You can enjoy super directivity

A parametric speaker experiment kit
Ultrasonic Directive Speaker

This kit is designed to be able to make the parametric speaker which used a supersonic wave easily. The parametric speaker uses distortion of supersonic wave which advance in the air, and it is structure reproducing a sound in the audio domain. This kit use DSB modulator. It is not performing the distortion such as the commercial parametric speaker. Therefore, please consent not to be suitable for listning the music.
This movie is demonstration of development modulator.DSB and FM Mixed Modulator.

Now, parametric speaker is driven by D class amplifire. Sound quality is better than DSB modulator.  2009.12.8
My parametric speaker is written in articles of Elector Magazine.
Now, parametric speaker is driven by D amp with delay timer 0.3sec max. 2012.11.13

The structure of the parametric speaker

The parametric speaker is the speaker which realized very sharp directivity using the going straight characteristics of the supersonic wave. It is said that the human hearing can hear a sound wave to about around 20kHz, but actually it is known for the frequency that is considerably lower than 20kHz not to hear. It depends on age, but it may be said that around 14kHz are the one that they should hear to the utmost.

The element to generate a supersonic wave uses a pressure electric phenomenon to be called piezoelectric element. With the kit, I use a supersonic wave transducer with the peak for 40kHz. Because the mountain of the peak is steep, It cannot let pass the too wide band. A normal human being cannot hear the supersonic wave of 40kHz at all.

Some methods to convert a supersonic wave into the sound wave that a human being can hear are devised. The one is a method to reproduce a sound of the frequency equal to the difference of the supersonic wave using two different supersonic waves source of the frequency. For example, a sound of 1kHz equal to the difference is known as undulation when it give a supersonic wave of 40kHz and 41kHz. I use a supersonic wave of 40kHz as a carrier wave, and AM is to give an irregular supersonic wave, and the neighborhood where two supersonic waves intersect can generate the sound of the audio domain from the other speaker. Because it is necessary for this method to continue giving a supersonic wave in a case without the signal consistently, an inefficient thing is a fault.


DSB is irregular, and, as for another method, distorted which produces the whole air when a supersonic wave goes uses a supersonic wave, and it is a method to reproduce the sound of the audio domain. The left image expresses the wave pattern which did switching of a voice signal at 40kHz. The inclusion line of this wave pattern (a line linking the top) is known as a distortion in the air.

DThat DSB modulation is amateur radio communications is an abnormality method used well. It is this kit and realizes a parametric effect using DSB abnormality by the analog switch.



The DSB modulation method has good efficiency, but there is a fault that sound quality is bad because it use distortion by the spread of the air. An original sound reproduces audio system spotlight and HSS with digital code processing after having been warped and prevents the deterioration of the sound quality. Because this kit do not work to such as commercial product, it is not suitable for listning music.

The schematics of the kit

In the circuit, it is constituted modulation circuit with an analog switch in the low pass filter which used op-amp. The amplifier part used AB grade amplifier of Toshiba, TA8258HQ. It is working at 15V - 35V, and there is the output of 20W at the maximum. With the kit, it works at 15V - 24V. IC become considerably hot when operating at 24V.

This schematics is a circuit used well with a transmitter of the software radio. Only one signal driving an analog switch is different from an output part being an audio system in a point (there is the IQ signal on the software radio).

The supersonic wave speaker to output used a transducer of a diameter of 10mm that sold by an Akizuki electron by the trial manufacture, but used a type of 16mm because it was small, and size was not efficient.




right click for enlarge image
THIS SCHEMATICS IS UNDER GPL.

The distribution of the kit

I start the distribution of new kit. This kit is introduced on articles of Elektor Magagine.
ソリューション画像


  • PWM modulator board + supersonic wave speaker (50pcs) $102USD*

  • You can buy from eBay store HAMshopJapan
    .
    You need 15V to 25V DC power.This kit is experiment purpose only.



Speaker PCB


lead from case is minus

plus lead into circle rand,minus lead into rectangle rand

Can keep the whole unit so that it is parallel.


using transformer.If you do not use transformer, both solder jumper is ON.
If the sound level is lower when DC power is under 20V, you should use transformer or inductor.Using transformer case, it is suitable 800ohm:8ohm like SANSUI ST-83.white lead and green(8ohm) lead to output of modulator,white and red(800ohm) to speaker PCB.capacitor is 0.47uF 50V.please see schematics of speakers.



You can use inductor another way.Please put 80uH to 100uH inductor in series to speaker.
Kit may includ Ferrite bar. you need winding about 30 times with magnet wire.


right click to enlarge images
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