Children of Orion
Sonic damage is occurred by using sub sonic or ultra sonic vibrations to cause damage to soft tissue.
This form of damage needs a medium such as air to travel through. This damage form may be refered to as a Disruptor, Phasor, or other types of jargon which refers to the molecular level of vibration to cause damage. Large Sonic canons can be devastating to not only troops but also rigid structures.
To mitigate this type of damage the only truly effective way is a harmonic screen. This force screen will detect the frequency of the Sonic disruptor wave and generate a complementary wave form to cancel out the in coming sound wave.