>Those are part of those sh*t-eating quiet zones.

It's what's called an AHS, "automated horn system", and it's no so much "quiet" as highly directional -- aimed at the traffic which needs to hear it and aimed away from the surrounding neighborhoods which don't want to hear it.

>The object at the top indicates if the engineer has to give the ol' "long-long-short-long" for the crossing or not,

Misleading. If that top indicator isn't illuminated he does, but otherwise no whistle blowing. However, as the case with "quiet zones" there are situations where the E has to sound the horn regardless of whether or not the indicator is lit (and the AHS is sounding).

> while the lower object is a speaker that plays a simulated train horn

Correct.