5.9 Thermal Mass and Acoustic Absorption

Thermal mass cooling is an important consideration in sustainable building design. Conventional acoustic absorbent materials are added to the soffit of a building, this design therefore clashes with thermal mass cooling. There are two solutions to this problem. The first is to apply the acoustic treatment to the walls, this works but can take up a lot of wall area and can be expensive. It is also important to maintain the acoustic treatment well above finger height, in order to increase the durability and control the cost of maintaining the acoustic finishes.

The second method is to suspend the acoustic treatment. Illustration 1 provides a range of design options which provides both acoustical absorption and thermal cooling.

2 - Acoustic beams can be extremely effective since all six sides of the beams will provide acoustic absorption.

3 - Raft ceilings - it is often the case that 30-50% of the ceiling can be covered whilst still providing the thermal cooling. Rafts of acoustic treatment can therefore be used below concrete soffits.

4 - Suspended acoustic panels - A similar design to that of 2, but in this case, the acoustic panels are suspended on wires.

5- Acoustic light fittings - Perforated metal wings are added to the side of a light. Again, this is an effective method of adding acoustic absorption to a space, since both the top and bottom of the panels provide absorption.

5.10 Acoustic Beams

Suspended acoustic treatments can be an effective way of reducing the reverberation time within a given space, since these forms of acoustic absorption provide absorption from more than one side/surface. Image 6 is Dartington School, A MACH Acoustics project encompassing acoustic beams produced through MACH
Products. To meet BB93 requirements additional 300mm white ceiling tiles run around the perimeter of these spaces.

Type L1 - 800mm wide foil, 48mm acoustic absorption
Type L2 - 800mm wide foil, 30mm acoustic absorption
Type L3 - 600mm wide foil, 30mm acoustic absorption

Type C1 - 6mm needle-felt carpet tile - 0.15 α_W
Type C2 - Carpet tiles with a felt backing - 0.25 α_W
Type C3 - Lino as used within science labs - 0.00 α_W