In the case of urban noise the boundaries are less established. What is the source of noise? How to control it from spilling into other peoples' space? Noise isn't something you can keep to yourself. Here the urban fabric may falter. Recently the New York Times published a series on urban noise. The sources of noise are often far from the "recipients." In a word, hard or impossible to control. There's not much you can do about noise that is generated from a distance. For close neighbors, the only solution may be restraint and consideration. "Neighborliness." Is it too much to ask?
Here in Cambridge we have a dense urban fabric and in some cases, like in the big city, noise is hard to find and control. In other cases it's easy. We live in a small space with two other households immediately in front of us. On all sides there are lots more households. We have a small green space that we maintain as a lush and generous garden, somewhere we can cool off and enjoy the flowers, something everyone can enjoy even though it "belongs" to us.
One neighbor's wall, unfortunately windowless, faces our open space, which we share with the two families in front. The outdated in-wall air conditioners spew their clatter whenever the temperatures warm up. Some days they're roaring at dawn, when it's cool, in the otherwise peaceful moments of the morning. It's a shame, because if we want to catch a breeze outside we also have to catch a few unwanted decibels of mechanical clatter.
Living together in the city is an art and a science. It's an experiment in mutual constraint, an opportunity to develop respect, or at least consideration, for other people who live close by. A bit of a challenge as temperatures approach 100, but maybe worth a try.