The materials used to make speaker diaphragms are well establishedpolypropylene, paper, Kevlar, aluminum, titanium, beryllium, silk, and even diamond, to name a few. So I was surprised to find a speaker system with diaphragms made of glass. Developed over nearly four years by a Japanese glass company called Hario (Japanese for "king of glass"), the Harion system is certainly intriguing, though the English-language website linked here has nothing about it, and the company did not supply much info, even after repeated requests.
The 2-channel system consists of a downfiring subwoofer pictured here, two midrange modules that fire upward into a 360-degree reflector, and two direct-radiating tweeters, all of which are separate modules. The sub and midrange diaphragms are fashioned from heat-resistant, borosilicate glass a mere 0.8mm thick, while the tweeters are actually made from acrylic. I received no answer to my question about why acrylic was used in the tweeter, but I suspect it could be because glass might shatter at high frequencies.
How much does the Harion system cost? The company hasn't answered that question yet. Hario does say it spent 16 million yen ($174,000 as of this writing) to hand-build one set, so if it ever becomes a commercial product, it won't be cheap.
How does it sound? I have no idea, but I'm skeptical, especially since the company's main business seems to be making glass teapots and other housewares. Hario claims that glass is highly moisture resistant and very stiff, allowing it to produce "powerful low-range sounds." I'm not at all sure about that, but the proof is in the hearing, and so far, the Harion has only been demonstrated in Japan as far as I know. I'm not saying this idea will result in sublime sound, but it sure is interesting nonetheless.