The Presences, because the greater part of their bulk is far underground, undoubtedly store energy from earth movement. It is not mentioned that there are any Jubal-quakes. Could the Presences be surface extensions of large or small tectonic plates, storing vast quantities of potentially destructive energy rather than using it up in earthquakes and vulcanism?
The Enigma, the "Mad One," is described as being twinned, two tines of a monstrous fork. Some crystals grow as "twins," that is, as mirror images of one another, and the plane between them is called the "twin boundary." Dislocations cannot move across surfaces, and so cannot be transmitted from one crystal to another unless they are in contact. Even when in contact the transmission of dislocations would be very poor unless certain geometric considerations are met. Thus, the Black Tower could presumably speak to the Jammers without sharing their minds. However, dislocation transmission or movement does occur across the twin boundary, and we can imagine the Enigma as a being that is actually of two minds, with each of these minds interfering with or perturbing the other.
As for the Tripsingers, what is it they do? Each Frank-Reed source has a frequency at which it vibrates, its own harmonic frequency, which may be multiple. If one were to bombard a Frank-Reed source with any other frequency, it could generate more dislocations, that is, the Frank-Reed source will operate. However, the Frank-Reed source would be absolutely transparent to its natural frequency.
If the Tripsingers simply sang in accord with the natural frequencies that were the "mind," conscious or unconscious, of the Presences, they would leave no information behind them, that is, they would not wake the Presences up. If certain sounds were "alertive," wagon wheels for example, then it would have been the Tripsinger's job to produce complementary sounds, which, when superimposed on the wagon wheels, yielded exactly those frequencies that were transparent to the Presences. This was, obviously, quite complicated enough.
A subject of some interest might be whether talking to them when they were awake would be an easier or a more complicated matter.
Tepper,Sheri - After Long Silence Page 39