John Iversons ultrasonic speakers?

This is not quite a DIY question, although some might be
tempted to give it a try perhaps :) .

This became quite a lengthy post, so I take the question before
the background. Does anybody know what became of this
project or have any further info (links, references etc.)?



Back in the late 70s I read an article in the swedish magazine
"Radio&Television" about a pair of strange speakers designed
by John Iverson. As I remember it the principle was to modulate
the signal onto a 300kHz carrier frequency, amplify this (using
multi-kW HF amplifiers !!) and then use two parallel vertical
metal bars as the "speaker element". Presumably the carrier
frequencies for the two bars were modulated with the signal
180 deg. out of phase in one case.

The interesting thing about these speakers was that they
bypassed the mechanical system of the ear, since such high
frequencis can only be detected by bone conduction through
the skull. It seems the difference signal, ie. the original signal,
was somehow detected by the nerve centres in the ear.
On the good side, the journalist claimed these to be the best
speakers he had ever listened to - the sound was claimed
fantastic, probably because the mechanical distorsion in the
ear was avoided. Many (but not all) deaf people could hear
such speakers. The drawbacks were very low efficiency and
all the problems with HF amplification, an extremely narrow
radiation angle (moving your head about 10cm to the side
would make the speakers sound silent) and the potential
health hazards.

The reasons I am asking here at DIYaudio are
1) There seems to be lot of people who have been in this
business for a very very long time, and some ought to
remember this.
2) While mining deep into the archives for something else I
found a post by Harry Haller, mentioning that Iverson
disappeared somewhat mysteriously a while back. This gave
me the idea to ask here.
 
koen said:
Somewhat related is this article on hypersonic sound. Pretty interesting stuff.

http://www.popsci.com/popsci/science/article/0,12543,351353,00.html

Interesting indeed. Did you understand it? I found it a bit too
popular and void of details to be understandable. I assume
we have the signal modulating an ultrasonic carrier also in
this case, althought probably not so high carrier frequency.
But then? It seems the audible signal is somehow detected
by distorsion in the air so that an ordinary audible signal
finally reaches the ear. Is this how you understood it too?