Hearing thresholds are clinically tested at octave-spaced frequencies covering the speech range

Evidence

For pure sine waves, however, the sensitivity to change is markedly different and is a strong function of both amplitude and frequency. For example, at 1 kHz, the just-noticeable amplitude change varies from 3 dB at 10 dB(SPL) to 0.3 dB at 80 dB(SPL). — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 648 (#expands, via linked claim)

Categorization

• corroborated: 2 independent passages support this claim
• XREF: connects to: Standards accept up to 25 dB of hearing loss as medically normal; Normal hearing is operationally defined as a four-frequency average threshold below 25 dB HL. — Dijk, Pim van, Physiology, Psychoacoustics and…, 4163; Envelope-following response measures capture hearing aspects beyond the audiometric threshold — Dijk, Pim van, Physiology, Psychoacoustics and…, 5885 (+5 more)

Broader Connections

• Auditory sensitivity varies nonuniformly across the frequency range #expands (0.80) — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 648