Operable Walls & Sound Masking
22 April 2021
The lab-proven ability of an operable wall to block noise is the second most common selection criteria for customers. The first factor? Price. However, soundproof operable walls don’t exist.
If partition assemblies are imperfect—and laboratory performance indicators such as STC and NRC aren’t completely reliable indicators of what to expect in the real world of acoustics—what’s a consumer to do?
Clients want—and need—closed rooms to provide speech privacy and noise control. Walls alone don’t often ensure these results, even when performing perfectly to spec. Hearing noise or conversation from an adjacent room isn’t only based on the wall’s ability to block noise, but on two factors in the listener’s location:
- the level of unwanted noise/speech
- the background sound level
When the first is higher than the second, noises are audible and conversations intelligible.
All speech intelligibility measures, including ASTM E1130 and E2638, consider background sound levels when calculating speech privacy. The predictive Speech Privacy Potential (SPP) tool states that the sum of the room isolation and background sound level (dBA) must be 75 or more to achieve confidential speech privacy. Privacy is agreed to be mutually dependent on isolation and background sound levels.
The questions becomes: how can intruding noise exceed the background in a well-built space?
Firstly, a room’s isolation performance depends not just on walls, but on its entire construction. The composite STC (STCc) derives from the blocking performance of walls, ceilings, windows, doors, HVAC, joints/seals, and any penetrations. Sound not only passes through the wall, but flanks it via these other elements. The lowest-performing element determines how much noise passes from one room to the next.
Secondly, ambient sound levels are typically low and unreliable. Designing for background sound levels is often ignored, because they’re commonly considered an uncontrollable outcome of other design choices. Background noise sources (e.g. building systems) are, in fact, also highly inconsistent—from room to room or moment to moment—leading many to conclude that only the lowest levels may be relied upon. STC guidelines are based on this unspoken assumption.
To deal with a sound leak issue, it is best to deal with it during the design phase a project rather than after the fact. This means not just considering the STC rating of the operable wall but everything around it as well.
Read more about sound masking here