NCIDQ IDFX Practice Exam

A normal speech becomes faintly heard at which STC rating range?

1. 25-30

2. 42-45

3. 35-40

4. 30-35

The correct answer is: 42-45

The Sound Transmission Class (STC) rating is a measure of how well a building partition attenuates airborne sound. In assessing when a normal speech becomes faintly audible, it's essential to understand the STC rating scale and its practical implications. A rating in the range of 42-45 indicates excellent sound reduction qualities. At this STC level, most conversations are likely to be severely muffled, leading to situations where faint portions of speech could be heard, but not clearly. This level of sound isolation is commonly achieved through thicker walls, soundproofing materials, and careful construction practices designed to minimize sound transmission between spaces. In contrast, other ranges, such as 25-30 and 30-35, would allow for more pronounced sound transmission, making conversations easier to hear and less muffled. A range of 35-40 does offer some sound isolation, but it does not provide the same level of attenuation that the 42-45 range does. Therefore, the identification of the 42-45 STC rating range as the point at which normal speech becomes faintly heard aligns with industry standards for effective soundproofing and noise control practices.