A SOARING sculpture. An instantly recognisable symbol of Sydney. The beautiful building on Bennelong Point is many things, but not a successful opera house. Half a century after the Danish architect Joern Utzon won the competition to design it, and 35 years after it opened, Sydney is still wrestling with the question of how to make its opera house sound as good as it looks.

The Opera House was doomed from the start: Utzon had been given an impossible task. The brief called for "a large hall" to stage both symphony concerts and large-scale opera. That was never going to work. Concert halls and opera theatres need different acoustics and different facilities. So the big shell became the concert hall, and opera was relegated to the smaller shell, which had been envisaged mainly as a drama theatre.

Now there are plans to rebuild the opera theatre inside the Opera House to overcome its lack of space and other problems. The plans call for structural work that is the big item in a makeover mooted to cost as much as $700 million. For that sum, Sydney could build a new opera theatre somewhere else.

When that idea was floated last month in the Herald, there was a roar of support, and some criticism. Many wanted a new opera theatre, and had firm ideas on where to put it. Others wanted to evict symphony concerts from the Opera House and build a concert hall elsewhere. Then opera could be at the heart of the city's most famous building, and the Sydney Opera House would at last be true to its name.

The architect Ken Woolley has gone one better, with a proposal that would allow the Opera House complex to stage the grandest of grand operas without remaking either the opera theatre or concert hall. His idea is to build a 1800-seat opera theatre next to the Opera House, partly over the harbour and partly into the Botanic Gardens. He says this could be done for $400 million.

Woolley admits his idea will not appeal to all. "Some critics will feel it compromises Utzon's original vision, while others will say it just will not work … It does demand courage. Only the brave would dare build something near the sacred monument."