audio signal in air, the ultrasound carrier signal 2 is no longer needed. It is therefore possible
to attenuate the (strong) ultrasound carrier signal, and the ultrasound is strongly attenuated and
does not reach the listener. For this purpose, means for selectively fading out the ultrasonic
carrier signal 2 can be provided on the sound cone.
In an advantageous embodiment, the reflector 5 is correspondingly configured to have selective
reflection properties. That is to say that the ultrasound 2 is at the reflector 5 whose power is
significantly reduced by absorption due to its high frequency, whereas the low frequency audio
signal is reflected without being substantially attenuated. Such selective attenuation at the
reflector 5 can be achieved, for example, by an ultrasound absorbing coating of the reflector. For
this purpose, for example, microporous materials are suitable. In the simplest case, thin grid cloth
can be used for that. The ultrasound-absorbing layer here can have a smaller area than the entire
reflecting surface, since it only hits a part of the reflecting surface if the ultrasound is focused
correspondingly narrowly. On the other hand, the audio signal is sometimes slightly diffused.
In particular, the method of the invention is suitable for use in relatively small spaces, such as
vehicles. FIG. 4 schematically shows the mounting of a corresponding reflector system in a
vehicle. In this embodiment, the ultrasonic transmitter 1 is attached to the dashboard panel 6.
This provides a good construction solution in terms of the required mounting depth. This means
can accommodate the necessary cooling devices. The ultrasonic carrier signal 2 emitted obliquely
upward in this embodiment impinges on the reflector 5. The reflector is here provided in the
upper region of the windscreen 9, for example mounted in the transition region of the
windscreen and the roof lining 8 of the vehicle or as an integral part of the roof lining 8. The
ultrasound-absorbing coating of the reflector 5 strongly attenuates the ultrasound carrier signal
and substantially only the audible audio sound wave 3 is reflected. The surface curvature of the
reflector 5 additionally acts on the focusing of the audio signal 3. The main direction of the
reflection is adjusted so that the reflected audio signal 3 reaches the listener's 4 ear.
Corresponding adjustments (for example to make them fit to the size of the listener's head or to
fit separately when adjusting the seat level) are via the adjustment device at the reflector 5 and /
or It can be done by changing the direction of radiation at the ultrasound transmitter 1 (here the
instrument panel).
The basic inventive reflector system has the advantage that all elements of the system, having a
large weight and a corresponding volume, can be accommodated in a cabin area which can
provide a relatively large space. The reflector itself can be made of relatively thin and lightweight
materials (eg, aluminum, plastic, etc.). This is also advantageous in terms of safety. Because all
heavy elements (ultrasound transmitters) are incorporated correspondingly in the stable deep
areas of the vehicle, they are also correspondingly shielded empty in case of an accident (the risk
of damaging the head area is reduced) To do).
In another embodiment (not shown), the reflector system can be extended by the safety device as
follows. That is, the ultrasound signal is automatically blocked or attenuated when the object or
person approaches a region of high ultrasound intensity (the ultrasound cone between the
ultrasound transmitter and the reflector). Identification of penetration into the ultrasound cone
cone can usually be done by proximity sensing according to the prior art, for example by means
of an infrared detector or an ultrasound detector.
The method for directed audio illumination is based on a modulated ultrasound carrier signal and
is characterized by low space requirements, high convergence of the audio signal, and reduced
ultrasound exposure to the listener. This is especially suitable for use in small spaces, for
example vehicles, and if configured accordingly, it is possible to provide different audio signals to
the individual seats, without any acoustical superposition occurring.