Exposure to 90 db AND 4000 Hz noise results in –
**Core Concept**
Exposure to high-intensity noise, specifically above 85 dB, can cause noise-induced hearing loss (NIHL), a form of sensorineural hearing loss. The threshold for NIHL is often cited as 85 dB, but the risk increases significantly above 90 dB, especially at frequencies between 2,000-4,000 Hz.
**Why the Correct Answer is Right**
Noise-induced hearing loss at 90 dB and 4,000 Hz is due to the mechanical damage to the hair cells in the cochlea, specifically the outer hair cells, which are responsible for sound amplification. The 4,000 Hz frequency is particularly susceptible to damage due to its high energy density and the mechanical properties of the cochlea. Prolonged exposure to this frequency and intensity can lead to permanent damage and hearing loss.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a particular frequency or intensity, making it too vague to be correct.
**Option B:** This option is incorrect because it does not account for the specific frequency of 4,000 Hz, which is a critical factor in NIHL.
**Option C:** This option is incorrect because it does not specify a particular intensity, which is a crucial factor in determining the risk of NIHL.
**Clinical Pearl / High-Yield Fact**
The "4 kHz notch" is a common audiometric finding in individuals with NIHL, where there is a noticeable dip in hearing sensitivity at 4,000 Hz.
**Correct Answer:** C.