The strong turnout for 3D showings of Disney-Marvel’s “The Avengers” helped average domestic ticket prices hit a record $8.12 during the second quarter. That’s up from the previous high of $8.06 set this time last year.The National Assn. of Theater Owners released the quarterly stats on Friday. Average ducat costs rose 2.5% this past quarter over the first quarter, which saw a 1.1% increase over fourth-quarter 2011. It’s not unusual for the average domestic ticket price to go up during the second quarter, based on increased demand and higher 3D prices. This year, “Avengers” smashed domestic opening records, scoring a massive $207 million Stateside bow; more than half of that came from higher-priced 3D screens. The stereo format has been waning, however. “The Amazing Spider-Man” and “Prometheus” generated about 40% of their B.O. from 3D tickets, excluding Imax. Summer box office, at $3.404 billion, currently trails last year’s record-setting season by 3%.