[t-3]

It's illegal in a few places in the US, but not everywhere. It's definitely not illegal to put in a few kW of amplifiers and a few square feet of speakers, and often not even a problem to turn them all the way up and stop whole areas from hearing anything.

[mc32]

Those loudspeakers on wheels at volume are illegal in many places -what’s not happening is police caring enough to make arrests. Maybe other jurisdictions will take a cue from Las Vegas and begin enforcing laws to protect normal people from teenagers and adult idiots who still think they’re teenagers taking over streets.

[rlpb]

Arrests seem like overkill. Ask them to stop, issue a fine, whatever. Sure I get you're asking for any enforcement at all. But hyperbole has a polarizing effect on discourse we should try to avoid, IMHO.

[bloak]

Yes, I agree, but really we shouldn't even be comparing "arrests" and "fine". The latter is a punishment, and the former is a practical measure to prevent a future crime (such as destruction of evidence) or to prevent someone from evading justice (by destroying evidence, hiding or leaving the country, for example). Obviously some police forces do use arrests and searches and confiscation of "evidence" as a form of extrajudicial punishment but that shouldn't be allowed.

[ChoGGi]

Arrest? No, but if you've done illegal modifications to your ride then being forced to get it from the impound lot seems fairer to me compared to a ticket you can pay at your convenience.

[ssl-3]

In this case, it's not the modification that is potentially illegal, but instead the noise that it can make.

A big-honking stereo system isn't illegal to have at home or in a car in any jurisdiction I'm aware of, but there can be limits on how loudly it is used.

A stereo is a lot like a hammer in this way: Anyone can have a hammer. There's plenty of legal things a person can use a hammer for, and also plenty of illegal things as well. But the hammer itself, of any size, is A-OK.

There can even be time limits on when hammering is allowed[1].

[1]: I was involved in fire remediation after a friend's house burned. There was a lot of work to do, and we were working very late. The police showed up and politely told us that we'd need to keep it quiet until morning and suggested that they would find some way to make us quiet down if we didn't. We stopped hammering and tossing things into the dumpster at 11PM after that incident.