Well, my speaker system (JBL SCS180.6) is not the newest but works fine. During use, the 150W subwoofer typically uses about 15W unless I really crank up the volume. There is a selection switch in the back for “On” or “Auto”. On “auto” it will go to standby if no signal is received and turn on automatically if needed (the current state is indicated by an LED (green=On, red=standby).
What surprised me was that while in standby that thing still uses about 9W of power! (as reported via tp-link HS300). Seems high but apparently normal for these kinds of devices. (I am tempted to put it on a switched outlet, triggered when the receiver is turned on but probably not worth the effort). I wonder if more recent subwoofers have a more pronounced standby advantage.