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.
Making Changes by Phone. If you cannot find your itinerary online, or you find a flight that is on one of Delta's airline partners, you will need to call a reservation agent to make your change. To make a change to a domestic flight, call Delta at 1-800-221-1212. To make a change to an international flight, call Delta at 1-800-241-4141. Have your ticket number or confirmation number ready when you call. If you do not have that information, the Delta agent can look your information up by name and flight number.