Before we can understand hearing loss, we must first understand what hearing entails. When we hear sounds, we really are interpreting patterns of movement of air molecules. We can describe sounds in terms of their frequency (or pitch) and intensity (or loudness). Frequency is measured in hertz (Hz). A person who has hearing within the normal range, can hear sounds that have frequencies between 20 and 20,000 Hz. The most important sounds we hear every day are in the 250 to 6,000 Hz range. Speech includes a mix of low and high frequency sounds. Vowel sounds like "u" have low frequencies (250 to 1,000 Hz) and are usually easier to hear. Consonants like "s," "h," and "f" have higher frequencies (1,500 to 6,000 Hz) and are harder to hear. Consonants convey most of the meaning of what we say. Someone who cannot hear high-frequency sounds will have a hard time understanding speech.
Intensity, or loudness, is measured in decibels (dB). A person with hearing within the normal range can hear sounds ranging from 0 to 140 dB. A whisper is around 30 dB. Conversations are usually 45 to 50 dB. Sounds that are louder than 90 dB can be uncomfortable to hear. A loud rock concert might be as loud as 110 dB. Sounds that are 120 dB or louder can be painful and can result in temporary or permanent hearing loss.
Impairments in hearing can happen in either frequency or intensity, or both. Hearing loss severity is based on how well a person can hear the frequencies or intensities most often associated with speech. Severity can be described as mild, moderate, severe, or profound. The term "deaf" is sometimes used to describe someone who has an approximately 90 dB or greater hearing loss or who cannot use hearing to process speech and language information, even with the use of hearing aids. The term "hard of hearing" is sometimes used to describe people who have a less severe hearing loss than deafness.
Hearing loss can affect one or both ears. A loss that affects one ear is called a unilateral loss. A loss that affects both ears is called a bilateral loss.
There are four main types of hearing loss:
Approximately 30% of children who are deaf or hard of hearing also have one or more other developmental disabilities, such as mental retardation, cerebral palsy, vision impairment, or epilepsy. [Read more about developmental disabilities]
Hearing loss can affect a child's ability to learn both to speak and to understand spoken language. This is especially true if the child is born with a hearing loss or loses his or her hearing before 2 years of age. People with hearing loss may communicate using speech (sometimes called oral communication), sign language (sometimes called manual communication), or a combination of both. Oral communication focuses on speech, listening with hearing aids, and sometimes lipreading. Manual communication includes sign language.