A tuba.
It can be either, depending on how well you can play it. In general, a Trombone is a bass instrument, playing in the bass clef, making it a relatively low-pitched instrument.
A low-pitched brass instrument other than the tuba is the bass trombone. It features a larger bore and a wider bell than the standard trombone, allowing it to produce deeper, richer sounds. The bass trombone typically has one or two rotary valves, which extend its range and facilitate playing lower notes. It is commonly used in orchestras, brass bands, and jazz ensembles.
The most common low brass instruments are: 1. Trombone (bass trombone is lower than tenor trombone) 2. Euphonium & baritone horn 3. Tuba
Trombone. Or, since you specified bass a bass trombone.
Trumpet, Trombone, Baritone, Tuba... That's all I got
Each one of the Brass instruments have a different vocal range. The trumpet is a soprano to alto instrument. (You can bet bass trumpets but they are rare.) The Trombone is a tenor or Bass. French horn or the English horn are Tenors. Euphoniums are bass to tenor. The Eb Bass Tuba is a bass instrument. Sousaphones are bass to double bass.
It is just the same as a regular trombone but with a extra tube which allows the instrument to reach the lower notes. The extra tube is added by means of a rotary valve operated by the player's thumb. A typical bass trombone is a B-flat F trombone. Some older bass trombones were tuned in F or G. These had a long slide which needed a handle to enable the player to fully extend the slide. The G bass trombone was great favourite with the brass bands in England and were still in use well into the 20th century.
Lower brass (ie: trombone, tuba, and euphonium), lower strings (ie: cello and bass), and lower woodwinds (ie: bass clarinet and bassoon) Left hand (mostly) piano also uses bass clef
Rule of thumb: Brass instruments look like they're made of brass. Think Trumpet or trombone, the exception being saxophone, which is a woodwind instrument. An oboe is also a woodwind instrument.
The trombone is the only instrument in the brass section with no keys or valves. It only has a slide.
Bass trombone
trumpet, cornet, Eb Bass, Eb horn, baritone, trombone, euphonium, ETC. Actually, it depends on your definition of "brass band." There are New Orleans Brass Bands, Regimental Brass Bands, both of which encorporate woodwinds. If you're talking about the traditional British Brass Band, the standard instrumentation is: Eb Soprano Cornet, Bb Cornet, Flugelhorn, Eb Tenor Horn, Bb Baritone, Euphonium, Tenor Trombone, Bass Trombone, Eb Bass, Bb Bass and percussion.