If you front what is arguably the most respected progressive death-metal band working today, how do you keep your hard-core fan base stimulated? Opeth’s Mikael Akerfeldt answered that question by eliminating the death-metal element from the virtuosic Swedish quintet’s 10th studio album, Heritage, released in mid-September.

Examining Heritage’s surreal cover art, you’d probably assume doomy shredding and sickeningly fast bass rolls await within. However, this is the first Opeth record since 2003’s soft and mournful Damnation to lack the 37-year-old singer-guitarist’s gargantuan death growls.

“The songs just didn’t call out for that,” says Akerfeldt, calling from a tour stop in Nashville, Tennessee. “I think it would be bad taste to include one of our famous past elements just because people expect it. I always follow the vibe of the songs.”

Exuding a retro aura, this eminently listenable 10-track outing offers something for fans of many genres. Akerfeldt’s melodic vocals range from a full-throated cry to a gentle falsetto, either of which could have graced the ’70s prog heyday of ELP and Gentle Giant. From the sensual guitar figures recalling Chris Isaak’s “Wicked Game” in “Nepenthe” to Martin Mendez’s slinky bass work on “The Lines in My Hand”, there’s always a captivating left turn coming up into jazz, blues, or classic rock. And despite the familiar lyrical focus on loss, alienation, and dead gods, Heritage is pretty happy by Opeth’s standards.

That happiness may stem from Akerfeldt’s recent close encounter with the one Swedish group that everybody knows. In the CD booklet’s acknowledgments, the name of ABBA’s Agnetha Fältskog stands out.

“We recorded Heritage at the former Metronome Studio, where ABBA did their pre-1978 albums,” explains Akerfeldt. “The studio owners knew I was a big ABBA fan. One day they said, ‘We love you guys. Come have dinner with us at the end of recording.’ We agreed. And we went up to the place, and the engineer’s wife said, ‘Oh, I invited a friend you might recognize.’ It was Agnetha. I was like, ‘I can’t believe it.’ My heart started beating. We spent the evening with her, and I even danced with her. The jukebox went on with some ’60s rock, and I’m dancing with the Dancing Queen. One of the best nights of my life.”

While his dream collaboration with the ultra-private blond songstress and ex–Deep Purple riff master Ritchie Blackmore may never come about, Akerfeldt can always bask in the uncritical admiration of his two daughters, seven-year-old Melinda and three-year-old Mirjam. “They like our music, but they don’t see a difference between the most brutal Opeth song and the latest Justin Bieber single,” he says with a chuckle. “It’s all just stuff they can dance along to.”

Opeth plays the Commodore Ballroom on Thursday (October 13).