When the Nashville Symphony presents Vienna Old and New on April 9-11 in Laura Turner Concert Hall, audience members might want to pay special attention to the brass players during Anton Bruckner’s Symphony No. 7. Expansive in scope and dramatic in effect, this piece will also feature two instruments not typically seen on the American concert stage.

Most unusual of all is the Wagner tuba, named for the celebrated German composer, who developed this instrument to enhance the brass section in his Ring cycle. Though Wagner sought to create an instrument that would fall somewhere between a French horn and a trombone, the Wagner tuba is often described as a combination of a French horn and a tuba, with a sound that somewhat resembles a euphonium. “It’s very unusual,” says the Nashville Symphony’s associate principal horn player, Joy Worland, one of four musicians who will play the Wagner tuba at this month’s concerts. “The sound is very mellow and beautiful.”

When Bruckner penned his Seventh Symphony, he wanted to pay tribute to Wagner, whose music had a profound effect on the younger composer, and the Wagner tubas allowed him to do just that. At the time, Bruckner had learned of Wagner’s illness and death, and the second movement of his symphony became an expression of mourning. At the opening of the movement, the quartet of Wagner tubas play a prominent role, lending the piece an elegiac tone.

These instruments can be awkward and difficult to play, owing in part to their construction, but when they come together, as they do in Bruckner’s Seventh, the effect is stunning. “They have this sort of haunting quality,” Worland says. “It’s really different from hearing four horns playing together.”

Because the Nashville Symphony uses them so infrequently — only once a year, or every other year — the orchestra rents Wagner tubas when a score calls for them. For this performance, the Wagner tubas are being provided by the Dallas Symphony.

While the Nashville Symphony’s horn players explore the unique sonority of the Wagner tuba, the orchestra’s trumpet section — Patrick Kunkee, Jeff Bailey and Gary Armstrong — will be playing the orchestra’s three rotary trumpets, which look and sound different from the trumpets audiences are used to seeing.

In a conventional trumpet, also known as a piston trumpet, the three keys work much like a piston in a car — moving in an up-and-down motion. When a player presses one of the keys, the piston lengthens or shortens the flow of air, which in turn changes the pitch of the note. A rotary valve trumpet, meanwhile, more closely resembles a French horn: The instrument appears to be held sideways instead of upright, and when pressed, the keys turn valves that control the air flow through the trumpet’s tubing.

Eye-catching they might be, but these trumpets also effect a simple yet profound transformation in the orchestra’s overall sound. “It’s a question of the timbre,” explains Bailey, co-principal trumpet for the Nashville Symphony. “Rotary trumpets blend more smoothly with the other brass instruments, while piston trumpets tend to sound brighter and cut through the orchestra. When we’re playing the piston trumpets onstage, the top notes stand out more prominently.”

Rotary trumpets are much more common in Europe, where many orchestras rely on them in the same way that American ensembles have typically relied on the piston trumpet. Over the past couple of decades, that trend has changed, as more stateside orchestras have begun working the rotary trumpet into their instrumental lineup with greater regularity. The Nashville Symphony acquired its own rotary trumpets, made by the Austrian company Musikhaus Karl Schagerl, thanks in part to a generous donation from state Sen. Douglas C.H. Henry through The Tennessee Trust.

These days, the orchestra’s trumpet section employs both types of instruments. “I sit down with the trumpet section, and we all discuss together which instrument makes sense to use on a particular piece,” says Giancarlo Guerrero, the Nashville Symphony’s Music Director Designate. “This is fantastic, because it gives us so much flexibility, and it really shows the trumpet players’ commitment to the composer and to the music.

“These instruments are great for Bruckner, because he was an organ player, and that shaped his own approach to composing — he was thinking about all the sounds coming from the organ pipes without any particular one leading the way. So in this piece, you want the brass sound to be blended, and the rotary trumpets are perfect for that.”

By the same token, certain pieces beg for a piston trumpet, and audiences can count on hearing that piercing, much more distinct sound when the Nashville Symphony undertakes a Mahler symphony or The Great Gate of Kiev from Mussorgsky’s Pictures at an Exhibition. The choice of piston vs. rotary all depends on what each particular occasion demands.

For Bailey, part of the trumpet player’s job is to find just the right sound for whatever he’s playing. It’s for this reason that he owns no fewer than nine trumpets, each different from the other. “I equate it to being a professional golfer,” he says. “Your swing might be similar no matter what you’re using, but you’d better know how to hit with every single club in the bag.”