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.
If you booked your ticket on American Eagle/American Airlines you have several alternatives to traditional check-in. Select the one that suits you. Flight Check-In on AA.com - Flight Check-In can be found on the AA.com home page, or under the 'Reservation' tab. Flight Check-In is available if your flight is less than 24 hours but more than one hour from departure. Login to AA.com or enter the passenger name and record locator, print your pass and you're ready to go. Round Trip Flight Check-In is also available. Check in and print your boarding passes for both your outbound and return flights at the same time (as long as your return flight is within 24 hours of initial check-in). For more information on Flight