The NCIDQ IDPX exam tests the designer’s knowledge of acoustical design, including the metrics used to evaluate a material’s acoustic performance. Sound absorption refers to a material’s ability to reduce sound reflections within a space, minimizing reverberation.

Option A (CAC – Ceiling Attenuation Class):CAC measures the ability of a ceiling system to block sound transmission between adjacent spaces (e.g., through a ceiling plenum). It is related to sound isolation, not absorption.

Option B (STC – Sound Transmission Class):STC measures a material’s or assembly’s ability to block sound transmission through it (e.g., from one room to another). It is used for sound isolation, not absorption.

Option C (NRC – Noise Reduction Coefficient):This is the correct choice. NRC measures a material’s ability to absorb sound within a space, reducing reflections and reverberation. It is expressed as a value between 0 and 1, with higher values indicating better sound absorption (e.g., acoustic panels might have an NRC of 0.9).

Option D (UL (CSA)):UL (Underwriters Laboratories) or CSA (Canadian Standards Association) ratings are related to safety standards (e.g., fire resistance), not sound absorption.

Verified Answer from Official Source:

The correct answer is verified from NCIDQ’s official study materials on acoustical design and performance metrics.

“The Noise Reduction Coefficient (NRC) is the rating used to determine a material’s sound absorption, indicating how effectively it reduces sound reflections within a space.” (NCIDQ IDPX Study Guide, Acoustical Design Section)

The NCIDQ IDPX Study Guide defines NRC as the metric for sound absorption, which directly aligns with the question. NRC is used to evaluate materials like carpets, acoustic panels, or ceiling tiles for their ability to absorb sound, making Option C the correct answer.

Objectives:

Understand acoustical performance metrics (NCIDQ IDPX Objective: Acoustical Design).

Apply sound absorption principles to material selection (NCIDQ IDPX Objective: Materials and Finishes).