akB Conference Management Ltd director Ali Copeman told the meeting, called by the Dunedin City Council to hear the public's views on the project, she struggled to run conferences with the facilities in the city.
"We've had to take too many conferences away from Dunedin."
The meeting of about 45 people, including nine city councillors, was chaired by businesswoman Barbara Henderson-Wragge and attended by Dr Diane Brand, from Auckland University's school of architecture and urban design.
Dr Brand wrote a peer review of the project to build an atrium on to Harrop St which suggested any extension be smaller and that the land between the Dunedin Town Hall and St Paul's Cathedral be turned into a public space.
Hands off Harrop founder Judith Medlicott questioned the need for more "crush space" - one argument for the atrium to be built.
Dr Brand said it would be needed by groups not represented at the meeting, and those groups would help bring revenue to the facility.
Mrs Medlicott questioned the need for more space when the Awatea St stadium would have conference space.
Ms Copeman said there would be a cost for conference organisers to set up in the stadium.
Multiday conferences needed four or more rooms in the same building that could hold 100 people.
She said she supported "option 13" - digging out the basement of the Dunedin Centre to create foyer space and moving the building into the Municipal Chambers, rather than the atrium.
