manometric capsule

manometric capsule

[‚man·ə¦me·trik ′kap·səl]
(acoustics)
A device for studying air vibrations in a pipe or resonator, consisting of a rubber membrane which is stretched over a hole in the pipe, or over the end of a flange attached to such a hole, and apparatus for measuring vibrations of the membrane.
References in classic literature ?
He had not been forgetful of "Visible Speech" all this while, but had been making experiments with two remarkable machines--the phonautograph and the manometric capsule, by means of which the vibrations of sound were made plainly visible.