O.C. POP MUSIC REVIEW : Duo Covers More Than the Bass-ics : Rob Wasserman’s aggressive playing is at center of an intense show with Dead member Bob Weir in which they explore a variety of sounds and moods.

Bob Weir’s concerts with bass virtuoso Rob Wasserman started in 1988 as an impromptu vacation from Weir’s regular gig with the Grateful Dead. By now, the Weir/Wasserman pairing, which made its fourth Orange County appearance Thursday night at the Coach House, has formalized into a relationship more akin to a time-share.

Weir and Wasserman will release an album in September. And Thursday night, folks in the audience were even calling out requests for songs the duo has performed in previous concerts.

The pair may have lost the elements of surprise and spontaneity usually generated when a member of a well-known band takes a solo flier, but their intense one-hour, 35-minute set demonstrated that the association is worth a fourth listen. Much as Japanese poets seem to express an endless diversity of ideas and emotions within the strict limitations and minimalist format of the haiku, Weir and Wasserman used the bass, (mostly) acoustic rhythm guitar and Weir’s limited singing voice to explore a variety of sounds and moods.

With Wasserman’s aggressive bass playing as the centerpiece of the show, the two delved into a wide variety of material that included blues classics (“Walking Blues,” “Spoonful”), pop standards (“Fever,” “Twilight Time”), soul numbers (“Take Me to the River”), Grateful Dead songs (“Victim or the Crime”) and particularly Weir’s solo material (“Josephine,” “Shade of Grey,” “I Want to Fly Away,” “Heaven Help the Fool”). Wasserman, who with his albums “Solo,” “Duets” and the upcoming “Trios” has launched a campaign to make the bass a lead instrument, was the driving force on most of the numbers. Using a futuristic six-string Clevinger electric upright on most songs, Wasserman attacked his instrument the way an inquisitor works on a prisoner. Alternately plucking and pounding the strings and sometimes sawing at them with a bow, Wasserman persuaded his bass to respond with a nervous, edgy intensity.

Weir’s elegant rhythm guitar provided a welcome release from the tension, but his rather dimensionless singing did little to expand on the textures of the bass and guitar. The crowd, however, applauded wildly every time he broke into a falsetto croon.

Wasserman eased off from his harsh, booming electric bass attack when he picked up an acoustic upright bass for an interlude of pop standards early in the set. During that four-song segment, which was highlighted by a seamless segue from “Eternity” into “Fever,” Wasserman contented himself with jazzy solos.

Toward the end of the evening, after another solo segment by Wasserman, Weir took a more assertive role on his guitar, switching his acoustic instrument for an electric and playing lead on “Victim or the Crime” and “Josephine.”

For their two-song encore, Weir and Wasserman were joined by opening act Susan James. James’ sweet harmonies with Weir on the chorus to “Spoonful” added an additional dimension to the stark Weir/Wasserman sound.

In her 45-minute opening set, James showed that she is already a master at exploring the emotional and sonic possibilities of the minimalist format of voice and acoustic guitar. James used the impressive range of her trained voice as well as the knowledge of ethnic music she acquired as an ethnomusicology major at UCLA to create an entire world of innovative sounds and moods. She drew an ovation from the crowd for her impressionistic instrumental depiction of a New Mexico thunderstorm.

James’ long blond hair and folk-based songs have caused her to be compared to Joni Mitchell. The inventiveness of her eight-song set, however, showed that James is perhaps most like Mitchell because she is like no one else.