There are two other ways in which I’ve seen hearing impairment approached in the field.
Pen and pencil can be highly effective. Getting someone with good handwriting to scribble things down can work well. Similarly, I’ve known of departments to hire an audio tour guide system like you would get in a museum. Everyone was given one of those small portable systems and the presenter had a little microphone. This ensured everyone could hear, regardless of whether they had an impairment or not. One thing I liked about this latter approach was that everyone had the same equipment which meant that certain individuals are not feeling excluded or seen to be given ‘special’ treatment. It avoids making assumption and considers the social dimension of inclusivity.