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.
KLM Airlines web check in is the fastest and simplest way of checking in. With KLM Airlines online check in, you can check-in from 30 hours until 1 hour before flight departure. For domestic flights, passenger must be checked in at least 40 minutes before scheduled departure. For international flights, passenger must be checked in at least 60 minutes before scheduled departure.