Weight: 2 lb.
Estimated Value (Sane Cost Guide): 450 gp
DMG Value: 501 gp - 5,000 gp
You can use an action to speak the horn's command word and then blow the horn, which emits a thunderous blast in a 30-foot cone that is audible 600 feet away. Each creature in the cone must make a DC 15 Constitution saving throw. On a failed save, a creature takes 5d6 thunder damage and is deafened for 1 minute. On a successful save, a creature takes half as much damage and isn't deafened. Creatures and objects made of glass or crystal have disadvantage on the saving throw and take 10d6 thunder damage instead of 5d6.
Each use of the horn's magic has a 20 percent chance of causing the horn to explode. The explosion deals 10d6 fire damage to the blower and destroys the horn.
Source: DMG p174