Berghaus was his wife Elvira's (1837-1924) maiden name. She was a famous opera singer. He was leader of the second Müller Quartet of Meiningen and Rostock, 1863-73: wikipedia (Eng, Ger) The other members were his brothers Hugo 1832-1886, Bernhard, 1825-1895 and Wilhelm 1834-1897. Wilhelm was the cellist of the Joachim Quartet from 1869 to 79.