The mini is undetectable over 100ft or so. other drones will interrupt the peace, but this one is far less likely to.

Nah they definitely aren't as bad. People using speakers in public are actively choosing to annoy people when they could have used headphones. There's no headphone equivalent for drones.

Drones are also way way less common than shitty music players.

People who hike with speakers blaring are a strange breed that I’m likely to never understand.

Like, why listen to music in the first place while hiking? I’m out here in the woods to get as far away from civilization as I can. I don’t need $latest_popstar dragging me back.

>Being able to spot a small white object in the sky and hearing it are very different things.

They are but not the way you suggest, you stop hearing it long before you stop seeing it. :)

I do not think that there are ICE versions. But there are many different versions by now, including pump foil (just up-and-down body motion), SUP foil (with paddel), surf foil (wave), wake foil (towed behind boat, but able to let go and just surfing on the boats wave), wing foil (inflatable sail that you hold in your hand, the most popular version) and versions for kite and wind surfers. All are currently significantly cheaper than eFoil (starting around 1k compared to 5k for eFoil) but mostly more challenging, in good sense and bad sense. Some people have said that you learn how to eFoil in 30min. Then the battery is empty. But that is okay as by that time it becomes boring. Which is different to all the other foil sports (exept maybe wake) were most need ~10h to even achive small steps forward. But once you manage, basically every body of water becomes a surf spot.

Wikipedia is actually a pretty good source for this [0]. tl;dr it's not as simple as one drone makes X noise, so 2 drones make 2x noise. For that to happen, the drones need to be making noise at the same frequency and be perfectly in phase. Also, if they were perfectly out of phase, they could cancel the noise from each other out (this is how noise cancelling headphones work).

[0] https://en.wikipedia.org/wiki/Wave_interference

It depends on: the medium, the frequency, the shape of the soundwave, how it is generated (in this case: fast rotating props) the degree to which the frequencies line up (or not) which will result in beats, the phase in case that they do line up, reflections, the distance to the source(s) from the position of the receiver, the air pressure, the direction of the wind and a ton of other factors that result in more or less noise at the receiver.

To say it doesn't behave linearly would be too nice. It's not quite random, but systems quickly become so complex (2 drones: 8 rotors!) that modeling them is non-trivial. Look at the way a steady wind blowing on water can perturb it and how complex the resulting waves are. Sound is similar, you can start off with a 'clean' source (say, an electrostatic speaker) and then you place it in a room and suddenly there are all kinds of places in the room where the sound is louder or where it almost completely disappears. Then you add a second speaker, at a little distance to the first. Put them in parallel to make it simple. Now where you place your speakers relative to each other is almost as important as the distance between the two of them. If you place both speakers so far away that the sound of an individual speaker is below the noise floor of the receiver you can usually manipulate things such that the two signals crest right at the receiver. Alternatively, you can place them so close that either one of them individually is clearly above the noise floor but placing the second one strategically to cancel out the sound of the other (besides those pesky reflections) is a possibility as well.

Sound in free space is complex, and with multiple sound sources and a complex environment it quickly gets up to a level that is probably best described as 'chaotic'.