This post is closely related to the post on using the register key, the post on bass clarinet underblown multiphonics and also to the post on Eb clarinet dyads. It might be worth reading those, as well as the posts on spectral multiphonics for Bb, bass and contrabass clarinets, and Bb and Bass dyads to have a complete overview of this aspect of clarinet playing.
It surprised me that actually these underblown multiphonics are easier to achieve on the Eb clarinet than on the Bb. Descending from a C above the staff, I can achieve the underblown effect all the way down to the written B, and I can normally only manage to get as far as a D with the Bb clarinet.
As usual these are in written (transposed) pitches. The fingering for each multiphonic is actually the same as the fingering for the top note, so you can notate these by just writing u.b. or underblow. If you’re worried about confusing the clarinetist, include a link to this page in your legend.
As with the Bb and bass clarinet equivalents of this technique, these are best performed at quiet dynamics.
Going upwards from the C sharp, the multiphonics are quite fragile, but still very effective.
There’s also a slightly different set of lower pitches available with alternative fingering choices for the first three notes in the second series: