not the AD8397
There is nothing in the datasheet that would suggest that it can swing below its negative rail.
I don't believe anyone did say the AD8397 can swing below its negative rail. There are a other ways of driving headphones from an op-amp such as the AD8397 without using AC coupling capacitors but that wasn't the original topic of this thread.
It doesn't need to swing negative to work ... It Doesn't Need To Swing Negative to Work! ... IT effin' DOESN'T NEED to effin' SWING effin' NEGATIVE to effin' WORK!!!!
Duhhhhhhhhhh!!!
Dave went over this in his opamp video,EEVblog #600 - OpAmps Tutorial - What is an Operational Amplifier? (around 28:00):
You are quite correct, the output of the amplifier itself does not need to swing negative, but the signal applied to the speaker absolutely must swing negative; the net DC component applied to the speaker needs to be kept to very small values, preferably zero. It is the job of your "emergency"
caps to remove the DC bias from a conventional power amp run from a single supply rail.
I appreciate you are finding this entire topic very difficult to understand, but the capacitor effectively converts a 0 to Vcc swing to a -Vcc/2 to +Vcc/2 swing.