Mother's Under-$30 Hearing Aid

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

Sound Loudness and Hearing Loss

Hearing loss can be brought on by many different things, but the most common cause is repeated exposure to high-intensity sounds. Sound levels are measured in units called decibels (db), and human hearing spans a range of about 140 db. (To put these numbers in perspective, a whisper at five feet is 0 db, a jackhammer at two feet is about 90 db, jet aircraft noise can be as high as 120 db, and disco music often exceeds 130 db.)

Sensorineural damage begins at about 85 db. Constant—-or even periodic—exposure to sound above this level harms the hair cells of the inner ear and thus causes hearing loss. The disease is progressive (the degree of degeneration is proportional to the length of exposure) and more or less irreversible.

It's interesting to note that though we have a very limited dynamic range at low frequenciesmost of us can't hear any sound below 40 Hz-the destructive power of such frequencies is great. Many discos were famous, at one time, for bodyvibrating sounds that emanated from subwoofer speakers mounted below the floor-unheard sounds that exceeded 130 db and were thus capable of causing permanent hearing damage. In most cases, however, we can physically feel sound vibrations when they reach 125 db, and 130 db sound is actually painful.

Doctors warn those who must work around high-intensity noises to take precautions to preserve their hearing by wearing protective devices such as earplugs or ear covers.

Figure 1 The Effects of Sound Intensity and Frequency on Hearing Perception
Figure 2 Hearing Aid Schematic
Parts List
Parts Layout

RSS | Comments | E-mail | Print