An audiogram is a graph that records the way a person responds to specific sounds called pure tones. The audiologist measures hearing threshold at the pure tone of each frequency. Hearing threshold is the intensity at which a pure tone is barely detected 50 percent of the time.
Various frequencies or pitches are measured to determine how you hear at each area of the hearing organ. During a hearing test, the frequencies used in speech and in common everyday sounds are tested. When frequency is plotted on the graph, low pitches are on the left side on the vertical lines progressing to the highest frequencies on the right side of the graph. An audiogram is similar to the design of a piano – low pitches to the left, higher pitches to the right.
Intensity is measured to determine how loud a frequency needs to be heard. A decibel (dB) is a measurement of sound loudness (sound power) and grows more rapidly than a linear measurement. For example, 20 feet is 20 times longer than one foot but 20 decibels is 100 times more powerful than one decibel. When intensity is measured, it is plotted on the audiogram on a horizontal line. The lower the mark (the larger the number) on the graph, the more sound power is needed to hear it.
Earphones or insert earphones are used to test hearing as it passes through the outer, middle and inner ear. Sound heard through an earphone is called the air conduction response giving you the degree of hearing loss. To determine the type of hearing loss you have, a bone conduction oscillator is placed on the mastoid bone behind your ear. The bone oscillator bypasses the outer ear and middle ear and gives a direct response of the hearing organ at each frequency. This is called the bone conduction response. The air conduction and bone conduction responses are plotted on the audiogram.
Degrees of Hearing Loss
0 dB – 20 dB normal hearing
20 dB – 40 dB mild loss
40 dB – 50 dB moderate loss
55 dB – 70dB moderately severe
70 dB – 90 dB severe loss
>90 dB profound loss
Types of Hearing Loss
Sensorineural loss – the hearing organ is impaired.
Conductive loss – the outer or middle ear has impairment. The hearing organ is normal.
Mixed loss– both conductive and sensorineural impairment.
Conductive Hearing Loss
Hearing loss that is the result of blockage, damage, or disease to the outer and/or middle ear is called a conductive loss. The conductive mechanism consists of the outer ear, ear canal, eardrum, eustachian tube and middle ear bones. Conductive hearing loss means there is a difference between bone conduction responses of the hearing organ and air conduction responses. Typical causes of this type of loss are ear infection, otosclerosis, ruptured eardrum, and wax in the ear canal.
Sensorineural Hearing Loss
Hearing loss because of dysfunction in the hearing organ or in the hearing pathways in the brain is called sensorineural. This type of loss has the same response of intensity for air and bone conduction. Typical causes of this type of loss are noise exposure, side effects of medication, heredity and viruses.
Mixed hearing loss
Hearing loss that has both conductive and sensorineural causes is known as a mixed hearing loss. This type of loss has some dysfunction in the hearing organ and some dysfunction in the mechanical area of the hearing mechanism. Typical causes for this type of hearing loss are nerve damage, wax build up in the ear canal after you already have a hearing loss, otosclerosis, ear surgery, heredity and trauma.
As you can see, hearing loss is complicated to understand and manage. Don’t trust your hearing and ability to interact with others simply to the lowest bidder. Because hearing is different at each frequency, it is not simply a matter of making sound louder. Each frequency must be modified independent of the next, so that you can hear as comfortably and naturally as possible. Find an audiologist who will give you time to discuss your needs and be willing to research the best possible solution for you. FBN
Karon Lynn is a doctor of audiology and practices at Trinity Hearing Center. She has 30 years of experience working with hearing impaired individuals. Dr. Lynn may be reached at 928-522-0500, or by email at firstname.lastname@example.org.