The 24 x 24 in PLQ has a square faceplate made of one-piece, nonfolded material with rounded corners to give the diffuser a clean appearance that is unobtrusive to ceiling systems. The single faceplate gives the diffuser reduced pressure drops and a quiet sound profile and is held in place by hooks that lock into the backpan. The one-piece, stamped backpan provides smooth, consistent corners, exacting dimensions, and performance tolerances. The removable faceplate offers easy duct and damper access.