“when Jabin king of Hazor heard.” The emphasis on the sentence is on “heard.” Many people in the Book of Joshua “heard,” and how they respond when they hear reveals their heart (cp. Rahab (Josh. 2:10); kings of the Amorites (Josh. 5:1; 9:1); the Gibeonites (Josh. 9:3); Jabin (Josh. 11:1)). Also, when people hear, what do they do? The Gibeonites “sent” to Joshua a delegation to seek peace, while others, such as Jabin here, “sent” to form an army and fight.
“Jabin.” A dynastic name held by more than one king. “Jabin” was not a title, but a name held by more than one person in the dynasty. This is similar to “Herod” in the New Testament (“Herod the Great;” “Herod Antipas;” “Herod Agrippa I,” Acts 12, “Herod Agrippa II, Acts 25; etc.). This Jabin is different from the one in Judges 4 and 5.
“Hazor.” The largest Canaanite tel in Israel; over 200 acres. That is much bigger than Jerusalem up until at least the Roman period, certainly bigger than Jerusalem in the Old Testament.
“Jobab king of Madon.” Besides Jabin, Jobab is the only other king in the northern coalition who is named. Perhaps this indicates he was better known for some reason.