The image file that you uploaded .... shown above.
If the 5 V supply is totally removed (ie. switch open), then it looks like the circuit can still be driven by the input signal (ie. "SND").
As long as the source of 'SND' is able to provide the adequate current (power) needed to drive the speakers, then you'll hear something.
If 'SND' is a constant DC voltage ... like 5V, then the voltage divider will drop that voltage. And the capacitor will charge up to that voltage (which takes a finite amount of time). At the same time that the capacitor charges up, the voltage across the speaker reduces (decreases) toward 0V. This puts some energy into the speaker to drive the speaker in one direction. Then, if "SND" becomes 0V, the capacitor can discharge, becoming an energy supplier......and the voltage across the resistor jumps up to the capacitor voltage (and decaying will follow), which drives the speaker in the other direction. If you keep applying 5V and 0V in cycles .... at suitable frequency, then the speaker should make noises....as long as the source of "SND" can supply enough current, and provided that the voltage from "SND" is big enough.
When the capacitor discharges.. the current goes through emitter to base (of the 327).... so need to make sure this transistor can handle the current (for the EB 'diode' current). Similar situation for the 337 (base-emitter current when "SND" is arbitrarily 5V) for the case where the power source (not the SND voltage) is switched out.