JP2004328692A - Cordless speaker system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems such that a signal transmission cable, a power supply cable and the like are inconvenient to carry, complicated in installation and become obstructive although such cables become problematic when installing a power amplifier and a speaker with a considerable distance between in an audio reproducing apparatus. <P>SOLUTION: A power source circuit constituted by parallel-disposing a power amplifier driving battery and an electric double layer capacitor is provided in the speaker system to deal with an overcurrent caused by a rapid change of an audio signal, and a sound volume and sound quality are maintained by a small battery on the market to operate for a long period of time. Further, the audio signal is transmitted by radio, so that the speaker system is made completely cordless. Besides, as measures to further prolong the service life of the battery, a speaker switch unit using load impedance and a digital amplifier are used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a battery operated cordless speaker system with low power consumption.
[0002]
[Prior art]
Common audio playback devices are sound source playback devices such as CD, MD, and SACD players. It consists of a digital or analog power amplifier for power amplification, a speaker system consisting of a speaker unit and a speaker box, and a speaker cable.
For example, an analog or digital signal from a CD player is power-amplified by a digital power amplifier.
[0003]
Recently, digital amplifiers have been used in many consumer devices for the purpose of improving power efficiency. As shown in FIG. 3, the digital amplifier has three main functions. The digital amplifier 101 is a PWM modulator that converts an input audio signal into a pulse signal that changes in the time axis direction. The output of 101 turns on and off the switching element 102 of the power stage, and the output is reproduced as an analog audio signal through the low-pass filter 103 to drive the speaker 14. This is a general configuration of a digital amplifier. The PWM modulator 101 has a different configuration depending on whether an audio input signal is an analog signal or a multi-bit digital signal (SPDIF). In the case of analog signal input, a general PWM modulator compares an input analog signal waveform and a triangular wave with a comparator and converts the waveform into a signal having a pulse width proportional to the magnitude of the input signal. When the input signal is a digital signal, the signal is converted into a pulse signal having a duty ratio corresponding to the bit number n of the digital signal.
[0004]
When the input of the digital amplifier is a 1-bit DSD signal from a SACD player, the 1-bit signal is directly input, and the switching element of the power stage is turned on / off by the signal, and the audio signal is turned on by a low-pass filter. To play.
The audio signal power-amplified by the power amplifier is transmitted by a speaker cable to a speaker system in which a speaker unit is built in a speaker box, and is emitted to the outside as sound waves. In some audio devices, a speaker system having a built-in power amplifier, that is, a so-called powered speaker system may be employed. The transmission distance of the speaker cable varies depending on the audio device, and a long speaker cable is required for a speaker system installed at the rear of a home theater, a speaker system for playing a musical instrument, and a loudspeaker installed indoors and outdoors.
[0005]
As a power amplifier of a recent audio reproducing device, a power amplifier using a semiconductor element is often used. This is because a large output amplifier by current output can be easily configured due to the characteristics of the semiconductor itself. Large-output amplifiers can be obtained easily and at low cost, and the power of the output amplifier has been greatly increased, so the output sound pressure sensitivity is low, but it is flat over the entire frequency band of the audio signal. It is possible to use a small speaker unit and a small-capacity speaker box that can easily obtain various characteristics. Audio devices using semiconductor power amplifiers and small speakers are effective in miniaturization and space saving, but require high power output and are inefficient.
[0006]
[Problems to be solved by the invention]
By the way, in the above-mentioned conventional audio reproducing apparatus, there are many systems in which a power amplifier and a speaker are separately set at a considerable distance. In addition, microphones, music loudspeakers, and speaker systems are also separated in indoor and outdoor loudspeakers. At this time, there is an audio signal transmission cable connecting the power amplifier and the speaker system. This transmission cable is inconvenient to carry, is cumbersome to install, and is an obstacle. In the case of a powered speaker, a power cable for a power amplifier must be connected to supply power to the speaker system, and the installation is inconveniently limited to a place where power can be supplied.
