Walkers Ultimate Digital Quad Connect Electronic Earmuffs Bluetooth (Grey) NRR27. Bluetooth Sync w/ Mobile Device. Independent Volume Control – For Bluetooth signal and external mics to control the desired volume of wireless signal separate from ambient sound. Full Dynamic Range HD Speakers for clear balanced sound. Low Noise / Frequency tuned for natural sound clarity. Sound Activated Compression – 0.02 second reaction time. Continue to have normal conversation while protecting against dangerous noise levels.