The term 'make quieter' can be solved by two six-letter crossword solutions: 'MUFFLE' and 'DEADEN'. MUFFLE means to reduce the intensity of sound, usually by wrapping something around it or putting a barrier between the source of the sound and the listener. DEADEN means to make something less intense or less effective, often by dulling or numbing it. Both terms refer to reducing the volume of sound, making it quieter.