[0007]
An audio device using a semiconductor power amplifier and a small speaker is effective in miniaturization and space saving, but on the other hand, the power consumed is several tens of watts to hundreds of watts, and the power efficiency is very low. To alleviate this, even the above-mentioned digital amplifier tends to be used. The power efficiency of the digital amplifier certainly exceeds 90%, which is much higher than that of the conventional analog amplifier of about 50%. However, the efficiency with which an electric signal is actually converted into sound pressure by a speaker is very low, at 10% or less, and has not yet reached a fundamental solution.
In other words, the conventional separate audio reproducing apparatus has problems of troublesome installation of the speaker system and inefficient power consumption.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problem, the present invention employs a method of incorporating a power amplifier driving battery inside a speaker system to achieve a complete cordless operation. Further, a load impedance switching circuit for reducing power consumption is used between the power amplifier side and the speaker unit side.
When a battery is driven, there is a problem in how to maintain the volume and sound quality from the speaker to reduce power consumption and extend the life of the battery, and how to respond to instantaneous power when the battery is small.
[0009]
In order to solve this problem, in the present invention, an efficient secondary battery such as a nickel hydrogen ion battery, a lithium ion battery, a CADNICA battery, a lead battery, or a fuel cell is used. However, there is no problem if a primary battery or a so-called solar battery that converts solar energy into electricity and a secondary battery are used in place of the secondary battery.
At this time, if a battery corresponding to the overcurrent is used, a battery having a very large capacity is required. In order to avoid this, an ultra-large capacity electric double layer capacitor is inserted in parallel with the secondary battery. When a large instantaneous current is required by this capacitor, it can sufficiently cope with this.
[0010]
An electric double-layer capacitor, unlike a capacitor using a dielectric, forms a capacitor by distributing positive and negative charges over a very short distance at an interface where two different layers of solid and liquid are in contact. Since the capacitance of a capacitor is proportional to the area between the opposed plates and inversely proportional to the distance, an electric double layer capacitor maximizes the area of the plates and reduces the effective distance between the plates to the molecular level. Large capacity can be realized. The capacitance of an electric double layer capacitor is three orders of magnitude greater than an electrolytic capacitor of similar size. When a secondary battery and an electric double-layer capacitor are connected in parallel, the electric double-layer capacitor floats at the same terminal voltage as the battery. The internal resistance of the electric double layer capacitor is very low, and the rechargeable battery is very high. When the load suddenly demands a large peak current, the peak current is supplied by the electric charge stored in the double-layer capacitor. Then, the battery charges the electric double-layer capacitor during a period in which the required current of the load is small.
[0011]
This fact has also been demonstrated in experiments with the circuit according to the invention. The maximum instantaneous change in the power supply voltage when a music signal was input to a digital amplifier having a maximum output of 2 W and driven by a 5 V nickel-metal hydride secondary battery exceeded 100 mV. On the other hand, when a digital amplifier is driven by connecting an electric double-layer capacitor of 17F (a value when three electric double-layer capacitors of 50 F are connected in series each) to a secondary battery, the same music signal is generated. It can be confirmed that the fluctuation of the power supply voltage is greatly improved to 20 mV or less. This means that a high-quality output faithful to the input signal can be obtained by sufficiently stabilizing the power supply to the power amplifier.
In addition, the fact that the fluctuation of the power supply voltage is small contributes to prolonging the life of the battery because the energy of the power supply is effectively transmitted to the power amplifier.
[0012]
Embodiment
Hereinafter, a low power consumption audio apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a main audio device 20 for transmitting an audio signal necessary for reproducing an audio signal and a cordless speaker system 10 according to the present invention. Reference numeral 21 denotes a CD player in the main audio device 20. The audio signal from the CD player is modulated by the infrared transmitter 22 and emitted to the speaker system 10 into space. On the speaker system side, the light receiving element of the infrared receiver 11 receives infrared light, and the original audio signal is demodulated. The demodulated audio signal is amplified by the digital amplifier 12 supplied with power from the power supply unit 13 and drives the speaker unit 14. Infrared signal transmission is possible with relatively low power consumption and is suitable for indoor transmission at home. In addition, the infrared receiver can reduce power consumption particularly, can operate on a battery, and has little effect on the power consumption of the entire speaker system even when shared with an amplifier power supply. Here, the wireless transmission using infrared rays has been described, but the present invention is also applicable to short-range wireless transmission using other electromagnetic waves.
