Room formants of this nature reinforce themselves by emphasizing specific frequencies and absorbing others, as exploited, for example, by Alvin Lucier in his piece I Am Sitting in a Room.
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(Incidentally, Alexander Graham Bell's father, Alexander Melville Bell, was a phonetician.) During World War II, work at the Bell Telephone Laboratories (which invented the spectrograph) greatly facilitated the systematic study of the spectral properties of periodic and aperiodic speech sounds, vocal tract resonances and vowel formants, voice quality, prosody, etc.
It is, however, most likely that neither the German animator Lotte Reiniger nor the American puppeteer Tony Sarg knew of his work, and it was Reiniger who first established many of what are now the standard practices of the formant with her first film, Das Ornament des verliebten Herzens (The Ornament of the Enamoured Heart, 1919).
As with any fluid-filled tube, resonances (called formants) change as the vocal organs such as the tongue and velum move.