You might be thinking of plasma tweeters. Back in the late 70s/early 80s. 10K1980$ a pair. Just tweets.
They had a gas flame that was made to generate sound with an electric field.
You may be thinking of Hill Type 1 Plasmatronics that were $10k a pair back in the late 70s. The tweeters were both amazing and possibly hazardous to your health due to the ozone emitted into the room. The sound from the other drivers in the speakers couldn't keep up with the tweeters, though, especially the woofers. And unfortunately the tube amps built in to drive them were horribly unreliable, and each speaker had a helium tank you would have to get filled once in a while. Not to mention cosmetics that made them look like cobbled together lab equipment, not something you would put in your living room.
Note: Typical electrostatics already have membranes that weigh less then the air they're moving.
Your dog _might_ be able to distinguish between plasma and normal electrostatics. Not that electrostatics are exactly cheap or small.
Electrostatics that do real bass are by necessity large due to dipole cancellation. I own and sell Sound Lab electrostatics, which are some of the largest and most expensive of their type. While I will admit that a full range plasma speaker could potentially outperform an electrostatic, almost no full range plasma speakers have ever been built. In 1992 a French company showed a prototype full range cold air plasma speaker at the Consumer Electronics Show, but it never saw the light of day and the company went out of business. Nelson Pass of Threshold and Pass Labs had a full range plasma speaker but had to dismantle it due to the large amounts of ozone produced.