A parametric speaker
This kit is designed to be able to make the
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
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
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.
click for enlarge
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.
You can buy from eBay store HAMshopJapan
You need 15V to 25V DC power.This kit is experiment purpose only.
from case is minus
lead into circle rand,minus lead into rectangle rand
keep the whole unit so that it is parallel.
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