Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1999-03-11
2003-07-08
Kuntz, Curtis (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S190000
Reexamination Certificate
active
06590992
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a speaker device, more particularly, to a speaker device used for generating music, for example.
2. Description of the Related Art
As a first example of a speaker device for generating music, a dynamic speaker includes a vibrator which is made of a cone of paper or the like and is vibrated using a voice coil and a magnet. In addition, a second example of a speaker for generating music is a capacitor speaker which is adapted to generate sound using an electrical charge.
However, the resonant frequency of such conventional dynamic and capacitor speakers is approximately 40 Hz~200 Hz, which is considerably lower than the upper limit of the human audible range, that is, approximately 20 kHz. Therefore, when music and other sounds are generated, sound at frequencies above the resonant frequency are necessarily generated. The motion of a vibrator which defines a speaker driving system is best at the resonant frequency, but there is a disadvantage that when a signal higher than the resonant frequency is input, the motion of the vibrator lags behind the input signal. Consequently, it is not possible to reliably and accurately generate sound in higher frequency regions, such as regions having a frequency that is higher than the resonant frequency. For instance, when humans actually listen to the sound of a drum, first the listener hears the sound of the stick strike the skin of the drum, and afterwards, the listener hears the sound produced by the vibrating skin of the drum. However, when this is generated on a conventional speaker, the fraction of sound when the stick strikes the drum is not generated, and a listener only hears the sound of the drum itself. It is believed that this is because, when a high-frequency signal at the moment when the stick strikes the skin is input, such a sound is not generated due to poor responsiveness of the vibrator, whereas the subsequently input low-frequency sound of the drum is generated.
Furthermore, a vibrator made of paper or similar material has a small mass and is easily influenced by outside pressure, whereby its acoustic characteristics are altered by outside pressure. Furthermore, when considering sound as energy, in a case where sound is generated by vibrating a low-mass vibrator, when a signal of large energy is input, the amplitude of the vibrator will increase, and as a consequence, sound pressure of the generated sound will increase. However, when sound pressure increases, the effect on the human body increases, which is unpleasant for the human listener.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a speaker device which is constructed to accurately generate sound at high audio regions and in which sound pressure does not increase when large sound is generated.
According to one particular preferred embodiment of the present invention, a speaker device includes a sound-producing vibrator having a vibrating body constructed to be vibrated by an input signal for producing sound from vibrations of the vibrating body and a signal input for applying the input signal to the sound-producing vibrator, wherein a resonant frequency of the sound-producing vibrator is higher than a frequency of the input signal.
Preferably, in the speaker device of preferred embodiments of the present invention, the resonant frequency of the sound-producing vibrator does not change substantially when the mass of the vibrating body is changed.
To obtain such a speaker device, the vibrating body can, for instance, be made of piezoelectric ceramic.
Delay in the vibration of the vibrating body relative to input signals having a frequency below the resonant frequency can be significantly reduced by increasing the resonant frequency of the sound-producing vibrator above the frequency of the input signal. Particularly, when the sound-producing vibrator has a resonant frequency higher than the upper limit of the human audible range of approximately 20 kHz, all sounds audible to humans can be accurately generated.
Furthermore, since the resonant frequency of the sound-producing vibrator is constructed so as to not be substantially altered by changes in the mass of the vibrating body, the mass of the sound-producing vibrator can be made large, and consequently, the effects of outside pressure on the sound-producing vibrator can be eliminated. In addition, even when a signal of great energy is input to the sound-producing vibrator, the sound pressure of generated sound can be reduced without increasing the thickness of the vibrating body.
Furthermore, the vibrating body may be made of piezoelectric ceramic, thereby increasing the mass of the sound-producing vibrator.
The above and further objects, characteristics and advantages of the present invention will more fully appear from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawings.
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M. Colloms, “High Performance Loudspeakers”, 5thEdition, 1997, Wiley, pp. 216-219.
Keating & Bennett LLP
Kuntz Curtis
Murata Manufacturing Co. Ltd.
Ni Suhan
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