Probably about 20-30% of people at Furnance Fest are Republicans.
The music at Furance Fest is very un-Republican friendly. The -Core scenes and punk bands are vehemently against Trump, so don't expect many MAGAS to show up in attendance.
This is a music festival in Birmingham, AL. If the event draws even 40% from local attendees then plenty of Republicans would be there
It's not, I can assure you that. I doubt there's even 4000 people in the Birmingham area who listen to that style of music much would attend Furnace Fest. Furnace Fest bands on tour at most sell out a like 1200 capacity venue in Minneapolis, there's no way there's an audience of 4000 in Birmingham. Now if you extend "local" to include places like Atlanta and Nashville I could see about 30ish% but those sure aren't conservative cities.
This is the fair assumption of the crowd. Little to no locals are going to be present in the crowd, and those who are, I bet there's a culturally difference with the average voting base of Alabams. Even if you want to say the crows is going to be very white just remember the typical fan of these genres are not the typical white person that votes Republican. Could you picture any sitting Republican listening to New Found Glory? In a more liberal state the attendance would skew even more D, with those that are Republican keeping their beliefs to themselves in order to avoid alienation from the scene.