Noise reduction from neighboring properties - ideas?

Low tones do not carry as far as high tones [...]

This is not correct. Low frequencies are attenuated less in air than high frequencies.

[...] and the sound waves tend to stop relatively easily at obstacles. Roughly speaking, where you cannot look, significantly less will reach you than at the place of generation. But where air can pass through, sound will also pass through. If you want to block low tones in this case, you need mass, i.e. a wall. Heavy and man-height.

However, this is (partly) correct. Low frequencies do not bend around obstacles as easily as high frequencies. However, as a very rough rule of thumb, the obstacle must be at least as large as the wavelength to count as an obstacle (at 100Hz this is a little over 3m). And especially bass tends to simply travel directly through the obstacle, so (direct) airborne sound is not even the problem.

Ultimately, it doesn't matter. The question was how to counter "normal" volumes from next door if you have a problem with them. Right? No matter how considerate you are, the humming of the lawnmower robot and the pump of the whirlpool can also be heard next door.

Laugh... thanks, Stefan! You can see where the knowledge of noise generation from spinning washing machines and whirlpool pumps reaches its limits. At high and low frequencies, the answer was not only related to the behavior of sound waves but also to how a person perceives them. I phrased it too simply. Thanks for clarifying! Best regards Gabriele

Sorry, before I would do such nonsense, I would rather first try a conversation.

I already advised that, as did several others before me, and regard the "nonsense" only as plan B (because for some people plan A works (only / significantly better) and for others plan B accordingly works. That a conversation is successful requires the recipient to have a brain between their ears (which unfortunately no longer seems to be the standard nowadays).

when I am annoyed by noises in our current rental apartment, I sometimes put on my noise-cancelling headphones,

I don’t think they come in child sizes ;-) however, you can at least narrow down whether you are "hearing" sound or vibration with them.

For us, it is such that some newcomers take legal action against church bells/cowbells/old lady smell etc.

If that’s not an argument in favor of the locals model ;-)

For me, it’s a certain neighbor, with whom there was already some stress over other things (and whose hobby, to my horror, is various petrol garden equipment...).

Some idiot is always mowing somewhere [Reinhard Mey]

Is it possible to set up a radio so that the bass "flows/radiates" in a desired direction, i.e. towards his house and not towards the house of the thread starter?

Because of their spherical distribution, the bass would not do that, but the portion of the higher tones that also radiate towards the OP could be significantly reduced – with the consequence that she might concentrate even more on the droning :-(

I’m glad to have built with consideration for aircraft noise and not just U-values.
The result is that the house is soundproof, and the best part is,
today at 3 PM Berlin-Tegel was closed, no more planes.
Anyone building in a new development area should pay more attention to soundproofing; that’s a longer-lasting annoyance than the last ten heating cost reductions.

What exact measures did you take there?

Solid Poroton filled, 42cm, 3-layer glazing with RC2 and 45dB, no roof windows, a lot of insulation in the roof with double 15mm plasterboard. These were effective measures for us in terms of price/performance.