Never underestimate the tuba’s enormous powers of projection.
Tuba is one of those instruments that gets overlooked quite often by beginning orchestrators, or added to a score as an afterthought – a little bit of extra weight here or there for the heavy brass. Actually, it’s quite a fascinating instrument, with great potential for interest in a score.
The tuba has a different construction than most other brass. It’s a “whole-tube” instrument – that is, its whole length is used for creating a tone, and it’s an entirely conical instrument. This means that it speaks rather easily, just like the bugle and the saxhorn (also whole-tube instruments). This ease of tone is balanced by the huge amount of air needed to sustain a pitch. Try blowing out a match held at arm’s length – that’s the kind of focus of breath needed for effective tuba playing.
Just for comparison, trumpets, trombones, and even horns are “half-tube” instruments. That means that the first section of bore is cylindrical, and the second section flares. The extent of the flare, called “stepping,” determines the ultimate timbre of each instrument. Half-tube design diminishes the playability of the fundamental harmonic position, while making the upper partials more secure.
With a tuba, though, the fundamentals or “pedal tones” are the whole point – the lowest partials are emphasized because of the design. This also gives the tuba more power than you might realize. A tuba playing a prominent line fff can easily be heard over the sound of the rest of the orchestra. It’s easily the heaviest of the heavy brass in tone weight, and rarely needs help in emphasizing a low note.
In the following excerpt from the first movement of Mahler’s Symphony No. 3, note how the dynamics are written for the bass instruments from figure 9. The cellos and basses are playing a fp articulation, sometimes with dim. This is doubled by contrabassoon for the double basses. However, look at the tuba. It’s doubling the cellos an octave higher than the contra and the basses, but it’s playing a simple backwards hairpin. This means that its tone will dominate the entire bass line.
The reason why is simple. It’s dynamically matching the triple unison F trumpets right above it, who are essentially playing a “blue note” resolution from concert C# to D. This would be up a 10th from the first tuba Bb. If the tuba were to play a fp articulation, it would rob the trumpets of harmonic support. So the tuba plays a balancing act here between the emphasis of the downbeat and its own position as part of the brass section. It wouldn’t be out of place for a slight tenuto at the start of each note, to clearly bond the tuba with the other low players.