Acoustic mode means: When someone switches off all the irony and self-awareness and just exists in genuine, unguarded sincerity - for better or worse. Acoustic mode is the state of being fully earnest, un-edgy, and. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.