Ultrasonic Model HB-650 ear muffs boast noise reduction rating of 29 dB. Provide full-spectrum and low frequency attenuation. Fork-style headband distributes pressure evenly and improves balance required for extra deep ear cups. Flat-Liner Model HB-640 ear muffs attenuate most frequencies from 500 to 4,000 Hz. to about the low to mid-30 dB. range, allowing voice communications in noisy environments up to 100 dB. Steel headband withstands temperature extremes.