Philip Pickett, 64, carried out the assaults while he was a teacher at London's Guildhall School of Music and Drama, British media reported today.
Pickett was found guilty at the Old Bailey on February 10 of two rapes and two indecent assaults on his victims between 1979 and 1983, the BBC said after the court lifted reporting restrictions.
He lured vulnerable pupils into practice rooms, where no one would hear their screams as he shut the door, turned out the light and assaulted them, the court was told.
The first victim, who was 16 at the time of the attack, went to the school in 1978 as a sixth-form student to learn the recorder with Pickett.
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After he was arrested over the 1978 assault in August 2013, more women came forward, resulting in charges relating to two more victims, who were aged 21 and 17 at the time.
The rape of a 21-year-old woman, the rape and indecent assault of the 16-year-old, and the indecent assault on a 17- year-old were offences that all aggravated each other, the judge Charles Wide said.
"Even if they shouted, they could not be heard, as you knew well, having got them on their own and shut the door.
"The impact of these very serious sexual offences must have been very great indeed."
He ordered that two further indictments relating to allegations by two women dating back to the 1970s lie on file.
But the judge rejected it, saying he had his "head in the sand" and had carried on as if nothing had happened.
"He taught for 25 years and travelled extensively abroad doing his concerts with young women musicians so I think there is a high possibility of there being other victims out there," said Detective Superintend Maria Woodall, the lead investigator in the case, outside the court.