The GRAS 45BC head and trunk mouth simulator was introduced by Knowles in 1972, and quickly became the industry standard for hearing aid manufacturers and research audiologists (visit KEMAR.us to read the full text). Grasskemar has the same size and acoustic characteristics as the original KEMAR of 1972, and 100% is backward compatible. When equipped with an auricle simulator, an ear canal extension device and an ear simulator conforming to IEC 603 18-4 or low noise standards, KEMAR can closely imitate the acoustic characteristics of human ears. KEMAR equipped with oral simulator can also simulate the characteristics of human mouth, so it can be used to test communication equipment including microphones and speakers. The acoustic characteristics of 45BC KEMAR with mouth simulator are the same as those of 45BB KEMAR without mouth simulator, except for the slight difference caused by the slightly opened mouth of 45BC KEMAR. 45BC KEMAR conforms to the international standards stipulated in IEC: 603 18-7 and ANSI:S3.36 and S3.25, and is based on ITU-T P 58.