R&B/pop superstar Usher nets his fourth No. 1 album on the Billboard 200 as "Looking 4 Myself" debuts atop the list with 128,000 copies sold, according to Nielsen SoundScan.

That's off quite a bit from the start of his last full-length studio set, 2010's "Raymond v Raymond." It bowed at No. 1 with 329,000. (Since then, he issued the "Versus EP" in 2011, moving 46,000 in its debut.)

Rather surprisingly, "Looking 4 Myself" also registers Usher's smallest first-week sales for a regular studio album since 1997's "My Way" bowed with 67,000.

It's surprising because the sales for "Looking 4 Myself" are considered to be unusually low. How can an act have a 61% drop in first-week sales between studio albums-and in only two years' time?

One theory: Since 2010, Usher has been pursuing a pop/dance audience, while alienating his core R&B fans.

After introducing "Raymond v Raymond" with a series of R&B-focused hit singles like "Papers" and "Hey Daddy (Daddy's Home)," Usher dropped the full-throttle pop/dance track "OMG." The Will.i.am-produced tune became a No. 2 hit on both on the Mainstream Top 40 and Mainstream R&B/Hip-Hop airplay charts. He then followed that up with other dance tracks like the Pitbull-assisted "DJ Got Us Fallin' in Love" and the RedOne- produced "More." While each reached the top 10 on the Top 40 tally, neither dented the R&B/Hip-Hop list.

Since then, Usher's career on the charts has become increasingly segmented, with certain singles earmarked for top 40 radio and others promoted only to R&B outlets.

"Looking 4 Myself" was led by the single "Climax," which is spending its 10th straight week at No. 1 on the Hot R&B/Hip-Hop Songs chart. The track, which came out in late February, also reigned atop the Mainstream R&B/Hip-Hop airplay tally for four weeks.

Yet, on the Mainstream Top 40 chart, "Climax" spent a scant three weeks on the list, topping out at No. 36. Conversely, it wasn't until late April when the album's second single was released: the top 40-focused "Scream." This week it returns to its to-date peak of No. 10 (up one slot) on Mainstream Top 40. Where is it on the R&B/Hip-Hop airplay list? It's not. (You get the idea here, right?)

Have Usher's core base of R&B fans become turned off-or simply confused-by his dance leanings? It's not like he hasn't dabbled in the pop/dance arena before ("Yeah!" anyone?), but those were across-the-board smashes. They weren't designed for one format over another.

Also, the top 40 market is driven by hit singles and song downloads, not full-album sales. Even for a star like Usher, if you're courting that audience, you run the risk of losing album sales in lieu of mega-selling singles.

sheeran sizzles: British singer/songwriter Ed Sheeran takes a bow at No. 5 on the Billboard 200 with his first full-length album, "+." The set starts with 42,000 and also debuts at No. 1 on the Folk Albums chart. Of its first-week sales, 79% were digital downloads. That's not too surprising, as Sheeran got a lot of love from the iTunes store last week. The retailer offered the album's "The A Team" as its free single of the week and promoted it on the store's front page.

The album has been a smash in Sheeran's homeland, where it debuted at No. 1 in late 2011 on the U.K. albums chart and currently sits at No. 7 in its 40th week on the list.

Sheeran's arrival is the highest debut for a U.K. solo artist's first full-length album since Susan Boyle's "I Dreamed a Dream" bowed at No. 1 on Dec, 12, 2009. The last U.K. male to bow higher with his first full-length was Thom Yorke (of Radiohead) on July 29, 2006, when "The Eraser" debuted at No. 2. "+" follows Sheeran's "The A Team EP," which reached No. 14 on the Heatseekers Albums chart last month. Earlier this year, Sheeran won two BRIT Awards for British breakthrough act and British solo male artist.

'Believe' it: Justin Bieber's just-released "Believe" has all but locked up a No. 1 debut on the Billboard 200 next week. Industry sources suggest the album will sell in the range of 410,000-440,000. It's poised to earn the highest debut sales frame of the year and become Bieber's best ever. It will surpass 2012's current debut champ, Madonna's "MDNA," which started with 359,000. Bieber's best sales week thus far was when "My World 2.0" sold 291,000 in its second week in April 2010.

Other albums aiming for high entries next week include Kenny Chesney's "Welcome to the Fishbowl" (200,000 or so), Fiona Apple's "The Idler Wheel" . . . (around 70,000) and the Smashing Pumpkins' "Oceania" (50,000-ish).