by Neil Bauman, Ph.D.
A hard of hearing person asked:
Is the noise damage threshold the same for me as it is for a person with normal hearing? Do I just add my decibel loss (by frequency) to the noise damage threshold for normal ears? [approximately 80 to 85 dB] If sustained noise at 90 dB is bad for a person with normal hearing, does my noise damage threshold start at 150 dB because I have a 60 dB hearing loss?
Excellent question. I used to wonder about this too. It sounds so plausible on the surface–hard of hearing people can stand far more noise than hearing people because of their underlying hearing loss.
Although this is generally true for people with conductive hearing losses, it certainly is not true for the vast majority of us since we have sensorineural hearing losses.
Here is why. Think about this logically. The mechanism of damage is the same whether we have normal hearing or are hard of hearing. Excessively loud sounds damage our ears by destroying both the minute hairs (cilia) on the hair cells, and the underlying hair cells themselves too. When this happens, that hair cell no longer sends a signal to our brains. As a result we end up with a hearing loss at the frequency of sound that hair cell was sensitive to.
At first, if we have normal hearing, the few destroyed hair cells would not produce noticeable hearing loss. But when enough hair cells are destroyed, the message being sent to our brains is riddled with “gaps” which we notice as hearing loss. The actual damage to our inner ears is the same whether we have near normal hearing or have a profound hearing loss.
However, if we have a severe or profound loss, we may not seem to lose much more hearing from being exposed to loud sounds. This is not because we have a higher tolerance for loud sounds, but because there are not many hair cells left to be destroyed! (I’ve seen pictures where whole banks of hair cells are completely missing. This is quite striking when compared to pictures with all the hair cells present.)
Therefore, in answer to your question, “No, you cannot add the amount of your hearing loss to the noise damage threshold to find the amount of noise you can stand without further damaging your hearing.” For example, it is absolutely wrong for me to think that since I have an 80 dB loss, I can stand noise at 90 dB plus the 80 dB I am missing for a total of 170 dB before I do any further damage to my ears. This loud a sound will definitely instantly destroy more of my remaining hearing.
Not only that, in actual fact, I will be writhing in pain long before I hear a sound that loud. Why? Most of us with severe or worse hearing losses usually have severe recruitment as well. As a result, our tolerance for loud sounds is actually much less than for those with normal hearing. A sound of 110 dB, while very loud to a person with normal hearing will actually cause us pain because we perceive it an too loud to stand!