The term compensating is one that is often referred to but not always fully understood. It is normally used with reference to lower brass instruments (eg. Euphoniums & Tubas) which are either 'compensating' or 'non-compensating' models. There is a common misconception that if an instrument has a 4th valve* it is compensating, but that is not necessarily the case. I'll try to explain exactly what it means as clearly and concisely as possible, although that's easier said than done!
The term compensating is one that is often referred to but not always fully understood. It is normally used with reference to lower brass instruments
Willson 2900-TA-1 Compensating Euphonium
Euphonium - Wikipedia
Find many great new & used options and get the best deals for Brushed Brass Bb Compensating system Euphonium Horn with case at the best online prices
Brushed Brass Bb Compensating system Euphonium Horn with case
XO JBEXO1270S Euphonium Bb Compensating with 15-16.8 mm Bore, 310
What is a Compensating Brass Instrument?
Brass instrument - Wikipedia
Besson Imperial Four Valve Compensating Euphonium GREAT PLAYER
Normans Musical Instruments Blog – Tagged Technical Guides
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Mack Brass EU1150 3+1 Valve Compensating Euphonium - musical