There is a broad range of equipment falling under this label, from small portable units to very large pieces of equipment occupying half of the basement or the roof in a building.
According to their size and their use, they will have to comply with occupational noise regulations, environmental regulations, community noise control regulations, etc.
Noise control of such equipment can be carried out using the relevant soundproof enclosures and silencers. Usually the manufacturer of such equipment has such items in his catalog.
Now this is a modern life ubiquitous piece of equipment. Unfortunately, the lawmakers who devised dwelling acoustic regulations did not necessarily think of it when stating recent regulations! More to the point, the frequency range and power output have steadily grown over the years, and this is bound to create problems.
There are a few regulations applicable on the subject: community noise control of course, and even occupational noise regulations pertaining to noise exposure. Some countries have issued specific regulations regarding public receiving spaces where amplified music is played. Such regulations usually feature a minimum sound insulation requirement to protect the neighborhood; in addition, they usually define a maximum sound level in the public accessible areas.
When it comes to a simple sound system operated by an individual community, noise regulations apply. In addition, in a multidwelling building there may be some additional requirements in the internal contractual rules in force.