Here’s the full post from Nelson:
The "ion cloud loudspeaker" used photocopy
machine ionizing nichrome wire strung in a flat
array a bit like a window screen, but with more
space between the wires, and charged to a variable
DC potential of about 10 KV.
This screen developed a layer of ionized air, and was
enclosed between two stators, much like an electrostatic
speaker, except that instead of a charged plastic diaphragm,
you had a charged semi-flat layer of gas, and you could
push-pull it with high AC voltages on the stators.
It worked fairly well, and gave new meaning to the word
"transparency".
It also had several flaws, one of which did result in a
trip to the local emergency room with breathing problems
similar to those sometimes experienced by arc welders and
caused by extended exposure to ozone.
The Wall Street Journal printed my comment:
"It was the perfect high end audio product: Exotic, inefficient,
expensive, unavailable, and toxic."