Patent Application
20190141453
The present invention relates to a speaker apparatus configured to reproduce sound from an electrical signal, and more particularly to a voice coil speaker apparatus capable of reproducing sound with high fidelity over a wide frequency band.
The audible frequencies of sound that people can hear with their ears are known to range from about 20 Hz to about 20 kHz. A high fidelity (Hi-Fi) audio system is a system that provides a uniform frequency response with no distortion of the original sound in the entire audio frequency band in reproducing sound corresponding to an audio signal recorded in the form of an electrical signal. However, a typical voice coil type speaker unit uses a mechanical suspension, and thus may produce distorted sound depending on properties of the suspension, leading to low clarity of the reproduced sound and a bad frequency response.
A multi-way speaker system, which is most popular, employs a plurality of speaker units having different features in terms of frequency band in order to achieve a uniform frequency response required in the Hi-Fi audio system. The multi-way speaker system separates an audio signal in frequency bands such as high sound, mid sound, and low sound through a crossover network and reproduces the separated audio signals through speaker units specialized for the respective frequency bands to improve characteristics in terms of frequency response. However, even this speaker system may hardly avoid deterioration of reproduced sound due to the limited properties of each speaker unit, the difference in property between the speaker units and influence according to use of the crossover network and may result in lack of clarity and dynamic range of sound.
As methods to address the intrinsic issues about the speaker units, various techniques have been proposed as follows. To address an issue about the mechanical suspension of the speaker unit, there have been proposed a technique of making the suspension moved only by an electrical signal using a dual or multiple voice coils and a technique of sensing the displacement of a speaker vibration part and feeding back the same to the speaker driving device to form a control loop, thereby making the speaker vibration part move accurately.
In U.S. Pat. No. 3,686,446 titled “PUSH-PULL MOVING COIL HAVING ELECTROMAGNETIC CENTERING MEANS” issued in August 1972, Joseph W. Manger proposed a differential speaker structure with two voice coils. In U.S. Pat. No. 4,360,707 titled “DIGITALLY DRIVEN COMBINATION COILS FOR ELECTRODYNAMIC ACOUSTIC TRANSDUCERS” issued in November 1982, Joel R. Joseph and William F. Bleeke proposed a method of driving a differential speaker apparatus with two voice coils using a digital driving technique of Pulse Width Modulation (PWM).
The differential speaker addresses the issue of a resonance frequency, which is raised in the conventional speaker unit, as a speaker vibration part including voice coils and a diaphragm is moved by electromagnetic force generated by two voice coils alone without depending on mechanical spring force. However, this speaker has a drawback in that a DC current flows through the two voice coils to maintain the balance of force in addition to an AC current corresponding to the audio signal, and there is no practical structure enabling the speaker vibration part to vibrate without being displaced from the center axis of the speaker.
The motion feedback control technology is a method to improve the bass reproduction effect and reduce distortion of reproduced sound by attaching a sensor operable to sense motion of the vibration part of a speaker apparatus and controlling a driving signal by feeding back the motion signal sensed by the sensor to the speaker driving circuit.
However, reproducing bass with a sufficient volume requires the diameter of the speaker unit to be large, and it is well-known that such a large-diameter speaker apparatus has a limit as it deteriorates characteristics of high-frequency sound. Therefore, a Hi-Fi speaker system commonly employs a separate speaker apparatus dedicated to high-frequency sound and mid-frequency sound even if a woofer adopting the motion feedback technology is used.
Therefore, the present invention has been made in view of the above problems, and it is one object of the present invention to provide a high-performance, high-quality speaker apparatus capable of reproducing sound close to original sound in the entire audible frequency band, more specifically, a differential speaker apparatus having a motion feedback function with an improved sound reproduction capability in terms of, for example, reproduced frequency band, and accuracy and clarity of reproduced sound. To this end, the present invention excludes the mechanical suspension structure provided to a conventional speaker apparatus, and provides a speaker apparatus having a structure capable of making the maximum vibration displacement of the speaker vibration part larger than that of a conventional speaker apparatus such that bass of a high output power can be reproduced even by a small-diameter speaker apparatus, a structure capable of smoothly reproducing high frequency sound even with a large-diameter speaker apparatus, and a displacement sensor capable of accurately sensing the vibration displacement of a speaker diaphragm.
