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Ask HN: sound - electricity?

9 points by jibiki ↗ HN
I was thinking about doing a little wind power project, and thought it would be cool to not use a turbine... so, what's a cheap and easy way to generate electric power from sound? (Maybe using those little piezoelectric buzzers?)

6 comments

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ars
Wind essentially IS sound - but with a very low frequency.

Sound is air moving, wind is air moving.

You can use a turbine that spins forward and back I suppose. You'll have a hard time with this - you'll need to match your turbine to the frequency of the sound. Using a microphone works, but only for frequencies in human range.

If you want to catch more energy you'll need to handle infra-sound. Meaning a massive microphone.

J_McQuade
When it comes to power from sound, be warned that results are likely to be rather disappointing - there's a reason microphones and guitar pickups benefit from such highly sensitive pre-amps! If you're just looking to do it out of intellectual curiosity, though, then piezos will at least get you somewhere - like DC motors, they're a 'two-way' thing; put power in, get vibration (sound), put in vibration, get (a little) power. You can often scrounge them from old toys, too, so they might be worth a look.

Other than that, there are a few interesting projects out there looking at alternatives to turbines for generating wind energy - my favourite would have to be this one:

http://www.popularmechanics.com/technology/industry/4224763....

Cobbling one of those things together could make for an interesting and fairly cheap project - if you find the time to do it then I'd love to see the 'vital statistics' of how much juice it'll give you!

jibiki
Thanks, that looks awesome. It's hard to find any good guides online (wikipedia links to one that makes no sense at all) but it seems like an easy project to do without instructions, since all it takes is a couple solenoids and a magnet or two.

Just experimenting with paper strips, it seems like the frequency depends on the width between the membrane and the base. Does anyone know if/why this is true?

electromagnetic
I'd say, depending on your scale, the best power generation you're going to get out of sound would be to use a very large and light membrane to catch the sound and tie it to piezoelectric cells.

You want to produce the maximum deflection possible on the piezoelectric cells as this will produce the largest amount of electrical energy. This will probably be cheaper to do by connecting something like a mylar sheet (a cheap place to look would be the foil wrapping-paper at the dollar store) to some piezoelectric cells.

I'm unsure if piezoelectric cells alone would receive enough force to produce a noticeable effect.

An alternative would be to produce a very large cone and place a piezoelectric cell in the tip of the cone. This would perhaps be a lot less work. However I have a greater understanding of electrics than acoustics, so I'm unsure if it would be better to channel the sound to a small surface or to simply use a large lightweight membrane.

Hopefully this helps you some.

drhowarddrfine
I had not thought of this and I congratulate you on being so clever to think this up. I don't know if it would work but it's well worth considering.