JPH0311160B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention is based on PCM (Pulse Code Modulation).
The present invention relates to a digital speaker applied to a reproduction device for converted audio signals.

In recent years, in the field of audio equipment, by converting audio signals into PCM and handling them, it has become possible to improve the S/N ratio, expand the dynamic range, and
PCM conversion of audio signals is being actively adopted due to various possible benefits such as reduction in non-linear distortion.

By the way, in order to digitize an audio signal waveform, which is an analog signal, according to the sampling theorem, two of the highest frequencies contained in the audio signal are
It is known that it is sufficient to perform sampling at twice the repetition frequency and convert the sampled value into a binary code, but in order to recover the original audio signal from this binary code, it is necessary to It is necessary to provide a D/A conversion function to the path.

The present invention relates to a digital speaker that can perform such a D/A conversion function in an acoustic system.

Figure 1 shows one method of acoustically D/A converting a PCM audio signal.
PCM signal sources 12 ₁ to 12 _K are k-bit binary code signal lines output from terminals T ₁ to T _K , and each signal line 12 ₁ to 12 _K has audio signal sampling values as shown in the figure. Parallel bit signals in the form of binary codes are sent out at sampling intervals. 13 ₁ to 13 _K are output amplifiers, 1
4 ₁ to 14 _K indicate speakers. By the way, various types of binary codes can be considered as the binary code supplied as the parallel bit signal. For example, when the number of quantization levels is 10, a 4221 code, and when the number of quantization levels is 16, a 4-bit code such as an 8421 code is possible. However, in order to increase the dynamic range, a large number of quantization levels must be set, and the number of bits k of the binary code increases accordingly. However, in any case, each bit constituting the binary code is considered to be a signal with a weight for each bit digit. In the case of FIG. 1 as well, the output amplifiers 13 ₁ to 13 corresponding to each bit
13 _K is set to output a signal proportional to this weight and drive the speakers 14 ₁ to 14 _K. Then, the sound pressure generated at a point P equidistant from each speaker 14 ₁ to 14 _K is
Since this is the sum of the sound pressures emitted by 4 ₁ to 14 _K , at this point P, the sound pressure obtained by quantizing the sampling value of the original audio signal is restored. Therefore, when the sound pressure is listened to at this point P through the high-frequency cutoff acoustic filter, the original audio signal that has been D/A converted will be heard.

By the way, with such multi-unit digital speakers, the service area where you can hear the audio signal is the area where all speakers 1
The signal is limited to a point P equidistant from 4 ₁ to 14 _K , and at other points Q and R, of course, only distorted audio signals can be heard, resulting in degraded S/N ratios.

This invention was made in view of the above, and is directly driven by a PCM audio signal, and the speaker itself has a D/A conversion function, so that the original audio can be reproduced regardless of the listening area. This allows the signal to be reproduced.

FIG. 2 shows a partially sectional perspective view of a digital speaker according to an embodiment of the present invention, in which 1 is a speaker box, and 2 is a partition that divides the inside of the speaker box 1 into two. The plates 3a to 3e are direct radiation type speakers attached to the partition plate 2, 4 is a diaphragm, and 5 is a free edge of the diaphragm 4.

Next, to explain its function, the speaker box 1 is divided into two by the partition plate 2 into a rear chamber V ₁ and a front chamber V ₂ , and the rear chamber V ₁ is used for the speakers 3 a to 3 e attached to the partition plate 2 . Forming a closed space that becomes a battle,
The front chamber _V2 forms a sealed acoustic space in which D/A conversion, which will be described later, is performed. The number of speakers 3a to 3e attached to the partition plate 2 is not limited to five.
It is installed corresponding to the number k of binary code bits of the PCM signal, and generates an acoustic output proportional to the weight of the bits of the binary code, similar to the multi-unit digital speaker shown in Figure 1. This kind of acoustic output is similar to the first one mentioned above.
Similarly to the figure, the power of an amplifier (not shown) that drives the speakers 3a to 3e may be set.
Further, the speakers 3a to 3e may have different electrical-acoustic conversion efficiency. Also, the front room
The diaphragm 4 supported by a free edge 5 provided on the side wall of the front chamber V ₂ is displaced according to the sound pressure inside the front chamber V ₂ , and the diaphragm 4 is a passive radiator that emits the change in sound pressure outside the box body. It is something that forms.

