sensorineural hearing loss typically begins in high-frequency hair cells
In presbycusis, most old people cannot hear the high-frequency sounds, because of some loss of hair cells in their cochlea. unlike some other vertebrates like fishes and reptiles, these hair cells can be re-generated. However, in Humans, they cannot be.
As a result of these sounds that have higher pitches such as the buzzing of a mosquito, are muffled to them. Therefore, talking in a frequency is necessary, as this will aid the old people hear the medical technicians better.