Abstract: A brass instrument having a mouthpiece connected by a pipe to a valved body which is in turn connected to an output bending and a bell thereby defining an air duct. The bell and the output bending are formed of separate and detachable parts. The brass instrument has an intermediate section between the output bending and the bell and a coupling member for detachably coupling the intermediate section to the output bending and to the bell respectively. The intermediate section has a plurality of subsections in telescopic relation to one another and parts for adjusting an overlap between the plurality of telescopic subsections so as to change a length of the intermediate section whereby to alter a tone of the instrument.