In order to achieve the above-mentioned object, a magnetic circuit having two magnetic air gaps is constituted by a permanent magnet, two plates, and a pole piece. When two voice coils wound around one bobbin are positioned in each of the two magnetic air gaps created by the magnetic circuit and different currents are applied to the voice coils, the directions of the generated forces are determined by the direction of the currents and the direction of the magnetic field. Therefore, the movement direction and strength of the bobbin are determined by the difference between or sum of the two forces. When the directions of the forces generated in the two voice coils are opposite to each other and the magnitudes of the forces are the same, the bobbin stops in that position.
In driving the two voice coils, the outputs of two amplifiers should be connected to the two voice coils each such that the forces act in opposite directions to maintain balance between the forces. In one voice coil of the two voice coils, an audio signal to be reproduced is directly driven through one amplifier. In the other voice coil, the audio signal is compared with the output of a displacement sensor detecting actual movement of the bobbin and the difference between the two signals is fed back to adjust the output of the other amplifier. Thereby, movement of the bobbin accurately matching the audio signal may be generated.
A speaker system of a differential driving type using such a dual voice coil cannot employ a mechanical suspension, namely a damper and an edge structure used in a conventional voice coil-type speaker apparatus to make a vibration part of the speaker move accurately along a center axis of the speaker. In order to address this issue, the present invention is configured by forming a frame structure of a rectangular instead of a circular shape, and by attaching the vibration part to the four faces of the rectangular frame of the speaker using frictionless and elastic minimized hinge structure as shown in
In addition, in the proposed speaker structure, to address the interference caused by the sound waves generated from the rear surface of the diaphragm to the sound waves from the front surface, a wing having a cylindrical structure is provided to the outer periphery of the diaphragm to minimize interference. The wing of the diaphragm is connected to the bobbin with the vibration part support such that the movement of the bobbin is transmitted to the center of the diaphragm and the wing simultaneously. This structure of the diaphragm serves to prevent standing waves, which occur in a conventional large-diameter speaker in reproducing high-frequency sound. Therefore, it is possible to manufacture a high-quality full-range speaker capable of reproducing a full range of sound from a low frequency to a high frequency with one large-diameter speaker.
As a sensor operable to sense the movement of the vibration part, any sensor capable of obtaining a displacement output at the final stage, such as an optical sensor, an acceleration sensor, a linear variable differential transformer (LVDT), an encoder, and a speed sensor, may be employed
The conventional voice coil-type speaker apparatus hardly avoids deterioration of sound quality due to the structural issues related to resonance frequency, reproduced frequency bandwidth, and sound pressure level according to frequency, and the like. To address these issues, a differential speaker apparatus has been proposed, which may be expected to reproduce sound close to the original sound and improve sound clarity and accuracy by extending the reproducible frequency bandwidth and improving the frequency response flatness. However, it has not entered the actual manufacturing stage yet. In contrast, the present invention proposes a method of practically manufacturing such a differential speaker apparatus, thereby enabling setup of a Hi-Fi audio system at a relatively low cost and application of a high-quality audio system to a portable device.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to any of the following embodiments. Various modifications can be made to the embodiments of the present invention on the basis of ordinary technology to which the invention pertains.
The bobbin 105 is supported on a frame 110 by a damper 104, a diaphragm 101 and an edge 102, and is moved accurately in the air gap along a speaker center axis. The damper 104 and the edge 102 have elasticity that constantly pulls the bobbin 105 and the voice coil 109 to the center position. The voice coil is positioned at a position where the force generated by the current flowing through the voice coil and the elastic force of the damper 104 and the edge 102 are balanced.
