In contrast to direct-field sound masking, alternative indirect-field sound masking solutions (also referred to as plenum-based or in-plenum sound masking systems) use above-ceiling audio speakers to emit random broadband sound in an upward direction.
Installation typically involves placing large amplifiers above vaulting, beams and ceiling tiles. Sound waves reflect off the highest point and back down, through the ceiling tiles, and into the work environment below.
Obstructions above the ceiling (the plenum), such as structural components and HVAC parts, impact how indirect sound masking is led back into the work environment. Subsequently, resulting in volatile and unstable acoustics. For instance, this variety of sound masking can sometimes generate “hot” or “cold” spots – meaning that some areas don’t receive enough masking, while other spaces suffer from excessive masking. In addition, there may also be sound leakage; this unwelcome sound can pollute private spaces that do not require masking.