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  • Tony Hoover

STC – role in Speech Privacy

By: Tony Hoover, MCH Principal


The STC (Sound Transmission Class) rating of a partition is an important factor for speech privacy, it is but only one of several factors for addressing speech privacy goals.

The four most important factors are:

Speech Level of the “Source” (the talker)

We generally categorize speech levels as “normal”, “raised”, or “loud”. Loud speech (roughly 72 dBA) will be more audible, with less privacy, than normal (roughly 60 dBA).

Sound Isolation - STC

A partition’s sound isolation between the Source and Receiver is summarized by STC, with higher values blocking more sound. Partitions can be designed for a wide range of performance, typically STC 40 up to STC 65. Doors, windows, and other elements may block considerably less sound, so the entire construction should be considered.

Background Noise Levels in the “Receiver” (the listener) room

Background noise levels in “Receiver” rooms, usually from the HVAC system, provide “masking” of the speech sound. Extremely quiet background noise levels can lead to privacy issues, because even quiet transmitted sounds might be audible. Sometimes, electronic sound masking systems can be useful to enhance privacy.

Expectations of the Occupants

Privacy expectations need to be considered. Privacy levels are often described as “Normal” or “Confidential”. Normal privacy usually means that understanding portions of other people’s conversations is generally acceptable, but confidential privacy means that almost nothing should be understandable outside the Source room.

All four factors must be considered as a system, in order to address speech privacy goals.

For example:

STC 45, background noise 35 dBA – acceptable for normal privacy, normal speech.

However, for confidential privacy for the normal speech, increase STC to at least 51 -or- add masking to at least 41 dBA.

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