Berkeley creates the first graphene earphones
extremetech.com
extremetech.com
Without the bias voltage, there would be no electric bias field between either electrode relative to the diaphragm, against which bias fields the signal adds or subtracts in order to move the diaphragm bidirectionally.
The required bias voltage of an electric field headphone element (or speaker) is very much akin to the permanent magnet of a conventional electromagnetic loudspeaker -- both provide a fixed field against which the signal works to produce proportionate mechanical motion.
Whether this bias voltage requirement will eventually result in "phantom power"[1] on analog "headphone outputs" as it has [optionally] for professional analog microphone inputs[1] -- or small power cells and inverting electronics in the headphones or on the headphone wires (perhaps supporting other analog or DSP functions such as active noise cancellation, equalization for flatter response, or decryption of an encrypted digital headphone signal) -- may be up for the market's consideration in a few years.
Headphone drivers are very close to your ears which causes frequency dependent effects. Also there are issues with how the sounds bounces around your ears / ear canal / head in general (google Head Related Transfer Function for more).
A 10db drop between about 1khz and 20khz is 'about right' for a flat response during use. Additionally roll off on the low end is also expected in a measurement like this for in-ear headphones, a large amount of gain will be added once these are sealed in your ears.
That said, I'm complaining about the article, not the research. By all means, Berkeley researchers, please continue developing graphene earphones!
(We still don't have decent displays; all of them are flat, and most of them look terrible)
The problem in reproducing it exactly resolves to the problems of materials engineering and efficient coupling of your transducer to the air.
Meanwhile, your brain is doing an amazing job of extracting information from two point signals separated by the width of your skull. There's information that comes from the way that the shape of your ears distorts waves coming from different directions; timing information between the two ears; tilt information from kinesthetics and eyes. All that is handled by systems with a hundred million years or more of evolution in the Earth's biosphere, plus learned updates from your measly few years of life.
And 16 bits per sample, 44.1KHz sampling rate, will suffice to record it all as well as your ears can hear in any sort of normal environment. (A few more bits will suffice if you intend to capture both jet engines and soft breezes in the same recording.)
[0] http://www.genelec.com/products/dsp-products/glm-software/ [1] http://www.youtube.com/watch?feature=player_embedded&v=k...
Seriously though, graphene is super cool. Did anyone else notice that the "wave guide" looks suspiciously similar to a barrel type piece of Lego?