Positioned beneath the building's iconic dome in Boston, the Massachusetts State House Senate Chamber traces its origins to 1795, when Charles Bulfinch designed it as the original meeting place of the House of Representatives. CBT Architects led the 2018 renovation of the Chamber that would return the space to its 1898 appearance while simultaneously equipping it for 21st-century legislative work.

The domed ceiling presented a fundamental acoustic challenge, where hard, curved plaster surfaces collect and focus sound energy, generating acoustical reverberation that can undermine speech intelligibility. The goal was to introduce sound absorption across the dome surface without disturbing the visual character of the space.

The selection process for the acoustic ceiling treatment evaluated multiple acoustical plaster options through physical mock-ups and acoustical testing. The 30 mm BASWA Phon Classic Fine acoustical plaster system was ultimately selected on the basis of acoustic performance, delivering an NRC of 0.80 as lab tested.

Installed by Angelini Plastering, the BASWA system was color-matched to the original dome color to remain invisible within the historic medallion ornamentation. The result is a system that absorbs sound and returns clarity to speech across the chamber floor and gallery.