Stevens was head of the speech communication group[2] in MIT's research laboratory of electronics (RLE), and was one of the world's leading scientists in acoustic phonetics.

[7] Stevens had been a teacher since his undergraduate years, when he lectured sections of home economics that involved some aspect of physics.

[5] After receiving his master's degree, he stayed at the University of Toronto as an instructor, teaching courses to young men returning from the war, including his own older brother.

In November 1949,[8] the office next to Ken's was given to a visiting doctoral student from Sweden named Gunnar Fant, with whom he formed a friendship and collaboration that would last more than half a century.

[11] Ken credits Fant with the association between the Linguistics Department and the Research Laboratory for Electronics at MIT.

[5] After receiving his doctorate, Stevens went to work at Bolt, Beranek and Newman (now BBN Technologies) in Harvard Square.

[5] In the early 1950s, Beranek decided to retire from the MIT faculty in order to work full-time at BBN.

Stevens is perhaps best known for his proposal of a theory that answers the question: Why are the sounds of the world's languages (their phonemes or segments) so similar to one another?

This second stage is mainly experimental, where tokens of interest are usually recorded either in isolation, and/or embedded in a controlled carrier phrase, usually spoken by both several female/male native speakers of the language.

The key to data collection is controlling for as many factors as possible so that the acoustic evidence of interest can be investigated with minimum amount of artifacts.

Quantal theory aims to elegantly describe (using physics) and organize all the acoustic features of all possible sounds into a matrix.

The reason that the set of speech sounds is finite is that while the movement of the articulators is continuous, only certain configurations tend to be articulatorily and/or acoustically stable, giving rise to fix frequencies for formants that form sounds that are relatively universal for all languages (i.e. vowels and consonants).

One non-invasive way of measuring these peaks is to use an accelerometer placed above the sternal notch (Henke) to record the acceleration of the skin during phonation.

When the velopharyngeal port opens during the production of certain sounds, such as /n/ and /m/, coupling is introduced due to the naval cavity, which gives the output a nasal quality.

The quantal theory suggests that the phonological inventory of a language is defined primarily by the acoustic characteristics of each segment, with boundaries specified by the acoustic-articulatory mapping.

While on sabbatical at KTH in Sweden in 1962, Stevens volunteered as a participant in cineradiography experiments being conducted by Sven Öhman.

[21] After returning to MIT, Stevens agreed to supervise the research of a dentistry student named Joseph S. Perkell.

Perkell's knowledge of oral anatomy permitted him to trace Stevens' X-ray films onto paper, and to publish the results.

[22] Other contributions to the study of speech production include a model by which one can predict the spectral shape of turbulent speech excitation (depending on the dimensions of the turbulent jet), and work related to the vocal fold configurations that lead to different modes of phonation.

Glottal characteristics such as vocal pitch (F0), open quotient (H1-H2), and degree of breathiness (H1-A3) can also be modeled and measured from the spectra.

[7] One of his long-time collaborators, Dennis Klatt (who wrote DECtalk while working in Stevens' lab), said that "As a leader, Ken is known for his devotion to students and his miraculous ability to run a busy laboratory while appearing to manage by a principle of benevolent anarchy.

Flanagan started graduate school at MIT in the same year as Stevens, but without a prior master's degree; he earned his M.S.

[5] On the occasion of his receipt of the Gold Medal of the Acoustical Society of America, in 1995, colleagues wrote of Stevens' Speech Group that "during its existence of almost four decades" it "has been outstanding in the support that it has provided to women researchers, many of whom have gone on to populate the upper echelons of research labs throughout the world.".

In 2004, Ken Stevens and Gunnar Fant were the joint first winners of the IEEE James L. Flanagan Speech and Audio Processing Award.