The PolySupraPlus SDS 2491 is a special modified HW251N with a dynamic noise canceling microphone for super clear, uninterrupted voice transmission. It has a Plantronics quick disconnect (QD) end*. This headset is design for important, mission critical applications. 

Poly Supraplus SDS 2491 Binaural Headset Features:

• Built and designed for mission-critical use and comfort. Special Plantronics engineered dynamic microphone with noise canceling and extended boom blocks nearly 75% of unwanted background noise, ensuring excellent transmission clarity in busy, noisy setting.
• Cable and Quick Disconnect. Single-cable design with robust PU (polyurethane) jacketing material and Quick Disconnect options. Excellent audio quality. Extended frequency response improves intelligibility
• Compatible with All Poly/Plantronics H-series M22 Vista amplifier or bottom cables
• Poly SupraPlus Circumaural Leather Ear Cushions (sold separately) is also available to further reduce the background noise for the user.
• call for availability (special order, not returnable)
• Replaces item# 92491-02