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JPS59207799

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DESCRIPTION JPS59207799
[0001]
The present invention relates to an electroacoustic transducer that converts encoded digital
electrical signals directly into analog acoustic signals. In recent telecommunication, PCM signals
are also used in the audio frequency range, but this is because there is noise protection
compared to conventional amplitude modulation and analog signals <<, so the dynamic range is
In addition to the basic merits of large, low distortion transmission, other aspects of signal
processing, such as recording in a large capacity memory, combining signals with video and
other data, and using a processor to analyze the signal, etc. It is because it has immeasurable
merits. Conventionally, in order to finally convert the encoded digital electrical signal having
such features into an acoustic signal, it is converted into an analog electrical signal by an
electrical A converter and this is converted into an acoustic signal by a normal electrical acoustic
transducer. The method of conversion was common. However, this method is not only expensive
and requires an A converter, but also requires an output amplifier that can withstand the
maximum value of the converted analog electrical signal, so that the normal output is small and
uneconomical compared to the capacity of the amplifier. There is a drawback that the inherent
merits of digital signal processing are reduced, such as increased nonlinear distortion and limited
dynamic range. There are electro-acoustic transducers which convert digital electrical signals
directly into analog acoustic signals in order to eliminate these drawbacks. For example,
Japanese Patent Publication No. 54-12049 discloses a transducer having a structure in which
one piezoelectric element is provided with an electrode for the number of bits, and this
piezoelectric element is coupled to one diaphragm. However, in practice, accurate signal
reproduction is difficult due to the divided vibration of the piezoelectric element. Another
example is an electrodynamic transducer, in which a number of voice coils equal to the number
of bits are wound on a common winding frame, and a speaker having a structure in which this
winding frame is coupled to one diaphragm is present. In the speaker of this structure, the voice
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coil of the bit without the input signal pulse also moves, so the back electromotive force lowers
the efficiency, and in the case of many bits, the number of coils and the coil weight increase and
the vibration system becomes excessive. It is difficult to realize as a speaker. The present
invention relates to an electroacoustic transducer capable of directly converting a digital
electrical signal into an analog acoustic signal without losing the merits of the digital signal
processing and eliminating all the above-mentioned drawbacks. The operation principle and
structure will be described in detail with reference to FIGS. 1 (aL (1)), (c), (d) and FIGS. 2 and 3.
FIG. 1 (a L (b), (c), (d) is an example showing the correspondence between the encoding of the
signal applied to the electroacoustic transducer of the present invention and the waveform.
FIG. 1 (a) shows the correspondence between the analog number and the digital number, N is the
number of bits, and the most significant bit (MSB) is a bit for discriminating the polarity of the
analog signal. The analog value is converted to a binary code consisting of the remaining N-1
bits. Although each bit, for example the N-1 bit, corresponds to 2N4 in the original analog value,
this corresponding analog value is called the bit weight. (MSB) is l if the corresponding analog
signal is positive and 0 if it is negative. FIG. 1 (b) is a digital electrical signal in which the signal
represented by the binary code in FIG. 1 (a) is a digital electrical signal, and the code 1
corresponds to one electrical pulse. In the figure, lb, lb '... Indicate the first bit of electric pulse,
2b. 2b '... Is the second bit electrical pulse ヲ, (N-1) b, (N-1) b'.. Is the N-1 bit electrical pulse, and
Mb and Mb 'are the MSB electrical pulse Each represents. The dotted line A is an analog signal,
and ASb, ASb ', ... are the sampled analog signals. FIG. 1 (c) is a digital electrical signal waveform
applied to an electroacoustic transducer using the driving method of the present invention. These
signals are digital electrical signals constituted by constant amplitude pulses whose polarity is
defined by the MSB signal. FIG. 1 (d) shows the sound pressure radiated from the sound
generation part of each bit of the electro-acoustic transducer of the present invention and the allbit synthetic sound pressure waveform. Since the applied signal pulse has a constant amplitude,
the sounding part of the transducer coupled to each bit needs to be structured or driven to be
able to emit sound pressure proportional to the weight of each bit is there. That is, ld, ld '... Is the
sound pressure radiated from the sound producing portion corresponding to the first bit, and
assuming that the sound pressure thereof is 1, the sound pressure 2d corresponding to the
second bit 2d'. .. Are required to have a magnitude 2N-2 and so on. The sound pressure CN-1) d,
(N-1) d '. The sound pressure from each of these sound producing parts is spatially synthesized to
become ASd, ASd ', and when averaged, it becomes an acoustic signal Ad (dotted line) equal to
the original analog waveform. The structure and operation of the electrodynamic electroacoustic
transducer of the present invention will be described with reference to FIG. (Hereafter, all the
same parts are indicated by the same number. 2.) In FIG. 2, each section 21, 22. 28 2 (N-1)
surrounded by a one-dot chain line is an electrodynamic conversion element constituting the
electrodynamic electroacoustic transducer of the present invention, Is equivalent to the first bit,
22 is equivalent to the second bit,..., And the following 2 (N-1) are electrokinetic conversion
elements equivalent to the (N-1) bit.
