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Comment by gmueckl | Hacker News Reader

Two big caveats with this tech (from the paper):

- it's really silent. They claim that the signal is audible, but under pretty much ideal conditions.

- creating arbitrary sound with this approach is hard. Each laser sweep generates a sharp wavefront that is audible, but that only eorks ehen the sweep is at the speed of sound. This limits the frequency at which you can emit those pulses and their shape is fixed, too. The only really changeable property is amplitude.

Not sure if this can be turned into a reasonably high quality source.

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They mention 2 methods in the article, the sweep method, and plain old modulation. If the 2 methods could be combined it might work better.

The sweep could be sped up by several orders of magnitude, and the modulation could be coordinated with it to create traveling pulse trains toward the listener that would have higher fidelity.

The sweep is fixed to the speed of sound or else the whole trick behind it falls apart. The paper describes that in length.

Yes, but the point of sweeping seems to be to add energy to a traveling wave front. You can still amplify the wave by sweeping faster and bumping the power at the appropriate time, but you would gain fidelity because you're not limited to single square waves.

No, the amplification can only work at the speed of sound, neither faster nor slower. The paper analyzes how the wffect falls apart when you deviate from c.

What you possibly could do is to have multiple laser beams forming a sweeping comb pattern. Depending on dispersiom and other effects, you might be able to do some waveform shaping. But that is very elaborate for a loudspeaker.

That's like saying audio over radio waves can only be sent with spark gaps... you simulate this "sweeping comb" with a fast sweeping, and even faster modulating laser.

It states 60db - that’s normal conversation volume. Does the paper say otherwise?

I could not find a reference to 60dB in the paper. It states 30dB SPL in the relevant plot, which is very quiet.

"In the lab, the researchers showed that commercially available equipment could transmit sound to a person more than 2.5 meters away at 60 decibels using the laser sweeping technique"

Granted, the laser sweeping technique trades off fidelity for the volume, this is still just laboratory tests and is not a "final product" in any sense.

This claim still isn't in the paper, though. Not sure why the press release makes this much bolder claim. Seems a but weird to me. If I had the measurements to prove that, I'd include them in the paper.

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