William had significant hearing loss of higher tones. In fact when he was tested, the audiologist said he wasn't hearing some tones at all - I think it's consonants are higher tones than vowels. That's why elderly people often hear you speaking, but misunderstand what you said. The brain fills in the sounds they didn't hear, apparently! So, if you say "cat" they could hear hat, mat, rat, pat - whatever, take your pick! They won't hear some telephones, no matter how loud, because the tone is too high. As I was talking to the audiologist, the window was open and there were birds singing in the trees right outside. The audiologist remarked on it, because it was quite loud, and said "your husband can't hear that at all. He will not have been able to hear birds singing for a number of years."
This type of hearing loss leads to particular difficulty with hearing women's voices. I learned to deepen my tone and speak more slowly for William, to the extent that my voice is permanently a bit deeper than it used to be. Speaking louder won't help - the person can hear lower tones perfectly, so speaking louder will make lower tones too loud, and they still won't hear the higher tones! Good, digital hearing aids can be calibrated to compensate somewhat, but with dementia in the mix, it's really difficult. William got a hearing aid, but he couldn't cope with it at all. He wore it maybe twice, and wouldn't tolerate it after that.
