When he finished composing his Symphony No. 6, Gustav Mahler had a percussion instrument specially built for use in the finale. He envisioned it being hit with a large hammer to achieve what he described as a “short, powerful, heavy-sounding blow of non-metallic quality, like the stroke of an ax.”

An opportunity to try out the contraption arrived several weeks before the symphony's 1906 premiere, when Mahler conducted a private read-through of the score. Mahler asked a percussionist for a demonstration. The orchestra fell silent waiting for the mallet to fall. Just a dull thud. Mahler insisted on a repeat. Same result.

The composer then “angrily rushed over and struck the instrument with all his force,” Mahler biographer Henry-Louis de la Grange writes. “The inadequacy of the result compared with the effort required to produce it provoked general hilarity among the musicians.”

That may have been the only time anyone ever laughed about anything having to do with Mahler's Symphony No. 6.

This week, the Baltimore Symphony Orchestra and music director Marin Alsop will tackle this daunting work, known, for good reason, by the nickname “Tragic.” The extra-percussive punctuation that occurs in the last movement suggests blows of fate that can bring down even the most heroic of humans.

If all goes well, those crucial blows will hit the spot in the BSO performances, thanks to an instrument crafted by one of the orchestra's percussionists, John Locke, who also made the hammer that his colleague Brian Prechtl will wield.

“There's no standard instrument to use,” says Locke. “The usual tactic is to get a box and a sledgehammer. That's OK. But I wanted to make this a musical instrument, not something that sounds like an accident. My goal was to get something truly exceptional. I just have this sound in my mind.”

So did Mahler. He never did realize his ideal for the hammer blows the few times he got to conduct the Sixth before his death at the age of 50 in 1911.

This is one of Mahler's most personal and absorbing works, and the only one to end without some sense of hope or at least a path toward peaceful resignation. That it meant a great deal to its creator may be gleaned from the description of him backstage after the dress rehearsal before the premiere in 1906 in Essen, Germany.

“Mahler walked up and down the artist's room, sobbing, wringing his hands, unable to control himself,” according to his wife, Alma.

Critics who attended the premiere and subsequent performances in Berlin and Vienna couldn't control themselves, either. Reviews were brutal: “crazy cacophony,” “physical torture,” “satanic symphony.” Audience response was divided.

Although beauty and warmth can certainly be found in the symphony — the ecstatic, lyrical theme that breaks through the darkness of the first movement (Mahler told Alma that he tried to sum her up with that melody), the poetic, poignant Andante — the prevailing color is dark.

The Sixth opens with a grim march that soon leads to a simple, but indelible, device — an A major chord that changes to A minor. That harmonic shift will haunt the rest of the 75-minute work, especially the long finale, when it seems as if the symphony's protagonist is about to triumph, only to be stopped in his tracks. This is where those hammer blows come in, occurring at key points along the way.

“They are so effective, so monumental,” Alsop says. “It's a shocking sound. There is a devastation about it.”

Mahler originally intended for there to be three blows, but later eliminated the third. For most listeners, two are plenty.

Alma Mahler maintained that her husband had inadvertently predicted his own fate when he composed the Sixth. He faced three crises a year after the piece premiered — his resignation as head of the Vienna Opera after relentless resistance from various, especially anti-Semitic, factions; the death of his oldest daughter at the age of 4; and the diagnosis of his heart disease a few days after her funeral.

Taking out the third hammer stroke may have been Mahler's superstitious way of trying to keep that diagnosis from being fatally fulfilled. Alsop suggests another reason. “I think he considered the third blow to be too depressing, too dark a look at life,” she says.

Not that the symphony is made sunnier by only two strokes.

“I'm really a great believer in Mahler's role as a prophet of the 20th century,” Alsop says, “which was something [Leonard] Bernstein spoke to me a lot about. Bernstein looked at Mahler as having the ability to almost anticipate what was going to happen in the world. Lenny looked at the Sixth as a precursor of the Nazis' rise to power.”

It's easy to hear such a scenario, or myriad others, in this symphony. That's part of what makes it so gripping.

Some of the subtlest moments are the most powerful, such as the cowbells that Mahler introduces in the opening movement and to equally compelling effect in the Andante.

For Mahler, who retreated to the quiet of the mountainous countryside to compose, the bells had great meaning. As musicologist Philip Barford writes: “All wanderers on the Alpine heights know this sound. The higher one ascends, the more remote the tintinnabulation, and the greater one's sense of detachment from the everyday world.”

In the Sixth Symphony, any such detachment doesn't last long. The music inevitably brings us back to earth and all its trials.

“Every note seems to have philosophical overtones,” Alsop says. “This is Mahler's profound search for meaning in life. We have to remember he was living at the time of Freud. Mahler was willing to look at everything, every dark crevice of the subconscious.”

It has been almost 25 years since BSO audiences have had a chance to experience that search. The orchestra's first Sixth came in 1978, with Sergiu Comissiona conducting. David Zinman programmed it in 1986 and again in 1992, when the hammer blows received an electronic boost from a MIDI synthesizer. “We used a sample of a thunderclap,” Locke says. “That was pretty neat.”

This week, the sound will be all-natural.

Locke had help on the design from quantum physicist Christopher Monroe, who teaches at the University of Maryland and also plays percussion in the Columbia Orchestra.

Starting with a crate used to ship a laser, Locke fashioned a large cabinet with a reinforced top. The prototype didn't survive the onslaught of Prechtl's first whack, but the final version held up firmly when tested a few days ago. “It has to be the most man-hours ever devoted to producing a single note of music,” Prechtl says.

That effort is understandable.

“I want it to be a huge blow, so people will actually feel it in the hall,” Locke says. “I don't want it to be a let-down. Our passion for Mahler and the music is the driving force behind this. We love this symphony. It's one of those pieces that sticks with you. You look forward to the next opportunity to play it or hear it. It's a highlight of the season for us.”

tim.smith@baltsun.com