The configuration and the form of the magnetic circuit are not limited to this example. The magnetic circuit may take various forms such as an inner-type and an outer-type. Further, the attachment position and shape of the hinges are not limited to this example.
The two photodiodes 503a and 503b are attached to a sensor frame 505 having a partition wall so as not to be interfered with the mutual light, and the light blocking plate 502 vibrates at an intermediate position between the two photodiodes 503a and 503b. Accordingly, the amounts of light reaching the two photodiodes 503a and 503b are inversely proportional to each other, and the same amount of light is received at exactly the middle position. That is, the absolute position of the diaphragm 301 can be determined by the difference in output between the two photodiodes 503a and 503b. The output of a photodiode is a current proportional to the amount of light, and a voltage according to the displacement may be extracted through a current/voltage converter circuit.
The displacement sensor module to sense the displacement of the diaphragm can be replaced with various types of sensors such as an acceleration sensor, a linear variable differential transformer, and an encoder in addition to the optical displacement sensor in this embodiment.
The shape of the diaphragm is not limited to this example, but the diaphragm may have various shapes such as an elliptical shape and a polygonal shape. When a sound absorbing material is attached to the rear surface of the diaphragm, the intensity of sound waves emitted from the rear surface may be lowered, and thus interference at low frequency may be further reduced.
The two output currents of the optical displacement sensor 606 are converted into voltages by the current/voltage converters 607a and 607b, respectively, and supplied to the input of a first summation circuit 609 to obtain the value of difference between the two signals. Here, the output of one current/voltage converter 607a is connected to a negative input terminal of the first summation circuit 609 and the output of the other current/voltage converter 607b is connected to a positive input terminal of the first summation circuit 609. Therefore, the value of difference between the two signals becomes the output of the first summation circuit 609.
The output signal of the first summation circuit 609 is amplified and band-filtered by a gain adjustment and filter stage 608, that is, unnecessary noise is removed, and only a necessary audible frequency band is extracted and then connected to a positive input of a second summation circuit 610. Further, the output of the preamplifier 602 is supplied as a negative input of the second summation circuit 610, and thus the difference between the two inputs becomes the output of the second summation circuit 610. The output of the second summation circuit 610 is amplified by the second power amplifier 603b and then supplied to the second voice coil 605b of the speaker apparatus 604. Here, the output of the second power amplifier 603b is connected such that the direction of the force generated by the second voice coil 605b is opposite to the direction of the force generated by the first voice coil 605a. That is, when the outputs of the two power amplifiers 603a and 603b have the same phase, the directions of forces generated by the two voice coils 605a and 605b are opposite to each other.
More details of the principle of the motion feedback control operation of the speaker driving device are given below. The audio signal 601 drives the first voice coil 605a by the preamplifier 602 and the first power amplifier 603a, and the voice coil causes the speaker diaphragm 301 to move. Here, when the movement of the diaphragm 301 is larger than the audio signal, the difference between the two output currents of the optical displacement sensor 606 becomes larger. Then, the difference between output voltages of the current/voltage converters 607a and 607b and the output voltage of the first summation circuit 609 increases. As a result, the output of the gain adjustment and filter stage 608 and the output of the second summation circuit 610 also increase, which increases the output of the second power amplifier 603b, leading to an increase in the current supplied to the second voice coil 605b and the generated force. Thus, the motion of the diaphragm 301 is reduced. When the motion of the diaphragm 301 becomes smaller than the audio signal, an operation opposite to that of the above example is performed, and eventually a motion of the diaphragm consistent with the audio signal is generated.
The present invention provides a high-performance, high-quality speaker apparatus capable of reproducing sound close to original sound in the entire audible frequency band, more specifically, a differential speaker apparatus having a motion feedback function with an improved sound reproduction capability in terms of, for example, reproduced frequency band, and accuracy and clarity of reproduced sound. Therefore, the present invention may have a useful application in this field.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2016-0066384 | May 2016 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2017/005490 | 5/26/2017 | WO | 00 |
