The whole unit includes a coupler cavity(CRY3719)+ a ½  inch pressure measurement microphone (CRY3202)+a ½  inch preamplifier (CRY3502). 

Acoustic measurements for hearing aid headphones and in-ear headphones, with a variety of sound-guiding chambers to suit different headphones. It is also suitable for conducting electroacoustic characteristic experiments of household and similar appliances, information technology devices, audio, video.