The Royal Opera has lost its appeal because of hearing loss that has changed the life caused by Violin at the Vagner's Die Valkure trial.
The Court of Appeal unanimously ruled that ROH had not taken reasonable steps to protect Christopher Goldscheider during the 2012 rehearsal.
The court also failed to respond to dangerous levels of noise until the grievance of Mr. Goldscheider, the court ruled.
ROH said it was "disappointed" with the aspects of the court's decision.
Last year, Goldscheider won an important case of the High Court, which was challenged by ROH.
In that case, Mr. Goldsider sued the London opera, seeking compensation for acoustic shock – a condition with symptoms including tinnitus, hyperacusia and dizziness – after exposure to a noise exceeding 130 decibels.
In his appeal, ROH claimed that the artistic value of music produced by the orchestra meant that some damage to the hearing of his players was inevitable and justified – but the court dismissed it.
September 1, 2012 Goldscheider was seated directly in front of the tangled orchestra section of the Vagner's thunderous opera Die Valkure in the famous orchestral opera house of Covent Gardens.
The bell of the trumpet was right behind his right ear during the rehearsal, and the noise level reached 132 decibels – roughly equivalent to the jet engine's power.
His hearing is irreversibly damaged. Mr Goldschadzer of Bedfordshire now has to wear ear protectors to perform daily housework such as preparing food.
Speaking after an appeals court ruling on Wednesday, he said: "I am grateful to the court for acknowledging that it was necessary to do more to protect me and other musicians from the risk of persistent and changing hearing problems.
"We all want to find a way to participate and share the experience of live music in a safe and accessible way and I hope that the instructions given by the Court of Appeal in my case will help others. I hope that the Royal Opera House will now support me to continue the restoration of my of life. "
Clive Coleman, a BBC correspondent
In terms of protecting people from hearing loss due to noise, this case efficiently brings the space of the orchestra – or any live music station – in accordance with other operating environments such as the factory floor. The space of the orchestra or the place of performance becomes, if you like, the factory where the noise is the final product, not the byproduct of the industrial process.
Since no classical musician sued an acoustic shock orchestra before the g. Goldsider, it became a bribe that the orchestras and rooms for live music were free of noise protection.
This myth is partially fed by the defense available to employers in accordance with the Compensation Act. It is effectively said that the product (that is, music) is of high artistic importance, that some noise from the noise for those who produced it was acceptable.
But the judgment of the Appellate Court sets that myth to rest. Employers and organizers will now have to establish noise assessment processes and anticipate a sudden increase in noise levels. They will then have to take all reasonable practical steps to prevent injuries caused by noise. Music will not stop, but it could be a little quieter.
Alek Beard, executive director of ROH, said he was pleased that the court accepted his argument that it was not "reasonable to make orchestral musicians wear protective tools all the time while performing and practicing."
Such a move, as recommended in the original judgment of the High Court, would be "completely impractical with potentially devastating and far-reaching consequences for the entire sector," he said.
He said ROH will work with his legal team to consider his next move.
"This is a case of unprecedented and unusually complex for the live music and theater industry and we will continue to work with other cultural institutions to encourage and apply best practices across the sector," added Mr. Beard.
"Implications of Live Music"
Mr Goldscheider's lawyer, Chris Fri, said: "Live music and high-quality art production can be destroyed by converting sound to noise.
"I can choose to reduce the volume and other settings if I listen to it privately, but such a luxury was not for Chris Goldscheider and many other musicians who require someone else to dictate the noise they are exposed to at work."
He said hearing protection "is not always practical" and that "it was never intended to be a complete solution".
"The court's emphasis on reducing noise at source will have implications for live music, entertainment and sports in various jurisdictions where there is potential for sudden and unexpected noise," he added.
G. Goldsider began playing the violin at the age of five, and Viola from the age of 21. He studied in Prague and the UK and played with the Royal Philharmonic in Liverpool and BBC symphony orchestras.
In 2002, he joined the violin part of the ROH Orchestra as a number of violins and was promoted to number six. The career included playing on stage with Killa Minogue and with three tenors to 100,000 people in Barcelona.
He left ROH in July 2014 as a result of an injury.