With tickets for all seven of their previously announced acoustic shows already sold out, Foo Fighters [ tickets ] have slipped a couple more shows into their itinerary, and are promising more to come.

Dubbed the "Afoostic" tour, the run--which gets underway July 11 in Seattle--now includes a new stop in Washington, DC, as well as a recently announced second night in Berkeley, CA.

Though band frontman Dave Grohl and company are going unplugged during the upcoming run, they'll keep their hard-rock chops up with an Aug. 18 electric show in Atlantic City.

Tickets for the Washington and Atlantic City shows go on sale Saturday (6/3), while those for the second Berkeley performance are on sale now. More dates will be announced "soon," according to the group's publicist.

In addition to Foo Fighters' regular lineup--Grohl (vocals/guitar), Taylor Hawkins (drums), Nate Mendel (bass) and Chris Shiflett (guitar)--the shows will also feature Petra Haden (violin), Rami Jaffee (keys), Drew Hester (percussion) and former Foo Fighters/Nirvana guitarist Pat Smear.

The set list for the "Afoostic" shows will include cuts from Disc Two of last year's "In Your Honor," which largely houses acoustic tracks, as well as "unique interpretations of favorites from the band's entire catalog," according to a press release.

Pro-surfer-turned-musician Timmy Curran will open the tour's July stops, while Pixies frontman Frank Black will hold down the opening slot for the August shows.

Before setting out on the acoustic trek, Foo Fighters will play a June 17 show at London's Hyde Park. After selling out the original 70,000-ticket allotment, the group obtained the city's permission to expand the concert grounds to accommodate an additional 15,000 fans; those tickets have all sold out, as well, according to the band's publicist.