• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

building a "sound beam" device

Not open for further replies.


New Member
I am working on a project called "parametric array". It's a device that makes sound to be very directional. If you want to learn more about it you can visit the site: http://www.atcsd.com/tl_hss.html
Actually to have the directionality effect, you have to mix an ultrasound signal to the audible sound you want to transmit. I realized an Amplitude Modulation circuit using as a carrier a 38kHz sine wave and as a signal 1kHz sine wave.

My college had the ultrasonic emiter given by ATC for a demo. So I just had to match the emiter to an amplifier. I have been told by ATC that my emiter had a 160nF capacitance and a 2 Ohm resistance. I built a 8W amplifier and plugged an inductor of 150µH in series with my transmitter to compensate the capacitance of the emiter.

That went good, I had quite a low volume but I could hear that the device produced very directionnal sound. :)

I am now trying to plug it on an audio 50W amplifier. I firstly checked that my amplifier (Rotel RA931MkII) worked good at frequencies as high as 60kHz (pluggin it on a 4Ohm resistor and studying voltage vs. frequency). That was ok.

Then I tryied it on my emiter.To be more cautious, I plugged a 4Ohm resistance in series with the inductor and the emiter. But, when I tried to make it work, the voltage at the output of the amplifier didn't go above 1V (with 1V input) and the amplifier began to spread roasted components smell :roll: so I turned it off...

Do you know something that could help me in understanding my problem?




New Member
Audio amp works upto 60kHz ?

I am amazed :shock: that your audio amp (the Rotel RA931MkII) can cope with ultrasonics ??

I wonder if the complex load of the emitter and series resistor could be causing something like an SWR - reflecting power back into your amp and causing the output transistors to dump all this reflected power as heat.
{>> This is a GUESS <<} but you must admit you are way beyond the amp's design parameters :!:
The only other thing I can think of is that the Rotel amp's output stage is actually destroying itself as one transistor starts to conduct before the other stops (as the signal passes through quiescent) - maybe some internal flywheel effect that isn't a problem at audio frequencies {but I suppose this should be evident with your test load resistor as well?}

Given that you are still in development here I would suggest building your own simple power amp - no audio bandwidth compensation, no equalisation, no bells, no whistles - just BASIC.
A simple op-amp input stage and very simple power transistor output.
This will at least let you disprove my guess of SWR problems ?


New Member
Thanx a lot for your reply, mechie.

I am now building this power amp I will give you some news when it will be done


Not open for further replies.

Latest threads

EE World Online Articles