Interesting case, though not entirely clear it sets a clear precedent. What is a bit distinctive is that he is a viola player and this was, as near as one can tell, his primary source of income, with not much else available in the way of gainful employment for viola players. (Look in listings of musician jokes and there are probably as many about viola players as there are for accordions).
What is a bit of a head-scratcher is just exactly who bears responsibility for the SPLs that damaged his hearing. Obviously it's the musicians making the racket, but it is also the conductor waving the stick that makes things louder. My younger son played trombone in his high school's concert band, and the trombones were always seated directly in front of the drummer, who was loud and rather rhythm-challenged. Should the closest source of loud sound be to blame for his hearing loss? My sense is that, the burden of responsibility was passed on to the employer, being the ROH, simply because they were the employer. The court seems to have treated it like what would happen if a ballerina fell off the front of the stage, or a guest slipped on the ice leaving your front door: your premises, your responsibility. But are they supposed to interfere with the conductor, and direct him/her to "keep it down"? I mean, it's clear that some compensation is warranted because the guy has been blasted out of being able to earn a living, through no fault of his own. But whose fault is it, when it comes to providing that compensation?