[0013]
The reason why the power amplifier is a digital amplifier is that the power efficiency of the digital amplifier is higher than that of the analog amplifier. However, depending on the use of the reproducing apparatus, an analog amplifier with low power consumption can be used. Then, the digital amplifier 12 and the speaker unit 14 are combined with a digital amplifier having an output of several watts or less and a sound amplifier having as high a sound pressure sensitivity as possible so as to conform to the low power consumption of the audio reproducing apparatus which is the gist of the present invention. . Also, as for the speaker box, a speaker box having a high sound pressure sensitivity is preferably used, such as a back load horn that also uses the sound pressure from the back of the speaker unit. With these combinations, high sound pressure sensitivity can be obtained with a small amount of power supply.
[0014]
Reference numeral 13 denotes a power supply unit that supplies power to the digital amplifier. Reference numeral 13 is composed of a secondary battery and an ultra-high-capacity capacitor such as an electric double-layer capacitor, and can cope with a longer life and a rapid change in load. Nickel-metal hydride batteries have a low voltage of 1.2 V but a long life of 2 Ah to 7 Ah. In this embodiment, four nickel-metal hydride batteries 131 are connected in series to 4.8 V (actually, a voltage of 5 V or more is obtained), and three 2.3 V electric double-layer capacitors 32 are connected in series. Were connected in parallel. Then, three high-resistance resistors 133 are connected in parallel to the electric double-layer capacitors 132 connected in series so as to apply a voltage evenly. The voltage applied to the capacitor can be equalized not only by the above-described method but also by automatically setting the voltage between the terminals of the capacitor using a semiconductor switch and a comparator. Further, a higher rated voltage may be used. In addition, in order to supplement the high-frequency response characteristics of the electric double-layer capacitor, a high-frequency response capacitor 134 such as a ceramic capacitor compatible with the electric double-layer capacitor is connected to the power supply unit 13 in parallel with the battery. Note that the output voltage of the power supply unit has no special significance because the operating voltage of a commercially available digital amplifier whose output is about 2 W is adjusted to 5 ± 0.5 V.
[0015]
Note that the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention.
For example, the combination of the battery and the capacitor of the power supply unit can be changed depending on the intended use. As for the battery, not only a nickel hydride battery but also a secondary battery such as a lithium ion battery or a fuel cell, or a combination of a primary battery or a secondary thunder pond and a solar battery is possible.
[0016]
In addition, a power supply stabilization and voltage conversion circuit such as a DC-DC converter can be inserted between the battery and the capacitor for stabilizing and boosting the battery voltage.
[0017]
In addition, it also includes blinking or continuous or color change, character display, or warning sound by an indicator that notifies the outside when the charge amount of the battery decreases. In addition, the status of the speaker system can be notified to the main audio device through infrared or short-range wireless transmission, such as the status of the battery. It is a feature of the present invention to always provide a device that can perform two-way communication or one-way communication between the main audio device and the speaker system.
[0018]
FIG. 2 shows a second embodiment according to the present invention, in which blocks performing the same operations as those in the first embodiment are denoted by the same reference numerals as in FIG.
In the second embodiment, the effect of the present invention is further enhanced.
Many recent power amplifiers are configured by semiconductor element transistors. The transistor amplifier is basically a current drive type, and a maximum output is obtained when a low impedance load is connected. For example, when the power supply voltage of a commercially available digital amplifier IC having a maximum output of 2 W is 5 V, an output of 2 W is obtained when the load impedance is 4 Ω, and only an output of 1 W is obtained when the load impedance is 8 Ω. However, the power efficiency when the load impedance is 8Ω is better than when the load impedance is 4Ω.
The second embodiment of the present invention focuses on this point.
