Measure the ambient noise level in your open‑plan workspace. If your environment is typically 45–65 dB (most active open‑plan offices), the upper‑range Class B ( 28–30 dB) is the optimal specification. If your office is generally below 35 dB (very quiet, low occupancy, extensive acoustic treatment), Class A provides worthwhile additional isolation margin. Class A is also suitable if you work in a regulated industry with formal confidentiality obligations for verbal disclosures.