Orchestra of St. Luke's at Carnegie Hall For the Hungarian conductor Ivan Fischer the unexpected is the norm. Among other experiments, Mr. Fischer likes to test unusual seating plans with the Budapest Festival Orchestra, which he helped to found and directs, and other orchestras, to alter balances and bring out intriguing details, especially those involving woodwinds. Orchestra of St. Luke's Ivan Fischer conducting a program including Mozart's Requiem and Symphony No. 34 at Carnegie Hall on Thursday. So it was something of a surprise, when he conducted the Orchestra of St. Luke's in Mozart's Symphony No. 34 in C at Carnegie Hall on Thursday evening, that the seating was mostly conventional. The only real eccentricity I could make out from my vantage point was a forward placement of one bassoonist. But Mr. Fischer made up for that in the second half of the program, consisting of Mozart's Requiem. Here many of the female members of the chorus, Musica Sacra, were strewn among the orchestra, and the vocal soloists took places surrounded by choristers. The purpose seemed not so much to rebalance the sound directly as to involve all the performers in one another's business. In particular, Mr. Fischer had explained in a note to the orchestra, he wanted to involve everyone in the work's texts. "My main purpose," he wrote, "is that instead of mechanical instructions, like play this note long and the other one short, instrumentalists should also experience the text, playing, and in a creative and organized way, declaiming with the singers." Players in Mozart's day, he noted, would have been familiar with the words; not necessarily so today. But there was also a significant rebalancing within the orchestra. The two basset horns (essentially lowish clarinets) and two bassoons, the only woodwinds in the work, were placed front and center, right before Mr. Fischer, giving the basset horns, especially, enhanced prominence. Since Mr. Fischer reliably draws the best - meticulously prepared and deeply committed performances - from any orchestra he conducts, his experiments must generally be accounted successes, certainly not mere gimmicks, though it is not always clear how much credit to accord any particular tweak. You could argue for a little less basset horn here, but you could only admire the unified choral and orchestral sound. And the feel of the performance over all (like that of the symphony) was one of passionate involvement with no sacrifice of technical refinement. Of the vocal soloists the soprano, Dominique Labelle, was splendid, and the tenor, Joseph Kaiser, countered her well. The mezzo-soprano, Kelley O'Connor, was adequate to her smaller task, but the baritone, Richard Paul Fink, was a little slow to grasp his pitches firmly.