My neighbor has a deer repeller that emits a high frequency sound that is supposed to be inaudible to humans, however I hear it and it is painful.

They beep loud and constant humans can hear it

In some cases it is. depends on the tick. and if it's for humans or animals. Best get a known repellent for humans

yes it can cause a stroke to ferrets

How are you measuring the output -- the human ear cannot hear sound in the range of "ultrasonic" vibrations.

You will not get more distortion, in fact possibly a little less because the newer speakers have a higher power rating and can thus handle more power without cone breakup.
However - you indicate the the higher powered speakers have an inferior frequency response with the high end reduced from 20kHz to 16kHz - which is very surprising. This will mean that while not being any more distorted, the system will sound just a little less crisp and sharp at the high frequency end of the spectrum. Mind you, most adults over 25 - 30 years or so have impaired hearing above about 15 kHz, so chances are the difference in sound will be completely inaudible to many listeners :o)

is the range electric? if you have an electric stove your dog may be hearing high frequencies that are inaudible to humans. If it is a gas stove it could still be making high pitch sounds as the gas flows through small pilot holes to stove top. If it is electric there is not much you can do besides not using it or getting another. on a gas stove you could try increasing or decreasing the amount of gas flow from the valve on wall. or have a service tech take a look for you.

Bell collars are probably uncomfortable on most dogs becauseof the high pitch sound they can emit. Dogs can hear sounds at very high frequencies that humans cannot hear. So a bell around your dog's collar may be makingan unpleasant noise for him that you aren't even aware of.

My understanding is that various hair cells in the cochlea resonate when excited by certain frequencies of sound. So that in a sense, your ear is a complex vocoder of sorts. I don't know all that much about the physiology of sound, but there are many interesting ecological aspects (see works by A. Bregman).

If you've studied differential equations or electrical circuits, then you'll know thatphysical systems have an associated frequency response (they only respond to certain frequencies or frequency ranges). I'm not sure how much is physical response, and how much the brain filters out. If humans could hear to 0 Hz, though, for example, we would be bombarded by useless low frequency noises all around us. From an evolutionary standpoint, 20Hz-20kHz, seems to cover most of the useful noises to survive, communicate, and procreate.

if it sounds garbled it may be due to digital communication. most scanners cannot recieve the digital communication. that is why you hear a garbled inaudible sound from it.