Ken Leginchin's Mirafone contrabass trombone, at left, pitched in BB-flat (the same as the typical tuba used in a band), contrasts with Glen Newton's alto trombone, pitched in E-flat, an octave plus a perfect fourth higher. The contrabass and alto trombones were the largest and smallest trombones used in the Minneapolis Trombone Choir's February 27, 2005, concert.

Don Dresser and Ken Leginchin pause for a picture before the start of the Minneapolis Trombone Choir concert. Don, at left, displays his Olds bass trombone, whose fundamental pitch is an octave higher than that of Ken's contrabass trombone. Despite the difference in tubing length, and despite having a bore (inner slide diameter) of 0.635" vs. 0.562" for the bass trombone, the bell sizes are nearly the same. The contrabass trombone bell diameter is 10 inches, and bass trombones typically have bell diameters between 9.5 inches (as shown here) and 10.5 inches.

Whereas higher-pitched trombones have two legs to the slide, the BB-flat contrabass trombone has four, arranged like a double slide. The slide positions are basically the same as on the bass trombone, despite the contrabass' double length, because changing the slide position on the contrabass moves four slide tubes, rather than two. The relation of the slide positions to the end of the bell is different on these two instruments because the bell of this model contrabass is positioned farther toward the rear for better weight balance.

A potential problem with the double-slide instrument is emptying the moisture that collects in the slides. Ken's instrument was made with a water key on one of the slides, but moisture collects in both slides. The instrument is too unwieldy to rotate like a French horn to remove moisture, so Ken added a second water key, on the other slide.

This contrabass trombone has a single rotary valve, which lowers the pitch by a perfect fourth, performing the same function as one of the two valves on the bass trombone. The double slide is only long enough to reach 6th position, so the valve is essential for playing B natural or low E natural, as well as for the extended low range.

This contrabass trombone is played with a tuba mouthpiece, which facilitates playing the low notes. However, the instrument has much less resistance than a tuba, so Ken uses a mouthpiece with a small throat that was made for an F tuba, to provide some resistance. Despite this, Ken reports that the contrabass trombone requires more air than his large tuba.