You don't need headphones to hear the music. Next time you're on the plane, turn up the volume on your armrest and you'll see that the music is playing all of the time. At least that's true on United Airlines where I work as a flight attendant. In between flights, we turn up the volume on a few seats and listen to the music.

I should have been more explicit that the Inflight Power uses technology that allows for other "green" uses, especially harvesting energy from vibrations.

Not as you described it. The device simply converts available electric energy into ... electric energy in a form that works for the iPod. An interesting application? Maybe, altho not many of us fly so much that we'd get something of such marginal utility.

But new, insofar as it converts alternating volatage into steady voltage? No, that technology's a century old, just with somebody else's high volume capacitor and a specialized jolt circuit that waits until it thinks it has enuf for the iPod.

I'll even guess that the parts inside need as much non-green technology as an external battery, which would be much more flexible/useful for almost anybody. So give the inventor his due as having come up with a neat concept. But don't make it "green," a "breakthrough" or showing how to use capture wasted vibratons. None of the above.

I didn't think the headphones were completing a circuit. I've had the impression that the "seat radios" are in fact always on and drawing a load

When you plug-in headphones the magnets start doing work to move the speaker diaphragms to make sound. They draw current to do so. Even different headphones draw considerable different amounts of power, between earbuds and 50mm headphones for example.

An empty jack is not drawing current any more than an empty wall socket is.

-- it seems like sometimes without headphones plugged in, you can just barely hear music escaping from your seat arms.

That's impossible. There are no speakers to create the sound in contemporary seats. You could be referring to seats from decades ago, where "headphones" were actually just hollow tubes that slotted into holes, and the speakers were in the seats, to keep the cost of disposable components down. But I haven't seen those since the 70's.

If the device is just converting the vibrational energy, isn't it truly scavenging from "wasted" energy?

That's not what it's doing though.

Another thing to consider is the energy cost in manufacturing a device, compared with the amount of energy it will harvest over an average lifetime. Circuit boards, soldering, melting metal for parts and wires, manufacturing and assembly, etc all cost energy.

I'm willing to bet that the audio jacks in airplanes don't have a switch built in to only deliver a signal when something is plugged in - it's far more likely that they receive a steady amount of power because that's easier to implement and maintain (no switches = nothing to break at point of connection). Correspondingly, the power used to send the signal is essentially being wasted when the signal isn't being used.-- haggismold

omg. There's an opinion fresh from the ass.

The contributors to "Machinist" and "Broadsheet" and many readers seem equally clueless. But thank goodness for hard sciences.

????

Several readers point out that Inflight Power isn't exactly harvesting "leftover" energy but, rather, finding a use for energy that isn't being offered in a useful form.

Ahhh, still not right.

The energy isn't being used if nobody inserts headphones to listen. Jet fuel is being burned to generate the electricity and exhaust spewed into the atmosphere without any filtering or scrubbing, such as power plants and even your car's catalytic converter do. The device is sure to be rather inefficient at converting the weak and irregular signal back into usable power.

In terms of energy efficiency, cost, and ease of use, a simple rechargeable battery back from Radio Shack is way more useful and versatile.

Where did Salon find Manjoo? The "Machinist" seems to lack even basic H.S. level awareness of how technology works.

Go ahead, use your splitter. Energy comes from jack, gets split, some goes here, some goes there. Just don't split too many times. The more times you split, the more power the little seat jack tries to deliver. Too much and it'll heat up and maybe break (or catch fire if you're unlucky).

Also, don't even pretend you're being green or scavenging energy. Your taking advantage of a power source that the aircraft is supplying to your seat. It's clever, but not environmentally nice in any way.

Yes, you complete a circuit by plugging in an electronic headset. Complete the circuit and you've got both current and a voltage drop, hence power is consumed.

The old style airline sound systems were actually accoustic. The sound was carried through air channels. In that case, yes the same power is used regardless of the headset being plugged in. The headset merely channeled sound that was already produced to you ear. With no headset in place, the sound just kind of sprays the cabin.

However, a simple circuit that uses an audio circuit as a power source is slightly different than one that uses a transducer to convert vibrational energy into electrical energy.

An audio circuit produces an electrical signal that is often passed to a speaker where the electrical energy is converted into accoustic energy. However, a simple filter circuit can convert the electrical signal a DC (direct current) voltage which is what is used to charge batterys etc.

When you see an advertisement for a "200 Watt audio amplifier" it means that the amp can supply 200 watts of electrical energy to a speaker. A simple circuit can use those 200 watts to light a 200 watt light bulb.

A microphone accepts accoustic energy and produces an electrical signal that carries electrical power. Add in a rectifier circuit and maybe you can light an LED or something. Collect the energy for a while (battery, capacitor, super cap, hydrolysis, ...) and you can power something even bigger.

Another kind of "seat radio" is one with a speaker embedded in the seat. Some cars have 'em because they allow a person to listen without having to work so hard to overpower engine/road noise. Turn them off, there should be no sound. Turn them on and you get sound. Turning them on to "scavenge energy" would be extremely wasteful unless the speakers would be turned to that volume anyway.

You are converting energy thusly: DC electric -> audio electric -> audio accoustic -> audio electric -> DC electric. No conversion is perfect and some lose a huge percentage of energy.

Compare that to a wall wart: AC electric -> DC electric (done).

(Note DC -> DC conversion ignored here)