Electrical audio signal processing systems and devices – Acoustical noise or sound cancellation – Counterwave generation control path
Reexamination Certificate
1998-01-09
2001-03-06
Chang, Vivian (Department: 2747)
Electrical audio signal processing systems and devices
Acoustical noise or sound cancellation
Counterwave generation control path
C381S071100, C381S094100
Reexamination Certificate
active
06198829
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to processes and devices for focusing acoustic waves.
According to a first aspect, the invention relates more particularly to a process for sound-sweeping a space which disturbs the propagation of acoustic waves so as to transmit in this space information in the form of acoustic waves by means of a number n of loudspeakers, n being a natural integer at least equal to 1, this process including sound-sweeping steps in the course of which at least one acoustic signal S(t) carrying information is transmitted in at least one zone, termed a “target zone,” which belongs to the space to be sound-swept, this transmission being carried out by having acoustic signals s
i
(t) emitted by at least one subset of so-called “active” loudspeakers, which subset includes at least one loudspeaker chosen from among the n above-mentioned loudspeakers.
BACKGROUND OF THE INVENTION
Numerous examples of spaces which disturb the propagation of acoustic waves are known. Among other examples there may be mentioned:
railway stations and air terminals, or more generally public places in which multiple reflections of sound waves make it difficult to understand the broadcast sound messages intended for users,
and the spaces in which multi-scattering media would be arranged at least locally, that is to say media in which are dispersed or distributed elements which reflect or individually scatter the acoustic waves, with weak absorption, of a nature such as to cause a spreading of at least one order of magnitude of the duration of an acoustic pulse.
The objective of the present invention is in particular to optimize the transmission of information inside such a space.
SUMMARY OF THE INVENTION
To this end, according to the invention, a process of the kind in question is essentially characterized in that in the course of each sound-sweeping step, each active loudspeaker i emits a signal
s
i
(
t
)
=
∑
j
a
j
·
h
ij
(
-
t
)
⊗
S
(
t
)
,
(
1
)
where:
h
ij
(−t) represents the temporal inversion of the impulse response h
ij
(t), previously determined and stored, between loudspeaker i and a predetermined so-called “calibration” point j belonging to the target zone, the target zone comprising a number p of calibration points, p being a natural integer at least equal to 1, the impulse response h
ij
(t) corresponding to the acoustic signal received at the point j when loudspeaker i emits a short acoustic pulse,
and the coefficients a
j
are predetermined weighting coefficients.
By virtue of these arrangements, which allow acoustic focusing toward the target zone, the information transmitted in the form of acoustic waves is received perfectly clearly in the target zone, and much less clearly outside the target zone, this presenting no drawback and possibly even constituting an important advantage insofar as the target zone is chosen suitably.
In preferred embodiments of the first aspect of the invention, one and/or other of the following arrangements may possibly also be resorted to:
the weighting coefficients a
j
are all equal to 1;
the subset of active loudspeakers comprises all the loudspeakers of the space to be sound-swept;
the number p of calibration points of the target zone is at least equal to 2;
the number n of loudspeakers is at least equal to 2;
the signal S(t) corresponds at least in part to a sound signal chosen from among the signals representative of the human voice and the signals representative of musical snatches;
the space to be sound-swept is a place which receives the public, and the signals S(t) correspond at least in part to public information messages;
in the course of at least certain of the soundsweeping steps, a number q of target zones is simultaneously sound-swept, where q is a natural integer at least equal to 2, each active loudspeaker i then emitting the superposition of q acoustic signals
s
i
,
k
(
t
)
=
∑
j
a
j
·
h
ij
(
-
t
)
⊗
S
k
(
t
)
,
(
2
)
where k is a natural integer lying between 1 and q corresponding to each target zone, S
k
(t) representing the information-carrying acoustic signal intended to be broadcast in the target zone of index k: use is thus made of the above-mentioned property of the process according to the invention, according to which each signal S
k
(t) is perfectly received in the target zone k, but very poorly received, or not received at all, in the other target zones;
the target zone considered in at least certain of the sound-sweeping steps is as restricted a zone as possible comprising at least one calibration point and in which there is at least one person who is the destination of a voice message represented by the signal S(t).
Moreover, the first aspect of the invention also has as subject a device for implementing a process as defined above, for sound-sweeping a space which disturbs the propagation of acoustic waves, this device including:
a number n of loudspeakers distributed inside the said space, n being a natural integer at least equal to 1,
at least one input pathway for receiving a signal S(t) carrying information to be transmitted in the form of acoustic waves in at least one zone, termed the target zone, which belongs to the space to be sound-swept, this transmission being carried out by having acoustic signals s
i
(t) emitted by at least one subset of so-called active loudspeakers, which subset includes at least one loudspeaker chosen from among the n above-mentioned loudspeakers,
a signal processing system for determining each signal s
i
h
(t) via the formula:
s
i
(
t
)
=
∑
j
a
j
·
h
ij
(
-
t
)
⊗
S
(
t
)
,
(
3
)
where
h
ij
(−t) represents the temporal inversion of the impulse response h
ij
(t), previously determined and stored, between an active loudspeaker i and a predetermined so-called “calibration” point j belonging to the target zone, the target zone comprising a number p of calibration points, p being a natural integer at least equal to 1, and the impulse response h
ij
(t) corresponding to the acoustic signal received at the point j when loudspeaker i emits a short acoustic pulse,
and the coefficients a
j
are predetermined weighting coefficients,
the signal processing system being linked to the input pathway so as to receive the signal S(t) and to the various loudspeakers so as to transmit respectively thereto the signals s
i
(t).
Advantageously, this device furthermore includes means for selecting the target zone within the space to be sound-swept.
According to a second aspect, the subject of the present invention is a process and a device for focusing and temporal compression of acoustic energy. The term “acoustic” should be taken in a general sense, without limiting it to the audible frequencies. It may even be applied to radio waves, insofar as they have a mode of propagation which is akin to that of acoustic waves.
The invention is applicable in numerous fields of the art, among which may be mentioned the following.
The invention makes it possible to concentrate acoustic energy into a given location. This location may for example be that of a fixed target which it is sought to locate or destroy. The latter case is that of lithotrity or the destruction of a tumor in the body. It is also that of the destruction of an explosive contraption, such as a mine.
The location (or a set of such locations) can even be situated on a manufacturing line where objects each of which is to receive one or more intense, brief and localized pulses of acoustic energy are presented in succession.
It also allows communication between a station and a receiver placed at the location at which the energy is concentrated, with discretion ensured by the selective character of the energy concentration; several receivers may be provided, at the cost of an energy distribution.
Processes are already known for examining a medium so as to pinpoint therein reflecting targets and/or for destroying the targets, using the temporal reversal of the signals received by th
Fink Mathias
Lewiner Jacques
Chang Vivian
Christensen O'Connor Johnson & Kindness PLLC
Mei Xu
Societe pour les Applications du Retournement Temporel
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