[0019]
The output of the digital amplifier 12 in FIG. 2 drives two speaker units 14 each having an impedance of 8Ω. Therefore, the load impedance of the digital amplifier 12 at this time is 4Ω, and the maximum output is obtained. However, when such a large volume is not required as in the case of background music, one speaker unit is disconnected by the switch 31 and the load impedance of the digital amplifier 12 is set to 8Ω. This has the effect of increasing the power efficiency when the normal volume is sufficient and extending the life of the battery of the power supply. In the above description, switching of two speaker units has been described, but it is apparent that the same object can be achieved by switching the voice coil of one speaker unit as needed.
[0020]
A method of switching the power supply voltage as needed for the purpose of increasing the power efficiency of the amplifier has been used for some time. However, the effect can be improved by combining the method with the load impedance switching method described above. The power supply unit 32 shown in FIG. 2 includes a nickel-metal hydride battery 131, an electric double layer capacitor 132, and a switch 321. The power supply voltage can be changed as needed. That is, when there is no input signal to the amplifier or in the second embodiment, if it is detected that the signal is not transmitted wirelessly, and the switches 321 are all turned off to cut off the power supply, further consumption of the battery will occur. And prolong the service life. At this time, if the electric double-layer capacitor is also disconnected from the power supply of the amplifier, the electric charge remaining in the electric double-layer capacitor is supplied only to a low power consumption circuit such as a display, so that the power supply can be effectively used.
[0021]
【The invention's effect】
As described above, according to the present invention, a battery cable provided in a speaker system and an electric double-layer capacitor are connected in parallel, and a signal cable and a power cable required for a conventional speaker system by wireless transmission of audio signals. There is an effect that the speaker system is completely cordless, and can be installed independently at any place.
[0022]
In addition, the electric double-layer capacitor has an effect that a commercially available small secondary battery can operate for a long time even with an overcurrent due to a sudden change in an audio signal. That is, there is an effect that a large volume is output from the speaker, the sound quality is maintained at a high sound quality, and the battery built in the speaker system can operate for a long time.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a cordless speaker system according to a first embodiment.
FIG. 2 is a diagram illustrating a configuration of a cordless speaker system according to a second embodiment.
FIG. 3 is a diagram illustrating a configuration of a digital amplifier.
[Explanation of symbols]
Reference Signs List 10 Cordless speaker system 11 Infrared receiver 12 Digital amplifier 13 Power supply unit 14 Speaker unit 20 Main audio device 21 CD player 22 Infrared transmitter 31 Load impedance switch 32 Power supply unit with switch 100 Digital amplifier configuration diagram 101 PWM modulator 102 Power switch 103 Low pass filter 131 Nickel metal hydride battery 132 Electric double layer capacitor 133 Resistance 134 High frequency response capacitor 321 Voltage switch

Claims (6)

A receiver for receiving an audio signal transmitted wirelessly,
A power amplifier that amplifies power,
A power supply circuit in which a secondary battery or a primary battery or a battery provided with a solar battery and a secondary battery and an electric double-layer capacitor are connected in parallel;
A cordless speaker system comprising: In claim 1,
A cordless speaker system comprising: a power supply circuit in which an electric double-layer capacitor and a capacitor having better high-frequency response characteristics than the electric double-layer capacitor are connected in parallel. In claim 1,
A cordless battery comprising: a secondary battery, a primary battery, or a battery having a solar battery and a secondary battery in combination, an electric double-layer capacitor, and a power supply circuit including a voltage stabilizing circuit or a voltage converting circuit. Speaker system. In claim 1,
A cordless speaker system comprising: a load impedance switch for switching a load impedance of a power amplifier according to a volume; or a load impedance switch and an amplifier supply voltage switch. In claim 1,
A cordless speaker system comprising a display for notifying the status of the speaker system or a transmitter for wirelessly transmitting the status of the speaker system to another system. In claim 1,
A detector for detecting an input audio signal;
And a switch for turning off a power supply line to the power amplifier, turning off a battery and an electric double layer capacitor when the detector detects that the audio signal has been lost, and discharging the remaining electric charge of the electric double layer capacitor. A cordless speaker system characterized by effective use.

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