The behavior of a sound wave is affected by the density of the medium, the temperature of the medium and the pressure of the medium if it is a gas. Motion of the medium independent of the sound wave may also affect the way sound propagates.
Yes, you may check-in for your Delta Air Lines (DL) flight with your mobile device starting 24 hours and ending 60 minutes before the scheduled departure time (depending on your departure city and destination) to receive a mobile boarding pass on your mobile device.
: Yes, you may check bags but you must drop them at the airport baggage drop before the check-in deadline for your flight. Can I pay bag fees with the Delta Air Lines (DL) online web check-in?: Yes