JPH0221720B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulse code modulation reproduction speaker.

Conventionally, a speaker has been proposed that reproduces signals obtained by converting an analog signal into a digital signal using an acoustic converter that supports MSB to LSB. In this case, the number of acoustic transducers required for playback corresponds to each bit, which has the disadvantage of complicating the device, and when multiple coils are attached to the bobbin of one transducer, the conversion efficiency decreases due to the increased mass. It has the disadvantage of

The present invention provides a novel device which overcomes the above-mentioned drawbacks and is achieved by utilizing the non-linear parametric effects of air.

The present invention will be explained by way of an example.

FIG. 1 is a diagram showing an embodiment of the present invention. Input signal 1 is pulse code modulated by AD converter 2, and the signal is 4 bits. Signals 5, 6,
Shown as 7 and 8. The oscillator 4 includes ultrasonic elements 21 and 2
It has an oscillation frequency approximately equal to each of the resonance frequencies of 2, 23, and 24. The signal of the oscillator 4 and the signals 5, 6, 7, 8 are multiplied by the multipliers 9, 10, 11, 12.
Perform calculations with .

The processed signals are sent to amplifiers 13, 14, 1
5, 16, level control element 1
At steps 7, 18, and 20, weighting is performed according to each bit.

By applying a signal to the ultrasonic elements 21, 22, 23, and 24, the resonance frequency of the ultrasonic element and the reference frequency included in the signal In this embodiment, the frequency of the oscillator 4 is set to be approximately equal. Next, the signals of each part will be explained with reference to FIG.

When waveform a of input signal 1 is sampled as shown in C and AD converted, signals 5, 6,
7 and 8 respectively have LSB as b ₁ and b ₂ , b ₃ and
It is converted into a 4-bit parallel signal with the MSB as _b4 . On the other hand, the ultrasonic frequency sine wave signal d from the oscillator 4
is output and processed by multipliers 9, 10, 11, and 12 to obtain signals of d ₁ , d ₂ , d ₃ , and d ₄ at the respective outputs.

When weights are applied to the ultrasonic elements 21, 22, 23, and 24 of the acoustic transducer with weights depending on the respective bits, when the sound waves from each element are radiated in phase, the air vibrates in a waveform e.

If the envelope line of the sound wave is g(t), this waveform (t) is expressed as (t)={1+g(t)}coswt.

where is the resonant angular frequency of the ultrasonic element.
This sound wave generates a secondary sound pressure of P(r,t)=K∂ ² /r∂t ² g(t−r/c) due to parametric action.

However, γ is the distance between the ultrasonic element and the sound receiving point, c is the speed of sound, and K is a constant determined by air density, nonlinear constant, etc.

It is easy to understand that g(t) is a sine wave like a, but the secondary sound wave is the envelope g(t) of e. g
If we ignore the harmonic components of (t), the waveform we hear will be as follows. This is equal to the original input waveform a.

However, the amplitude modulation index shown in this case is considered to be 1. What is the best way to make this smaller?
It is sufficient to emit sound waves of only ultrasonic components from one or all of the ultrasonic transducers, and it is sufficient to separately provide an ultrasonic transducer for this purpose.

In addition, level control elements 17, 18, 1
Ultrasonic element 2 without using weighting by 9, 20
It is also possible to use input characteristics 1, 22, 23, and 24 that correspond to the respective bits.

Since each bit is arranged in parallel for acoustic conversion, a vibrating element with a high resonance frequency can be obtained. It is also possible to create and modulate an ultrasonic vibration frequency through arithmetic processing that matches the resonance frequency of each acoustic transducer element.

FIG. 3 is a diagram showing another embodiment of the present invention, in which the outputs of multipliers 9, 10, 11, and 12 are weighted, combined in an adder 34, amplified in an amplifier 33, and to convert the sound. In this case, only one amplifier can be used.

FIG. 4 is a diagram showing another embodiment of the present invention, and shows a configuration in which the signal from the oscillator 4 is level-adjusted by a level control element 36 and added to the adder 34 as a bias component in the configuration shown in FIG. 3. .

Since the level is adjusted by the level control element 36, adjustment using a single element is possible when adjusting to the non-linear characteristics of air.

The ultrasonic element 35 may be a single element or may be composed of an array.

Although the above explanation has been made using 4 bits, it is also possible to increase or decrease the number of bits.

As described above, according to the present invention, by reproducing a pulse code modulated signal with an ultrasonic element, it is possible to reproduce sound using the nonlinear parametric effect of air.

[Brief explanation of drawings]

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a diagram for explaining waveforms of each part, and FIGS. 3 and 4 are diagrams showing other embodiments of the present invention. . 1... Input signal, 2... AD converter, 4... Oscillator, 5, 6, 7, 8... Signal, 9, 10, 1
1, 12...multiplier, 13, 14, 15, 16,
33...Amplifier, 17, 18, 19, 20, 36
...Level control element, 21, 22, 2
3, 24, 35... Ultrasonic element.

Claims (1)

[Claims] 1. An AD converter that AD converts an input signal, a multiplier that multiplies the AD converted parallel signal by a frequency approximately equal to the resonant frequency of the electroacoustic transducer, and the multiplied parallel signal, respectively. It is equipped with a weighting means, an adding means for adding weighted parallel signals, and an electroacoustic transducer that inputs the added signal to an electroacoustic transducer and converts it into an acoustic signal, and utilizes the nonlinear parametric action of air. What is claimed is: 1. A pulse code modulation signal reproducing device which obtains reproduced sound using a pulse code modulation signal. 2. The pulse code modulation signal reproducing device according to claim 1, wherein the weighted parallel signals are input to each electroacoustic transducer and the adding means is a reproduction sound field.