An artist's impression of the revamped Concert Hall at the Opera House. On Thursday, Deputy Premier and Arts Minister Troy Grant unveiled working designs for the biggest upgrade to the Opera House since it opened in 1973. The hall, which has hosted concerts, cabarets and even circus acts, is the largest of six venues housed under the white sails and will be closed between August 2019 and January 2021. "The problem is with the very high ceiling a lot of the sound that the orchestra actually makes rises and isn't reflected down, so that the musicians on one side - for example the second violins - have trouble hearing the double basses," said Sydney Opera House chief executive Louise Herron. "It means, it's not such a good experience as it could be if the sound is more contained."

"I was hearing the orchestra for the first time": chief conductor David Robertson. Credit:Jay Fram The infamous "glass donuts" above the stage and the "ugly marquee" outside will both be removed. A new acoustic ceiling will be installed with reflectors that can better distribute sound. The stage will be lowered and the back of stage expanded. An air conditioning system for the foyer - the size of four shipping containers - above the ceiling will be removed. A new air conditioning system will be installed under the seats. The working designs - which still need to be fine-tuned - include three lifts, an escalator to the foyer, more passageways, a new function centre, expanded seating areas outside the hall and wheelchair seating areas within.

"We need to make it as accessible as we can," said Ms Herron. "So it will make a difference to have a creative learning centre, remove the ugly tent, and all those things, so people feel more of a sense of ownership, and can be prouder of the Opera House," she said. "A lot of the equipment is ... old and anyone knows that technology has moved a long way and has worked really hard, so that needs to be replaced." The Melbourne-based firm ARM Architecture is behind the designs. The orchestra's managing director Rory Jeffes said they have been closely involved in the development of the designs, and the musicians were excited about the improvements.

"It's been a fabulous home for the orchestra for the past 40 years ... for the first time, the hall will deliver what it is that the original fathers who produced this incredible building wanted," he said. "But for me the real winners will be the audiences, people will be able to come and sit and enjoy the greatest orchestras in the world right here in this hall with one of the greatest acoustics in the world." The $202 million Concert Hall upgrade is funded by the the state government, whereas the bill for the Joan Sutherland Theatre renovations will be covered by the Opera House. The theatre will be closed for seven months from May next year. The Opera House cost $100 million to build, but the "cultural and iconic" value of the Opera House is $4.6 billion.

Mr Robertson, the chief conductor, compared the hall to the Hubble Space Telescope. Loading "[At first] breath taking images and very inspiring, but nothing like the fix that happened, when they actually got the mirror focused," he said. "We were suddenly able to see all sorts of details... [and with the upgrade] it's the details that allow the music to come through in all of its clarity and I'm incredibly excited."