A patient of mine just told me about a website that explains the audio spectrum, audio production, microphones, sound waves, sound perception, and more: Teach Me Audio: No nonsense guide to Audio Production. Speech is between 250 and 8000 Hz, so those are the frequencies that get tested in an audiogram. (Actually, sometimes I test higher than that if someone is starting chemotherapy. Chemo is ototoxic and the toxicity shows up first in the ultra high frequencies. So I test above 8kHz before and at intervals after chemo. If hearing drops above 8 kHz, the oncologist knows chemo has reached ototoxic levels and they may choose to tweak the dosage a bit.)
While the whole website is fascinating, the Audio Spectrum page can help you check your hearing aids. If you can’t hear part of the frequency range between 250 and 8000 Hz when you’re wearing your hearing aids, they may need to be reprogrammed.