When sourcing soundproof wall boards, the most critical metric is the Sound Transmission Class (STC) rating; for effective noise insulation, look for an STC rating of 50 or higher. Additionally, evaluate the Noise Reduction Coefficient (NRC), which measures sound absorption within a room—0.75 to 0.95 NRC is ideal for recording studios or offices. Ensure the material density is high, typically above 12kg/m³ for polyester fiber or 80kg/m³ for rock wool cores, to effectively block low-frequency vibrations.