I was under the impression that these devices focused on one frequency (or maybe a small set of them) in order to leverage resonance.
For example, Wikipedia says the LRAD can use 2.5 kHz (which beyond the range of most human hearing). It can be used in other modes, including chirping and as a “public address” system, but the implication seems to be that the weapon mode is targeted at a particular frequency.
Noise canceling headphones should excel at canceling a single frequency. But I’m not sure if they response at that high of a frequency, since they’re mostly made to offset mechanical noises at the lower end of the audible range. I’m also not sure if they can offset the power put out by the sonic weapon. There’s a chance, since they are much closer to your ears and (typically) have a mostly-sealed volume of air to work with.