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TECHNICAL FIELD The present invention relates to a speaker device for controlling the sound
pressure characteristic of a speaker by motional feedback (hereinafter referred to as MFB) and
reducing the lowest resonance frequency (hereinafter referred to as f). I'm sorry. The
configuration of the prior art and the problems thereof As shown in FIGS. 1 and 2, the MFB of the
loudspeaker detects the vibration of the loudspeaker 13 from the loudspeaker 13 by any method
and feeds the power amplifier 12 on the input side through the feedback amplifier 14 It is known
that negative feedback is applied, and feedback of a signal proportional to the acceleration of the
speaker 13 can reduce the speaker 13 by far. When a microphone is used to detect the
reproduction sound pressure when detecting the vibration of the speaker, an angle 9 for fixing
the microphone is provided at the front center of the diaphragm 8 as shown in FIG. The
microphone 11 was fixed at the center. In FIG. 1, 1 is a yoke, 2 is a magnet, 3 is a plate, 4 is a
frame, 5 is a voice coil, 6 is a damper, 7 is a drive cone, and 10 is an edge. In this way, there is an
advantage that vibration can be detected in a non-contact manner in the vibrating portion of the
speaker 13, but there is a problem that the angle 9 for fixing the microphone disturbs the
radiation of sound and the angle 9 resonates further. In addition, the design is not excellent, and
there are many restrictions in terms of the degree of freedom of design, such as the personal
decoration phone 11 must be paired with the speaker 13 in an appropriate size. SUMMARY OF
THE INVENTION The present invention solves such problems, and microbon detection has no
influence on sound reproduction, has less design restrictions, and can be made superior in
design. A speaker device is provided. According to the present invention, when the reproduction
sound pressure of the speaker is detected by the microphone, the output of the microphone is
input to the speaker in a frequency range lower than the frequency at which the distance
between the speaker and the microbon becomes I / i wavelength. It is intended to return to the
side. In this way, the microphone can be 11 m from the speaker within the range not exceeding
the wavelength A at the feedback upper limit frequency, whereby the sound reproduction can not
be reduced, and the restriction on the dI is also small. Can be realized. Description of the
Embodiment FIG. 3 shows that the microphones are placed at points A, B, C, D and E at the X
mark in the figure at a height of 1 Crn above the baffles of the speaker box 16, and the radiation
sound pressure of the speaker 13 is calculated. 1) It shows the situation when it was decided.
Figure 4A, 13. Sound pressure frequency characteristics of points C, D and E are shown. The
vertical axis is sound pressure, and the horizontal axis is frequency. As is clear from this, it can be
seen that the distance characteristic in the directivity direction of 90 degrees from the on-axis of
the speaker 13 has no significant change in the frequency characteristic as compared with the
point A at 0 degree on the axis. This indicates that when detecting the vibration characteristic of
the speaker 13, it is not always in close contact with the speaker 13 as conventionally
considered, and it is not necessary to arrange a microphone on the axis thereof. However, in
order to apply feedback, it is necessary that the phase does not rotate by more than 9Q degrees.
Therefore, the distance between the microphone and the speaker 13 can be Nfi to a range not
exceeding% of the wavelength at the feedback upper limit frequency. By using this principle, the
setting position of the microphone can be given a great degree of freedom, and when applying
the MFB to the speaker 13, it is not necessary to provide the microphone inside the speaker box
16 or the speaker unit. Even when MFB is applied to a speaker already used by the user, it
becomes possible to install a microphone on an adapter prepared as an external adapter.
