When iconic radio station WBCN (104.1 FM) flips formats Aug. 13 it will mark the first time since Lyndon Johnson's presidency that the station will be missing from the Boston rock radio landscape.

For more than 40 years WBCN helped define local tastes and influence the national music scene. But its ratings severely declined in recent years and parent company CBS Radio is now shifting the station's focus from modern rock to adult top 40 and making room on the dial for a new all-sports station.

"I'm sure that it's going to shock a lot of listeners because there are generations who've listened to that station," says Mike Boyle, former senior editor of Radio & Records.

CBS' adult top 40 Mix 98.5 will move its programming to WBCN's 104.1, and 98.5 will become "The Sports Hub," a new CBS offering dedicated to full-time sports coverage. WBCN will remain as a Web- and HD-cast after the change.

"’BCN was a lifestyle radio station. It was a fabric of the community," says Oedipus, WBCN's former longtime PD who helmed the station through its most successful years. "My goal was always to make it as important to Boston as the Red Sox were or the Boston Globe, and 'BCN was that."

'BCN is credited with being the first station in the country to play U2 and helped to break homegrown acts like 'Til Tuesday and the Cars nationally. In the 90s, record label and radio executives considered the station to be a national tastemaker that could influence song additions to other station playlists.

"We broke so much new music," Oedipus says. "From U2 to the Clash to Talking Heads to the Ramones to Pearl Jam to Coldplay. Many of these artists got their first spins on WBCN."

Oedipus' 27-year career at WBCN began in 1977 as a DJ and he then helmed the station as PD from 1981 until he exited in 2004. He became VP of alternative programming for Infinity Broadcasting, WBCN's parent company, which later became CBS Radio.

The station's swagger took a hit in recent years as its national influence and local popularity waned and ratings suffered as rivals WAAF (107.3) and WFNX (101.7) gained in market share. "I think it would be fair to say that they ran a little bit tighter of a playlist in recent years and weren't quite as adventurous," Boyle says of WBCN.

"The sad part is, after Mel Karmazin left [Infinity Broadcasting], WBCN was dreadfully mismanaged and they basically ruined the company and WBCN specifically,” said Oedipus. "They eliminated, layed off or fired the creative people and they programmed the station with focus groups and research and not with gut."

Boston may be the most competitive rock market in the country, according to former Radio & Records executive editor Paul Heine, with WBCN, WFNX and WAAF, among other stations, all directly competing. Additionally, signals from smaller, neighboring markets like Providence, R.I., and Manchester, N.H., are easily picked up in Boston.

WBCN's demise marks the third time this year that a prominent rock station in a major market has ceased operations, after New York's WXRK ( K-Rock 92.3 FM) shuttered in March and Los Angeles' Indie 103 (103.1), a 5-year-old station that found a strong niche following, shut down in January.

But this isn't a trend, according to Ron Valeri, PD of WAAF in Worcester, Mass. "Rock radio is doing fine. Formats are not the problem. Deficiency of execution of a format is the problem," he says.

CBS' move to launch a new sports station isn't surprising, Heine says. "Sports on FM is growing and CBS has been aggressive about switching things up when something isn't working." And the growth of sports programming on FM has coincided with Boston's incredible run of professional sports championships this decade. Three of the city's major sports franchises - the New England Patriots, the Boston Red Sox and the Boston Celtics - won a combined six championships since 2002.

"As an operator in Boston you have that added advantage of being in 'Title Town,' " Valeri says when asked if there was room on the dial for a new sports station. "So I think there's plenty of room for great content. There could be room for 10 [sports stations] for all we know."

Sports aside, as expected, WBCN's fans aren't happy. WBCN commenter Ethyl Alcohol hit the message boards with a simple message that seemed to sum up the mood: "CBS, you suck."

"Do we really need another sports station in Boston?" commenter Jaked asked. "I understand it all has to do with money, but this is a Boston landmark in radio."

[Disclosure, Chris M. Walsh began his career as an intern at WBCN.]