In the digital speaker of the present invention having such a configuration, when the speakers 3a to 3e are driven by PCM parallel binary codes (not shown) as in FIG. 1, the acoustic pressure emitted from each speaker 3a to 3e is sealed. It is added in the vestibule V ₂ that forms the space. That is, at a certain point in time, a composite sound pressure of the speakers 3a and 3e is generated in the front chamber _V2 ,
At the next point in time, a composite sound pressure from the speakers 3b, 3c, and 3e is generated in the front chamber _V2 . As a result, the resultant acoustic pressure in the vestibule V ₂ is proportional to the amplitude value of the sampled audio signal. Therefore, the D/A converted sound pressure is released to the outside by the diaphragm 4 which is displaced in proportion to this sound pressure, so the original audio signal can be heard at any point outside the box. You will be able to

Note that the high frequency blocking acoustic filter that suppresses quantization noise caused by quantization during conversion to a PCM signal is related to the mass and stiffness of the diaphragm 4 (including the free edge 5) and the volume of the front chamber _V2 . By appropriately determining compliance, the digital speaker itself shown in FIG. 2 can be made to have compliance, but as _shown in FIG. ₃
A sound-absorbing material 7 may be provided in the aperture 6 to constitute a high frequency blocking acoustic filter to emit only audio acoustic waves to the listening service area.

Further, the diaphragm 4 may be considered as a sound pressure radiation surface without a driving point, and may have a structure in which a flexible diaphragm is stretched, for example, and the number and arrangement of the speakers 3a to 3e and the area of the diaphragm may also be It can be designed as appropriate depending on the input PCM signal.

FIG. 4 shows another embodiment of the present invention, in which the direct radiation type speakers 3a to 3e shown in FIG.
Instead, horn speakers 8a to 8e are provided. It goes without saying that the number of horn speakers is determined by the number k of parallel bits of the PCM signal.

This embodiment does not require a full plate due to the characteristics of the horn speaker, so the rear chamber formed as shown in Fig. 2 is used.
The operating principle is the same as that of the digital speaker shown in Fig. 2 above, except that the one corresponding to V ₁ is no longer needed, and its explanation will be omitted, but compared to a direct radiation type speaker, ( 1) Since the horn speaker uses a dome diaphragm and has high acoustic impedance when viewed from the outside, the acoustic pressure emitted from the horn speaker 8a, for example, does not affect the other horn speakers 8b to 8e.

(2) Since a full board is not required, the mounting position of each horn speaker is not limited, and the number of horn speakers to be mounted can be easily increased.

It has this special effect and is suitable for use as a digital speaker.

As explained above, the digital speaker of the present invention can be directly driven by a digital signal obtained by converting an audio signal into PCM, so an electrical or mechanical D/A converter is not required in the reproduction system, and Since the reproduced audio acoustic waves can be generated from a diaphragm in the same way as a normal analog speaker, the listening area has the advantage that it can be expanded to any three-dimensional point.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a multi-unit type digital speaker, FIG. 2 is a perspective view of the digital speaker of the present invention, and FIGS. 3 and 4 are side views showing other embodiments of the present invention. . In the figure, 1 is a speaker box, 3a to 3e, and 8
A to 8e are speakers, and 4 is a diaphragm.

Claims (1)

[Claims] 1 A speaker box which is divided into two halves so that at least one side is sealed with air by a partition plate, and a speaker box which is attached to the partition plate and which is supplied with a digital signal corresponding to each bit of an audio binary code. 1. A digital speaker comprising: a plurality of speakers; and a diaphragm supported by a free edge on a wall of the sealed air chamber formed on the front side of the plurality of speakers.