Assuming that the sound velocity is 3401 rL / sec, when applying negative feedback to the
speaker 13 up to 340 Hz, it is possible to 4E the micropon from the speaker 13 up to 25 crIL,
which is a peak wavelength. Also, considering from FIG. 4 that the frequency characteristic of 20
oHz or less is substantially equivalent to the point A up to the point D (20cIIL), the upper limit
frequency of the feedback is set to 200 to 300 Hz, and between the micropon and the speaker 13
It is desirable that the distance be within 20 to 25 cm. The broken lines in FIGS. 5 and 6 are the
characteristics after feedback at point A and point 0 in FIG. 3, respectively, in which the feedback
amount ? is adjusted so that the frequency characteristics after feedback are almost similar. is
there. In FIGS. 5 and 6, 17.19 is the diaphragm acceleration after the feedback, and 18 is the
diaphragm acceleration when the MFB is not applied. FIGS. 7 and 8 show the feedback amount in
each state of FIG. 5 and FIG. 6, where the hatched portion is negative feedback and the other is
positive feedback. The feedback upper limit frequencies are F and G, respectively. A block
diagram of this measurement is shown in FIG. The acceleration pickup 23 is fixed to the central
portion of the diaphragm of the speaker 13, and the input signal frequency applied to the
speaker 13 from the input terminal through the power amplifier 12 ░ speaker cord 24 is one to
pull the acceleration by the pickup 23 22. Detect and pick up the output of the pickup cable 22.
It is drawn on the level recorder 20 via the pickup amplifier 21. When the switch S1 is closed,
the microphones 11. Switch S +, di feedback amplifier 14. The feedback is applied via the volume
R1, and at this time, the feedback changes ? by the volume R1. Therefore, the microphone 11
and the switch SX in FIG. If the feedback circuit consisting of the volume R1 and the like is
integrated as the adapter 25, the MFB can be easily applied to the existing speaker. FIG. 1o
shows a specific embodiment of the present invention, in which an adapter 25 is placed in the
vicinity of the speaker box 15, and on this adapter 25, the microphone 11 and switch S + shown
in FIG. . It incorporates a feedback circuit consisting of a volume R1 and the like. In this way, an
MFB speaker can be easily configured. Although it is desirable that the adapter 25 be as close as
possible to the speaker box 15, the adapter 25 does not have to be in close contact with the
speaker box 15, and the degree of freedom of installation is extremely thick. If the adapter 25 is
kept far away from the speaker 13 and the feedback amount is fixed to a certain value or less
even if the phase is shifted at a high frequency, the sound receiving pressure of the microphone
11 is only as far away from the speaker 13 Since it decreases and the amount of feedback
automatically decreases, problems such as oscillation do not occur. That is, the return amount
may be equal to or less than Q dB at a frequency at which the phase difference between the
reproduction sound of the speaker 13 and the detection signal of the microphone 11 is 90
degrees or more. In the embodiment, although the output signal of the microphone is fed back as
it is, it is of course possible to make fo and its sharpness QO variable even if fed back through the
integration circuit, or by applying speed feedback and amplitude feedback. It is. Effects of the
Invention As described above, according to the present invention, it is not necessary to
incorporate a microphone, which is a detection element of MFB, into a speaker unit or a speaker
box, for example, by attaching it as an adapter to a speaker already used by a user. As a result, it
is possible to obtain an excellent effect that it is not necessary to use a special speaker dedicated
to MFB as in the prior art.
Brief description of the drawings
1 and 2 are ifr views and a block diagram of a conventional speaker device, FIG. 3 is a
perspective view of the present invention, and FIGS. 4 to 8 are characteristic diagrams thereof,
and FIG. FIG. 1 is a block diagram showing the state of measurement in FIGS. 5 to 8 and FIG. 1 o
is a perspective view of an embodiment of the present invention.
1 и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и damper ииииииии
Drive cone, 8 иии Diaphragm, 9 иии Angle for fixing microphone, 10 иии Edge, 11 иии Microphone и 12 иии
Power Amplifiers 13 иииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииии Speaker When not applying the
diaphragm acceleration, 20 ..... Level recorder, 21 ..... Pickup antenna, 22 ..... Pickup cable, 23 .....
Pickup, 24 .....? ? ? Speaker cord, 25 ? ? ? adapter, S + .... switch diaphragm acceleration
characteristics during open 26 ... switch S1, diaphragm acceleration characteristics of 27, 28 ......
switch S1 closed. Name of Agent Attorney Nakao Toshio Other 1 person Figure 1 Figure 2 Figure
43! 5 Fig. 71 71
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