South Korea redeployed propaganda loudspeakers to the border for the first time in years this week, reportedly blaring weather forecasts, business news and K-pop in response to North Korean trash balloons.

But while the test broadcast immediately drew the ire of the DPRK leader’s sister, it also raised an important question: Can North Koreans actually hear the South’s propaganda clearly on the other side of the 2.5-mile-wide demilitarized zone (DMZ)?

Local media have reportedthat the ROK’s loudspeakers can broadcast as far as 21 miles (34 kilometers) depending on the time of the day — an impressive distance that puts