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TECHNICAL FIELD The present invention relates to a speaker device. Conventionally, in order to
apply motional feedback (hereinafter referred to as MFB) to the speaker, the vibration detector 3
is attached to the speaker unit 2 as shown in FIG. To the inverting input of the power amplifier 1.
However, when the vibration detector 3 is attached to the diaphragm of the speaker unit 2, the
vibration characteristics of the speaker unit 2 change, and the weight of the vibration system is
very light, especially at high frequencies & (1000'Hz or more). A large increase in weight when
attached causes a significant decrease in efficiency, and a sharp resonance taste is generated at
the high detection limit local wave number of the detector 3 and the phase rotation is large. For
these reasons, it has been considered impossible to return the high-pitched speaker. OBJECTS OF
THE INVENTION It is an object of the present invention to provide a speaker apparatus capable
of applying an MFB to a high-tone speaker without causing the above problems. Configuration of
the Invention In the present invention, a feedback microphone (acoustoelectric converter) is
provided in the vicinity of the diaphragm of the high-tone speaker. Since the reproduction sound
of the high-tone speaker is detected in a non-contact manner, MFB can be applied to the hightone speaker without causing the above problem. DESCRIPTION OF THE PREFERRED
EMBODIMENT An embodiment of the present invention is shown in FIGS. That is, in FIG. 2, the
high sound speaker (hereinafter referred to as tweeter) 7 and the low frequency speaker
(hereinafter referred to as woofer) 9 are incorporated in the speaker cabinet 5, and the
microphone 6 is provided near the center of the tweeter equalizer grille 8. ing. The output signal
of the microphone 6 detects both the reproduced sound of the tweeter 7 and the reproduced
sound of the woofer 9, and is fed back to the inverting input of the power amplifier 1 through the
feedback circuit 4 as shown in FIG. The reference numeral 10 drives the tweeter 7 and the
woofer 9 in a network. When configured in this way, the microphone 6 detects sounds in the
entire reproduction frequency band from the bass to the treble as the speaker system, and so-
called acceleration feedback is applied to the tweeter 7 and the woofer 9, distortion of the
tweeter 7 and the woofer 9 Is reduced by the feedback amount, and in the woofer 9 in particular,
the low frequency lowest resonance frequency is lowered. This situation is shown in FIG. 4,
where the horizontal axis is the frequency, the vertical axis is the reproduction sound pressure,
the solid line a is the characteristic before feedback and the broken line is the characteristic after
feedback, and the low frequency lowest resonance frequency is lowered. it is obvious. It is
conceivable to stand a stand or an angle on the front face of 9 as a possible thing to think about
the attachment of the microphone 6, but the stand or the angle receives resonance sound from
the speaker or resonates or reflects it. Not only does the characteristic disorder occur in the
irregularities, but at high frequencies, the wavelength becomes short and the distance between
the tweeter 7 and the microphone increases, so that the Q phase can not be turned back.
Assuming that the sound velocity is 340 m7 seconds, if the tweeter 7 and the microphone 6 are
separated by 8.5 am, the phase exceeds 90 degrees in the quarter wavelength I KHz or more, and
the negative feedback becomes less than I KHz. Although it is limited, if the microphone 6 is
provided at the center of the sound with a small phase delay at the high sound on the axis of the
tweeter 7 as in this embodiment, in principle it can be returned to around the high frequency
reproduction limit frequency of the tweeter 7 Since the tweeter 7 is generally provided with the
equalizer grille 8 so that the frequency characteristic at the listening point is flat, the small
microphone 6 is provided at the center of the equalizer grille 8, including the microphone 6, it
becomes flat at the listening point In the form of an equalizer like this, alignment like the angle
on the woofer 9 can also be prevented. However, the microphone 6 does not have to be attached
to the equalizer grille 8 of the tweeter 7 and may be fixed to a stand or a hole may be provided in
the center of the diaphragm of the tweeter 7 and the microphone 6 may be fixed therein.
However, if it is set near the acoustic center of the tweeter, it is possible to apply feedback from
high to low tones. Also, even if the microphone 6 is set at a position away from the axis of the
woofer 9 as in this embodiment, the reproduction sound pressure of the woofer 9 can be
detected correctly. The difference between the on-axis and the periphery of the speaker is only
about 1 to 3 dB, and since the wavelength is long, the wave front is uniform over a wide range
and the phase rotation is very small and negligible. Also, the microphone 6 is not necessarily
directed to the woofer 9 by using a nondirectional microphone. Further, it is desirable that the
microphone 6 be closer to the sound source in terms of phase and sensitivity, and the tweeter
and the woofer should be as close as possible considering the directivity characteristics at the
listening point of the speaker system. Incidentally, although the acceleration feedback has been
described in this embodiment (5), the speed feedback and the amplitude feedback can also be
implemented as in the prior art. According to the present invention, the loudspeaker apparatus of
the present invention can apply MFB to high-pitched loudspeakers without causing the abovementioned various problems, and can also apply feedback to bass, which is extremely useful. It
has the effect of
Brief description of the drawings
1 is a block diagram of a conventional MFH, FIG. 2 is a perspective view of an embodiment of the
present invention, FIG. 3 is a block diagram of the MFB, and FIG. 4 is a sound pressure frequency
characteristic diagram before and after feedback.
DESCRIPTION OF SYMBOLS 1 ... Power amplifier, 4 ... Feedback circuit, 5 ... Cabinet, 6 ...
Microphone, 7 ... Loudspeaker, 8 ... Equalizer grille, 9 ... Bass speaker, 10・ ・ ・ Network agent
Patent attorney Atsushi Miyai (6) Fig. 2 Fig. 3 □ Heart wave number (Hz) Fig. 4
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