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Tuesday 30 July 2019 11:52pm

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Raising the acoustic floor … Mason Mercer New Zealand sales engineer Greg Tate holds one of the almost 900 jack mounts cast into the main concrete floor slab in the control room for the main music and performance studio. Photos: Sharron Bennett.

Workers are hand-winding large concrete floor panels into place above slab floors and joiners are crafting more than 780 acoustic boxes for the music and performance studio building under construction behind the Robertson Library in Union Street East.

Both the panels and boxes are for 12 acoustically rated spaces in the building for the University’s School of Performing Arts – they will be in recording studios, control booths, isolation booths, recording booths and percussion rooms, University of Otago Campus Development Division Director David Perry says.

Main contractor Naylor Love is constructing each of those rooms as a carefully sealed ‘box within a box’, to help stop sound and vibrations getting in and sound escaping.

Exterior walls, floors and ceilings need to be bulky to prevent sound transmitting through them, so Baker Garden Architects in association with CCM Architects designed them in concrete.

The interior walls and ceilings are triple layers of plasterboard to also limit sound being transmitted, while the interior floor is a concrete panel, he says.

The interior and exterior ‘boxes’ are separated as much as possible, to stop sound travelling between them, with:

  • An independent steel frame supporting the internal walls and ceiling of the large ground floor studio, separating it by 300 millimetres from the exterior wall and ceiling
  • An independent timber frame supporting the internal walls of other acoustically treated rooms, separating them by 300 millimetres from the exterior walls and ceilings
  • Rubber strips with acoustic foam separating the interior ‘floating’ acoustic concrete floor from the exterior walls, by 20mm
  • ‘Screw jacks’ raising and separating the interior acoustic concrete floors from the main concrete floor slab, by 50mm

To create the acoustic floor, plastic is laid on the floor slab then covered with the formwork and steel reinforcement needed to form and strengthen the acoustic floor, then concrete is poured to between 150-175 millimetres (mm) thick, and left to set for seven days before jacking, Mr Perry says.

Almost 900 jacks with specially designed robust 20mm diameter screws are cast into the concrete floor slab with corresponding grommets cast into the acoustic floors, so workers can remove the grommets, insert what are essentially large screw drivers, and wind up each jack by hand 4mm at a time, to the total separation height of 50mm.

Recently, workers raised three floor panels, of about 25 square metres each, in around three hours.

The largest panel in the building is 150 square metres and was raised yesterday in about three hours, for the ground floor recording studio which includes a control booth and two isolation rooms as well, he says.

Another eight rooms on the first floor are being constructed with the same floors, walls and ceilings – four recording and performance booths, two control rooms and two percussion practice rooms.

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The main studio ... University of Otago Senior Project Manager Steven Ireland looks up at the two storeys of the main music and performance studio in the new building, while (from left) apprentice carpenter James Riach, carpenter Graeme Wall, and carpenter Simon McCaig jack up the acoustic floor in the main control room, to a total of 50mm above the concrete slab floor.

On site, most of the music and performance studio building’s exterior walls are already in place and workers have also constructed some internal walls from triple layers of plasterboard.

The final nine exterior pre-cast concrete two-storey-plus wall panels are being delivered to the site throughout this week for the music and performance studio building.

But those are only some of that building’s special requirements. Joiners off-site are also creating about 780 timber-framed boxes of various materials, shape and sizes – that are 100-250mm deep – to attach to walls in the recording studios, control booths, isolation booths, recording and performance booths, and percussion rooms.

Workers on site will finish off the boxes by adding acoustic fabric, Mr Perry says.

Marshall Day acoustic consultant Markus Schmid says the boxes will determine the acoustic footprint of each room.

The boxes comprise three types of sound absorbers – plain, panel and slotted – and one type of diffuser. To give each room a particular sound for its intended use, these acoustic treatments vary in their shape, distribution and quantity.

Plain absorbers for example are used to attenuate a broad range of high frequencies. The insulation in the box causes energy losses due to friction of the air molecules.

In contrast, slotted and panel absorber are targeted to absorb a specific range of lower frequencies. Depending on material thicknesses and size of air cavities, the sound energy loss is caused by damping in the mass-spring system.

The diffuser boxes prevent sound echoing and sound being reflected back at the same angle. Instead sound is diffracted into various angles by the uneven surface of the diffuser.

Every acoustically treated room is very carefully designed then commissioned once completed to ensure the rooms sound as expected, Mr Schmidt says.

Mr Perry says this $26 million project includes building two new links as well:

  • On the first-floor between the new building and the eastern end of the existing University of Otago College of Education Music Block
  • On the ground floor between the college’s existing Teaching Wing and eastern end of the Music Block

Both links already have a floor, roof and walls, so windows and linings are going in. Preparation work is also starting for installing pipes and wires then plastering (often referred to as Gib stopping) during the next few weeks.

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A look at how the building is progressing on the outside.

As stage two of the project, specialists are removing asbestos in the college’s existing Tower Block and Teaching Wing before work can start on refreshing those areas with paint and some relatively minor alterations.

This project is on track to be completed before the start of the 2020 academic year, Mr Perry says.

Check out this video:

The University’s Campus Development Division is managing this project and is part of the Operations Group, which has three top priorities:

Enable – the University to achieve its visions and mission
Engage – with our students, each other, our customers and externally
Experience – of our students, our customers, and externally to be outstanding

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