Highly Directional Audio Paper?

I can't help you with the paper. However this technology is no new. The high intensity ultrasound is modulated by amplitude. It is demodulated in the air due to the thermal nonlinearities, so you can hear the sound. The main problem is that the required intensity of the ultrasound is too high to meet the safety requirements. So this technology can't be deployed for the general purpose use.

Vladimir Vassilevsky DSP and Mixed Signal Consultant

Don't know about that paper but you might also check out: <

Later...

Ron Capik NJ Pinelands Cultural Society <

it might be available from aes.org, but they may take money from you for downloading articles

martin

Although I have not read it any detail, there is a Wikipedia article on Parametric Loudspeakers.

It should not be surprising that high intensity ultrasound can generate audible difference frequencies. Unfortunately, the nonlinear mathematics required to describe a nonlinear process is complicated and non-intuitive. While at first blush this complexity is a deterrent to working in the field, it leaves much opportunity for invention and novelty.

Bill

Sorry; we need a journal reference.

But I recognize it as "parametric sonar". It took me a while to resolve what is being talked about since authors use different terminologies for the same facts.

Two ultrasound beams from the same sender cross at some remote point in space. Both beams are amplitude modulated with the same audio signal. The ultrasound ampitude of the combined beam is locally doubled such that nonlinear presssure vibrations occur at the modulated audio rate, whereby audible sound emerges in the coss beam zone. That audio is a traveling wave, and the wave propagation direction is the same as the ultrasound beam. So in effect, a wave of audble sound has been generated with very specific directionality; the same as that of the ultrasound beams that formed the audio.

A lot of seculation and half-truths have emerged since the invention of parametric sonar.

The human imagination provides wonderful entertainment...as is evident in the following words:

and they all lived happily after.

Ang. C.

I note a bit of sarcasm in your response :-). But there does seem to be real end users of the product. See

why not..

This particular non-linearity, aka cross modulation, is a progressive effect, with the greater nonlinearity occurring at the greater distance before diminished amplitude reverts to linear propagation, before vanishing.

The original concept, ancient history now, used crossed or crossing beams at first, if for no other reason than simplicity and the availability of powerful transducers, I think.

This is now out of research and into the production engineering and the market development phases.

Ang. C.

They can't afford good sound deadening foam to line their foil beanies.

Oh, hell - I thought you were talking about a piece of paper which, when you apply a signal, emits sound. )-;

Thanks, Rich

Well Rich, I did think about rephrasing the subject line, but looks like the idea got through. :-) Mike

Invented? His technical education was at RPI, a researcher at BOSE since the age of 16, MIT multimedia lab last.

In that case, he could not have invented the basic technology (production of audible sound from the nonlinear mixing of two ultrasonic sound sources), which was used to produce audible narration and music apparently in mid air with no visible source in the General Electric display at the 1964 worlds fair.

You can get the basic physics and math for this old technique in 'Fundamentals of Physical Acoustics' by Blackstock if you are interested. It is only one of many interesting effects produced by the inherently nonlinear characteristics of the propogation of finite amplitude sound through a gas. Sound propogation through liquids is also nonlinear, so the same thing could be done underwater.

Glen

Oopps! Sorry I didn't provide a smiley to indicate that my saddy was intended to be humourous. ;-)

Cheers! Rich

Rich, I'm fine with you, I get your humour, sometimes I even enjoy it :-) Mike Here's a smiley face to make up for the one you think you missed :-)

That looks like a good one. Thanks for the tip, Glen.

Hey, one is infinitely more than zero. ;-D

Thanks! Rich