We have better technology than that: a mini-camera mounted to the front of the bell with a suitable display on the rear of the bell (attached to an adjustable mechanism so it can be correctly positioned for the individual player's preferences). Better, perhaps: a totally wearable set of goggles that show both the conductor and the music -- perhaps with the music overlayed on top of the conductors image so it can be seen through the music. I can almost feel a patent here.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)