Used for sound attenuation, Ceco Door Sound-Tech Xpress(+) and Curries Quiet Noise(+) door and frame systems consist of 2 flush single swinging hollow metal doors within single frame forming communicating opening. Cam lift hinges, flat saddle thresholds, and adjustable door bottoms ensure doors seal completely and function easily. Tested to ASTM E90, E1332 and E413 with STC 66 rating, products also carry OITC rating of 46 and comply with HMMA 865 and SDI 128.