Final answer:
A capacitor should be placed in parallel with the hearing aid's speaker to adjust the output for presbycusis, a hearing loss that affects higher frequencies.
Step-by-step explanation:
To adjust the output of a hearing aid amplifier for presbycusis, a capacitor should be placed in parallel with the hearing aid's speaker.
Presbycusis is a hearing loss that affects higher frequencies, so to compensate for this, the capacitor in parallel with the speaker will act as a high-pass filter, allowing the higher frequencies to pass more easily and be amplified.
The parallel capacitor will allow the lower frequencies to bypass the speaker and reduce their amplification, focusing more on amplifying the higher frequencies affected by presbycusis.