Stretchable, Flexible, Transparent Nanotube Speakers

An anonymous reader writes "Chinese researchers have realised that a sheet of nanotubes behaves like a speaker when you send an audio current through it. The technology opens the way for a range of new versatile speaker systems. A video shows the speakers in action — some are stretched, one has even been sewn into a flag."

Re:Sound Quality/Better speakers

[pz]

Sigh. It's great that you're excited and all, but just because there's a new technology for turning electrical input into mechanical work doesn't mean it is an advance in speakers. For example, piezoelectrics were touted as the be-all-end-all for speaker design when they came out. But, it turns out, they are rather bad at being designed into speakers, and even then, they aren't that accurate (although there are certainly exceptions).

The fundamental problem in speaker design is the inescapable mismatch of mechanical impedance between the relatively solid (ie, low mechanical impedance) speaker and the relatively non-solid (ie, high mechanical impedance) air. Using horn loading helps this a lot (the best speakers I've ever hear were horn loaded) as this serves as a mechanical transformer between the speaker and the room air. But what helps more than anything else for a given amount of engineering effort and cost is doing all of the bandpass filtering well before the final amplification stage and having exactly one acoustic driver per amplifier output stage. (If you don't already understand the reasons for this, just ask, I'd love to tell you about them!)

Now, will a curtain of this nanotube stuff work as a speaker? Sounds probable. Will it work well? I doubt it, since to accurately reproduce sound, the actuating mechanism (ie, the cone in a conventional speaker) needs to be as rigid as possible so that the acoustic wave it produces accurately corresponds to the electrical signal delivered to it. Internal distortions in the actuating surface (waves on the cone of a conventional speaker, or on the surface of this nanotube stuff) distorts the output. The larger the actuating surface, the more important its rigidity (read: it needs an extremely low internal mechanical impedance).

The ideal sound source for reproduction is a physical point, not a sheet. The reason speakers have physical extent, rather than being points, is the coupling issue touched upon above: they need to have extent that is comparable to the wavelength they are trying to reproduce in order to have sufficient coupling to the atmosphere -- unless an acoustic coupling mechanism is used, like a horn.

Re:Sound Quality/Better speakers

[phantomfive]

That was an extremely interesting post, but these carbon-nanotube speakers are not vibrating at all! Read the article, they put a laser vibrometer on the thing, and didn't detect a single movement. Now, you have to admit that's pretty great. They think it is happening because of rapid oscillation of temperature, which is what happens with a thermophone. [answers.com] Which is an obscure little thing I had never heard of. They unfortunately don't mention anything about sound quality, but it at least matches youtube's! The idea of carbon nano-tube speakers is something I had not considered, but is definitely cool. I was actually, believe it or not, daydreaming about better headphone speakers last night. Not that I actually have any clue how to do it.

Re:Sound Quality/Better speakers

[ceoyoyo]

While it doesn't necessarily mean it will make a good speaker (the sound on the video sounded pretty bad, but that could be because of the music chosen, the recording, or the video player), but according to the article the mechanism of sound production is not mechanical. Most of your points are quite true when you're actually vibrating a solid to produce the sound, but don't apply otherwise.