Last week, we explained the difference between $US100 and $US100,000 speakers. But in the name of clarity, we focused on traditional loudspeakers, around longer than Keith Richards. Here are the newer crazier types.
Alright, so the way speakers generate sound is by moving air. In your standard setup, an alternating current runs through a voice, turning it into an electromagnet that is attracted to and repulsed from the permanent magnet in the driver, which moves the diaphragm (the cone) back and forth. Air is moved, sound is emitted.
But magnets aren't the only way to generate sound, obviously. Here are a few other ways speakers can get air a-shakin':
Electrostatic speakers are probably the most well-known alternative to traditional loudspeaker design. In some ways, they're a lot like your standard speaker—a diaphragm moves back and forth. What's different is the shape of the diaphragm and how the system makes it move.
The diaphragm is a thin film with electrically conductive material that's stretched out between two conductive plates called "stators"—perforated steel sheets in Martin Logan's speakers—coated with an insulator. Just as the voice coil in a regular speaker is turned into an electromagnet by a current, the diaphragm and stators here are charged, creating an electrostatic field. As the charge alternates between positive and negative the diaphragm moves back and forth, generating sound. The stronger the charge, the more dynamically the diaphragm moves, and the louder the sound.
The claimed advantage of electrostatic speakers is that the entire diaphragm is driven, not just the apex, like with a standard voice coil/cone setup, so not only do you get improved frequency range, you won't get distortion from the diaphragm flexing. The flip side is that bass can be kinda weak—though size helps—and high volumes can pose some issues, given that the strong charges required for high volumes increases the chance for "pyrotechnical electrical discharge" (in other words, electrical fire). Oh, and they're not cheap. But they can sound pretty good!
Plasma speakers aren't new, but they are badass, and you can build your own. Or you know, just pay a lot of money to get some. The basic principle is, same as always, moving air. Except, instead of magnets or an electric field, a small electrical arc is manipulated, producing different pitches and volume as the intensity is shifted. Maybe not the future, but putting the word "plasma" into any tech just makes it sound future-y.
Distributed Mode Loudspeaker
Distributed mode loudspeaker tech was developed by NXT. It's different from your standard diaphragm tech because traditional speaker diaphragms have to remain rigid. They vibrate but they don't bend, because that causes distortion. Distributed-mode diaphragms are supposed to bend. Basically, bending waves are produced in the panel by electricity, and those vibrations create sound.
One big advantage of distributed mode loudspeakers is that they can be really thin. You don't need a big box. In fact, NXT's big pitch is that almost anything can be a diaphragm—in 2002, somebody actually tried to market inflatable speakers based on NXT's tech. But like other loudspeaker alternatives, it can have trouble with bass. A bigger panel helps it out there, however. Warwick Audio's suspiciously tinfoil-like new flat, flexible loudspeaker technology actually sounds similar in principle to NXT's DML—a thin membrane is excited and vibrates in time to the electrical signal.
Hey look, it's another technology using a thin membrane to move air! Planar magnetic speakers use a thin film with a voice coil printed on it (think back to traditional speakers). The coil is suspended between a pair of magnets. As the current alternates, the membrane moves and back forth. As with most of these thin-diaphragm setups, you need to go bigger to get a better bass response, or just go with a separate woofer for low frequencies. Oh, and they also cost lots o' dollars.
Carbon nanotubes, the trendiest near-future material around, can of course be used to make speakers too. Really thin ones. They actually work very differently, too. Nanotube speakers make use of thermoacoustics, just like thunder. The nanotubes are formed into a film with electrodes attached at the end. An electrical current is sent through the film, and as it changes, the air around the tubes heats up or cools down in response, expanding and contracting respectively. Pressure waves are created, and boom, sound. The fidelity supposedly "matches that of conventional loudspeakers." The nanotubes themselves don't move at all, meaning that technically, if the technology were harnessed, it could be used to make high-precision, super-low-distortion speakers.
But here's a really brilliant idea for future speakers that'll blow you away: Make 'em cheaper without getting crappier. Now there's innovation!
Still something you still wanna know? Send any questions about speakers, the future or the Numa Numa kid to [email protected], with "Giz Explains" in the subject line.