Electrical audio signal processing systems and devices – Noise or distortion suppression – Interpolation
Patent
1984-06-12
1986-05-27
Rubinson, Gene Z.
Electrical audio signal processing systems and devices
Noise or distortion suppression
Interpolation
381 59, 381 96, H04R 102, H04R 304, H04R 2900
Patent
active
045920885
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a speaker apparatus where the sound pressure characteristic of a speaker is controlled by MFB (Motional Feed Back) whereby the lowest resonance frequency is decreased so that the reproduction capability in the low frequency range is improved.
BACKGROUND ART
The so-called MFB technique has been known, according to which the acceleration of the diaphragm of a speaker is detected by a certain method and the detected output is negatively fed back to a power amplifier thereby to lower the lowest resonance frequency of the speaker.
In the case when a microphone is used a method for detecting the acceleration of the diaphragm of a speaker, an angle arm is provided in front of the diaphragm. The microphone is fixed in the center part of the angle arm and the sound pressure reproduced by the diaphragm is detected by the microphone. This method has the advantage of detecting vibration without any contact between the diaphragm and the microphone. However, according to the above method, the angle arm for fixing the microphone which protrudes in front of the diaphragm disturbs the radiation of sound; the angle arm resonates; the external appearance is undesirable; and furthermore, since the speaker and the microphone should be always built in as a pair, there is a problem that the freedom of design is limited.
Especially, after MFB is applied, the low frequency region is enhanced and the displacement of the diaphragm increases. In order to avoid any touch of the diaphragm with the angle arm, the angle arm should be kept at a distance from the diaphragm. However, if this is done, there arises a problem that the feedback upper-limit frequency (the maximum frequency at which the amount of feedback becomes 0 dB) becomes low since the rotation of the phase of sound waves from the diaphragm to the microphone increases. Moreover, if the microphone is provided in front of the speaker, the influence of the so-called Doppler distortion due to the Doppler is unavoidable.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a speaker apparatus wherein the detection by a microphone scarcely influences the reproduction on sound; limitation of design is small; design is excellent; and furthermore, the feedback upperlimit frequency can be increased and the influence of Doppler distortion is small.
The above and other objects are accomplished according to the invention by the provision of a speaker apparatus comprising an input terminal for receiving an input signal; a speaker for radiating a sound wave, the speaker having a sound wave radiation axis; a power amplifier connected between the input terminal and the speaker for driving the speaker to produce a sound wave; a feedback amplifier; a microphone for detecting the sound wave from the speaker and connected to the power amplifier via the feedback amplifier for feeding back to the power amplifier a feedback signal which has a frequency range below an upper limit frequency, the microphone being disposed in a plane which is substantially perpendicular to the direction of the sound wave radiation axis, and wherein said plane substantially contains an acoustic center of the speaker and the microphone is located at a distance from the sound radiation axis which is not greater than 1/4 of the wavelength corresponding to the upper limit frequency of the feedback signal.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view for explaining the principle of this invention;
FIG. 2 is a diagram of sound pressure-frequency characteristic at points A-E in FIG. 1;
FIG. 3 and FIG. 4 are diagrams of sound pressure-frequency characteristics before and after feedback at points A and C;
FIG. 5 and FIG. 6 are diagrams of sound pressure-frequency characteristics showing the amount of feedback in FIG. 3 and FIG. 4;
FIG. 7 is a block diagram for explaining the principle of measuring the sound pressure-frequency characteristics;
FIG. 8 is a perspective view of a first embodiment of this invention;
FIG. 9 is a perspective view of a sec
REFERENCES:
patent: 4100380 (1978-07-01), Gosswiller
patent: 4268719 (1981-05-01), Manger
patent: 4276443 (1981-06-01), Meyers
patent: 4395588 (1983-07-01), Franssen et al.
Byrd Danita R.
Matsushita Electric - Industrial Co., Ltd.
Rubinson Gene Z.
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