Born to a family of academics, in Aalborg, first training as a chemist, he taught physics for several years before starting work as a deaf educator.

The system used a series of handshapes under the chin to show the sounds of speech as one spoke, giving the observer extra information about pronunciation.

He was inventor of the phonoscope, a device whichwas used to demonstrate to deaf students whether the vowel they were making was correct using a gas flame and rotating drum.

In 1903, he completed a doctorate degree on the subject of deaf communication, and was a supporter of various constructed languages, running a society for one, Ido, in Copenhagen.

[2] Johann Ludolph had seven children with his wife, publisher Margaretha Elisabeth [de],[2] including Johan Georg, August, and Peter.

[6] He was one of thirteen children, his siblings including: Forchhammer finished secondary education at Herlufsholm School in 1879,[6] taking a polytechnic examination in Chemistry on 29 January 1885, from which he gained a first grade (1ste Kar.)

[6] In 1903, Forchhammer completed a Doctor of Philosophy degree at the University of Copenhagen, defending his thesis "On the Necessity of Safe Means of Communication in Deaf-Mute Education.

Med Tilbageblik paa egne tidligere Arbejder) on 27 June of that year to a panel including Drs Kristian Kroman [da] and Otto Jespersen; he was awarded the degree on 11 July 1903.

[16] At the school in Nyborg, students lived with families in the town, to prevent them from signing in the school dormitories [19] – at the time, use of sign language was considered negative in Danish deaf education; his later mouth-hand system afforded a freer style of education to deaf students, and a form of communication less strenuous than speech.

[23] In 1903, Forchhammer created a manually coded language (a signed representation of phonetic speech) to help students learn Danish,[24] which he named the Mund-Hand System.

In a 1935 report from the Occidental-language magazine Cosmoglotta by Ilmari Federn [es], Forchhammer stated that he considered Occidental and Novial to be different dialects of the same language, "Jewahli", and considered himself a "Jewahlist": He found Novial grammar to be more regular and easy to memorise, but preferred de Wahl's handling of the genitive case.