Audiograms & Sound Levels
A completed audiogram will show the results of a hearing test. A chart similar to the one below will show the level of hearing for each ear. The vertical axis will depict the level of hearing in decibels. Soft sounds (-10 to 0 dB) at the top with loud sounds (110 dB) at the bottom. Normal hearing can hear zero decibels 50% of the time. Normal conversation is usually in the 55 dB range. The horizontal axis indicates the frequency range and the ability to hear across frequencies of 125 Hz (a very low tone), to 8,000 Hz (a very high tone). An audiogram will show which ear has the best hearing, your level of hearing loss and your best hearing frequency range.
Audiogram Sample
|
Noise Induced Hearing Loss
(NIHL), can be caused in two ways, a single loud sound or repeated exposure to loud sounds over a period of time. Long term exposure to noise over 90 decibels (dB) can cause gradual hearing loss. Regular exposure of 110 decibels or higher for more than one minutes can lead to permanent hearing loss. You should not expose yourself to more than 15 minutes of unprotected exposure to 100 dB's.
The following table helps to relate various sounds to decibel (dB) levels.
| Common Sounds |
Decibels (dB) |
Hearing Sensation |
| Threshold of hearing |
0 |
Hearing begins |
| Rustling leaves |
10 |
Just audible |
Quiet whisper at a distance
library, very quiet PC |
20-30 |
Very quiet |
Quiet office, normal PC,
bedroom, sound of a mosquito
refrigerator hum |
35-40 |
Subdued sound |
Light auto traffic (100 feet),
normal conversation |
50 |
Clearly audible |
Restaurant, air-conditioning,
slightly elevated conversation |
60 |
Slightly intrusive |
Noisy restaurant, freeway
traffic, busy office |
70 |
Noisy, hard to use a phone |
Vacuum cleaner, alarm clock,
hair dryer |
80 |
Very noisy, annoying |
Heavy traffic, subway,
garbage truck, lawnmower |
90-100 |
Very loud |
Rock concert, piledriver,
chainsaw, snowmobile |
110-120 |
Extremely loud |
Jet take-off, thunderclap,
jackhammer, auto horn (3 feet) |
120-130 |
Almost intolerable |
Air raid siren, jet take-off
at close range (100 feet) |
140 |
Painfully Loud, Pain threshold |
Rocket launch pad with
no ear protection |
180 |
Instant eardrum perforation |
A reversible hearing loss condition, also called temporary threshold shift can be caused by certain noises such as firecrackers or a loud gunshot. This condition is called
tinnitus
where the symptom is a ringing in the ears. Non-occupational noise can also be a source of premature hearing reduction. Listening to a portable CD player at 70% volume for 1 hour has been shown to be equivalent to the peak recommended noise by government for occupational exposure.
|
