Traditionally, hearing aids are available with “T-coil compatibility”, which allows certain things, like compatible telephones, to electromagnetically couple with the electronics in the hearing aid, rather than taking the tiny, noisy audio signal from a phone speaker, sending it through an airgap polluted with ambient noise, and into a microphone, and then into the headphone’s circuitry. The idea is there’s a voicecoil in the speaker anyway, and an EM field is driving it, why not pick up the electromagnetic flux in the hearing aid with a loop of wire and feed that to the amplification circuitry?
This has been expanded so that a loop of wire can be strung around a room, and an audio signal can be run through it, and then it will couple with your hearing aid and you hear it.
Naturally, they’ve made cochlear implants compatible as well. In concert halls, they will send the mix into the hearing loop. In London, black cabs have tiny microphones embedded in the dashboard, and transmitting hearing loops in the back of the cab. You can go see a performance of Wicked in New York, and the SR guys run a separate mix to the hearing loop, and if you have a cochlear implant with the T-coil mode, the EMF audio signal will go directly into your brain, no old-fashioned vibrating air necessary.
This also means, if you are Deaf, but you play the electric guitar, say, you don’t really need practice amps. You should be able to electrically hook the guitar up to your cochlea. You can buy hearing loops shaped to hang onto your ears like sunglasses, with minijack connectors for your laptop or your iPod.
There are some unsurprising problems: inductance losses roll off high frequencies (just like in any long run of audio-frequency signals through an unbalanced cable), there is limited dynamic range (more specifically, many people with severe hearing loss and the current technological remedies we have for that loss have very limited dynamic range, and so the signal must be kept within that range to avoid unpleasant artifacts). But Richard Einhorn was just on the radio saying it sounded great.
If I understand how this works, any changing electromagnetic field that’s strong enough and within the frequency range of the cochlear implant should come through into your auditory nerves, when T-coil mode is turned on. This is almost like having another sense. People with cochlear implants should be able to “hear” certain EM fields. If you walk past a huge motor, or a prime mover in a power generation facility, you should hear the deep thrum of the field thrown off by the spinning armature. In fact, the pitch would depend on how many arms the armature has, right? In multiples of the rotational frequency. You could tell something about the motor design from the octave of the “sound”.
It is entirely possible that I don’t understand this right, but I just can’t get over the fact that not only do there exist machines that wirelessly transmit audio signals directly into your brain, but that they are already commonplace. They’re in cabs. They’re installed in 18,000 post offices in the UK. The most fundamental thing about the experience of sound, that it is a vibration of air or other medium, that animals developed to sense goings-on in their environment, is now optional. It is now totally possible to electronically hijack the neural circuitry behind this purely for the exchange of cultural information like cab fares and Wizard of Oz musicals and TED talk podcasts, and to skip the whole “vibrating air” thing entirely.