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(N-1) electrokinetic conversion elements 21, 22. ... 2 (N-1) are respectively the diaphragm 81, 82
° ... 3 (N-1), and the voice coils 41, 42 fixed to the respective diaphragms respectively. ... 4 (N-1)
and magnetic circuits 51, 52. -It consists of 5 (N-1), and it arrange ¦ positions concentrically
sequentially around the 1st bit equivalent electrodynamic conversion element 21 centering
around it. The above magnetic circuits 51, 52. ... 5CN-1) may be installed separately for each
electrodynamic conversion element, but as shown in FIG. 2, a ring-shaped magnet and magnetic
poles are alternately combined to form an integral frame 6 on the outermost periphery It may be
a mounted structure. Each diaphragm of each of the electrodynamic conversion elements
arranged concentrically has an edge on the inner and outer periphery (only the outer periphery
of the electrodynamic conversion element equivalent to the first bit corresponds to the outer
periphery), and a concentric support 71. 72 and the outermost periphery are supported at a
predetermined position by the frame 6. Furthermore, the electrodynamic conversion elements
(21, 22,... 2 (N-1)) have an electroacoustic conversion efficiency proportional to the weight of the
corresponding bit. In general, the electroacoustic conversion efficiency of the electrodynamic
electroacoustic transducer is expressed by the following equation. However, η · · ·
electroacoustic conversion efficiency B air gap magnetic flux density L voice coil length RE · voice
coil wire DC resistance SD · diaphragm area Ml · diaphragm mass M2 voice coil mass or Zs is the
characteristic impedance density, 凧 is additional mass is there. In order to make each of the
electroacoustic conversion efficiencies of the (N-1) electrodynamic conversion elements have a
size proportional to the weight of the corresponding bit, η represented by the above equation
(1) has a predetermined size As described above, the respective values of B, L, RE, SD, Ml, and M2
are set independently or at the same time in association with each other. For example, in order to
set each mass to a specified value regardless of the area of the diaphragm, the thickness of each
diaphragm is adjusted, or diaphragm materials of different materials or degrees of foaming are
used. With regard to the voice coil, in order to obtain predetermined impedance, mass and voice
coil wire length, it is also conceivable to use a combination of conductive materials having
different specific resistance values simultaneously with the cross-sectional area of the coil wire.
FIG. 3 is a schematic diagram showing the interconnection of N-bit digital electrical signal
sources with the electroacoustic transducer of the present invention. The component parts of
each electrokinetic conversion element corresponding to each bit are the same as in FIG.
Sl、S2. .. 5 (N-1) is a switch circuit operated by the MSB polarity discrimination signal to
switch the polarity of the signal, and 7 is a polarity discrimination circuit. FIG. 4 shows another
configuration of the electrodynamic electroacoustic transducer according to the present
invention, wherein each of the (N-1) voice coils 41, 42. -1 (N-1) with series variable resistors R1,
R2 and -R (N-1) connected respectively, and overall efficiency including the efficiency drop of
each electrokinetic conversion element due to the voltage drop of the series variable resistor Is
made proportional to the weight of each bit. When the N-bit digital signal shown in FIG. 1 (C) is
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applied to the electroacoustic transducer of the present invention, the signal pulse has a constant
amplitude (constant voltage) and corresponds to each bit of the transducer. Each of the
electrodynamic conversion elements has an electroacoustic conversion efficiency proportional to
the bit weight, and as a result, it emits sound pressure proportional to each bit weight, and these
are combined in space to obtain FIG. 1 (d). It emits the indicated analog sound signal. As
described above, the present invention is an electrodynamic electroacoustic system in which the
diaphragms of (N-1) electrokinetic transducer elements whose electroacoustic conversion
efficiency is equal to the weight of each bit are arranged concentrically with each other. A
transducer, in which each electrokinetic transducer is completely independent, there is no
adverse effect due to electrical mutual interference, and since the acoustic arrangement of the
electrokinetic transducer and the coupling are close, analog waveform It has the feature that
reproduction is faithful. The electrodynamic electroacoustic transducer according to the present
invention can be directly converted into an analog acoustic signal by applying an N-bit encoded
digital electrical signal to each voice coil, such as a telephone and voice synthesis By adding an
acoustic circuit such as an ear bat, or a diffuser, a horn, etc., as a vocal part of the device, it has
wide practicality in the field of audio and the like.
[0002]
Brief description of the drawings
[0003]
Figures 1 (a), (b), and (cL (d) are the correspondence diagrams between the analog value and the
N-bit binary code, respectively, and the waveform of the binary code digitally encoded with the
binary code and the sampled analog signal FIG. 6 is a waveform correspondence diagram, an
N−1 bit digital electrical signal waveform diagram applied to a converter, and an output sound
pressure waveform diagram of the converter.
Fig. 2 (aL (b) is a front view and a sectional view of the electro-acoustic transducer of the present
invention, Fig. 3 is a connection diagram of the electro-acoustic transducer of the present
invention and a digital electrical signal source, and Fig. 4 is a diagram of the present invention. It
is the same wiring diagram of another Example. 1 is an electrodynamic electroacoustic
transducer 21.22. · · · Each electro-acoustic transducer, 81, 82. .. Are the respective diaphragms
of the respective electroacoustic transducers, 41 ° 42, are also voice coils, 51, 52. · Are also
magnetic circuits, 71, 72. · · Is also a support, 6 is a frame. Special issue Island person Onokiyo141 complete company agent Patent attorney Sa Shield 彌 部 才 part 11 刀 (ら) + 1 +] (11) (11)
(c) of 11 (c)
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