There are many counseling service professionals (professional counselors, therapists) that need speech privacy in their offices (examination rooms):
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Many professional counsellors and therapists operate from home offices or small clinics, where maintaining a high level of privacy is essential. Effective soundproofing in these spaces ensures that confidential conversations remain secure and that clients feel comfortable discussing sensitive matters. Proper acoustic design is therefore a critical component of creating a professional, confidential, and functional environment.
Quantitative Sound Insulation Objectives for Speech Privacy
Levels of speech privacy in closed rooms are specified in ASTM standard E2638-10. This standard defines Speech Privacy Class (SPC) as a single-number metric for quantifying degrees of speech privacy as follows:
category | SPC | Description |
|---|---|---|
Minimal speech privacy | 70 | One or two words will be intelligible at most once each 3 minutes, and speech sounds will be frequently audible (at most once each 0.6 minutes) |
Standard speech privacy | 75 | One or two words will be occasionally intelligible (at most once each 18 minutes), and speech sounds will be frequently audible (at most once each 2 minutes) |
Enhanced speech security | 80 | One or two words will be rarely intelligible (at most once each 2.3 hours), and speech sounds will be occasionally audible (at most once each 12.5 minutes) |
High speech security | 85 | Speech essentially unintelligible (at most once in 16 hours) and very rarely audible (at most once each 1.5 hours) |
Very high speech security | 90 | Speech not intelligible and very rarely audible (at most once each 11 hours) |
It is important to note that Speech Privacy Class (SPC) measures speech unintelligibility, not mere audibility. According to reference [1], an SPC rating above 82 is typically required to ensure that approximately 80% of listeners will perceive speech as inaudible.
Most professional counselors and therapists aim for at least “standard speech privacy” (SPC 75). Where feasible, they strive for “enhanced speech security” (SPC 80) to provide a higher level of confidentiality and comfort for clients. Selecting and implementing appropriate soundproofing measures is essential to achieving these targets in home offices or small clinical spaces.
Speech privacy in therapists' offices
As per the ASTM standard, speech privacy is governed by two components:
- 1Sound attenuation of the office walls and door.
- 2Background noise level at the unwanted listener’s location.
The sum of the background noise level in dB at the unwanted listener's position, and sound insulation in dB of the wall separating the listener from the talker, adds up to the required SPC.
An acoustical consultant can measure the sound insulation of a therapist’s office walls, doors, and other partitions to determine whether improvements in soundproofing are necessary.
In many cases, it is possible to achieve adequate speech privacy without extensive construction by increasing the background noise level at the potential listener’s location, such as a waiting room. This technique, often referred to as sound masking, can make conversations inside the office unintelligible to outside listeners, helping meet the desired SPC targets while minimizing structural modifications
In any partition wall, the door is typically the acoustically weakest point. Even a well-sealed, high-quality door generally provides only about 33 dB of sound insulation.
This level of isolation is adequate only if the background noise near the door or entrance is sufficient:
42 dB for standard speech privacy (SPC 75)
47 dB for enhanced speech privacy (SPC 80)
If the background noise is lower than these thresholds, additional measures—such as sound masking or improving door construction/sealing—may be required to achieve the desired level of speech privacy.
Both levels are achievable with a professionally installed sound masking system.
Reference:
[1] ASTM metrics for rating speech privacy of closed rooms and open plan spaces. NRC research paper by B. Gover & J. Bradley
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