Hmm, thats interesting. Can you make a reverse engineering and lets know wat frequency, sweep maybe it is working, what does it have for speaker, how much power it is outputing, what power supply it has.

I think it must be lower at frequency of the 19-20KHz limit. Otherwise it is not possible to hear it or make you feel something or worse have a headache. May there is the secret. Make it close to the limit of human hearing point.

Ioannis