Since all else isn’t equal, you could design cities that are quieter than the most suburbs. But you could also design suburbs that are quieter than most cities.
In the US at least I linked a study that showed cities are far louder on average.
You cannot have significantly more people/square meter with everything else remaining equal. Cities are like stars - quantitative change in density causes qualitative change in behavior.
Since all else isn’t equal, you could design cities that are quieter than the most suburbs. But you could also design suburbs that are quieter than most cities.
In the US at least I linked a study that showed cities are far louder on average.