For sounds below about Hz, the nerves send signals at the same frequency as the sound. For frequencies greater than about Hz, the nerves signal frequency by position. There is a structure to the cilia, and there are connections between nerve cells that perform signal processing before information is sent to the brain. Intensity information is partly indicated by the number of nerve signals and by volleys of signals. The brain processes the cochlear nerve signals to provide additional information such as source direction based on time and intensity comparisons of sounds from both ears.
Higher-level processing produces many nuances, such as music appreciation. Figure 7. The inner ear, or cochlea, is a coiled tube about 3 mm in diameter and 3 cm in length if uncoiled.
When the oval window is forced inward, as shown, a pressure wave travels through the perilymph in the direction of the arrows, stimulating nerves at the base of cilia in the organ of Corti. Hearing losses can occur because of problems in the middle or inner ear.
Conductive losses in the middle ear can be partially overcome by sending sound vibrations to the cochlea through the skull. Hearing aids for this purpose usually press against the bone behind the ear, rather than simply amplifying the sound sent into the ear canal as many hearing aids do. Damage to the nerves in the cochlea is not repairable, but amplification can partially compensate.
There is a risk that amplification will produce further damage. Another common failure in the cochlea is damage or loss of the cilia but with nerves remaining functional. Cochlear implants that stimulate the nerves directly are now available and widely accepted.
Over , implants are in use, in about equal numbers of adults and children. The cochlear implant was pioneered in Melbourne, Australia, by Graeme Clark in the s for his deaf father. The implant consists of three external components and two internal components. The external components are a microphone for picking up sound and converting it into an electrical signal, a speech processor to select certain frequencies and a transmitter to transfer the signal to the internal components through electromagnetic induction.
These electrodes in turn send the impulses directly into the brain. The electrodes basically emulate the cilia. No, the range of perceptible sound is based in the range of human hearing. Many other organisms perceive either infrasound or ultrasound. Skip to main content. Physics of Hearing. Search for:. Hearing Learning Objectives By the end of this section, you will be able to: Define hearing, pitch, loudness, timbre, note, tone, phon, ultrasound, and infrasound.
Compare loudness to frequency and intensity of a sound. Identify structures of the inner ear and explain how they relate to sound perception. Example 1. What is the intensity level in decibels of a Hz sound having a loudness of 70 phons? At what intensity level will an Hz sound have the same loudness as a Hz sound at 60 dB? Strategy for Part 1 The graph in Figure 2 should be referenced in order to solve this example.
Solution for Part 1 Identify knowns: The square grid of the graph relating phons and decibels is a plot of intensity level versus frequency—both physical quantities. Find the loudness: 75 phons. Strategy for Part 2 The graph in Figure 2 should be referenced in order to solve this example. Solution for Part 2 Identify knowns; Values are given to be Hz at 70 phons. Find the intensity level: 67 dB Strategy for Part 3 The graph in Figure 2 should be referenced in order to solve this example. Solution for Part 3 Locate the point for a Hz and 60 dB sound.
Discussion These answers, like all information extracted from Figure 2, have uncertainties of several phons or several decibels, partly due to difficulties in interpolation, but mostly related to uncertainties in the equal-loudness curves.
The Hearing Mechanism The hearing mechanism involves some interesting physics. Figure 5. The illustration shows the gross anatomy of the human ear. Check Your Understanding Are ultrasound and infrasound imperceptible to all hearing organisms? Explain your answer. Solution No, the range of perceptible sound is based in the range of human hearing.
Conceptual Questions Why can a hearing test show that your threshold of hearing is 0 dB at Hz, when Figure 3 implies that no one can hear such a frequency at less than 20 dB? If you could measure distances over the same range with a single instrument and the smallest distance you could measure was 1 mm, what would the largest be? The frequencies to which the ear responds vary by a factor of 10 3.
Suppose the speedometer on your car measured speeds differing by the same factor of 10 3 , and the greatest speed it reads is What would be the slowest nonzero speed it could read? What are the closest frequencies to Hz that an average person can clearly distinguish as being different in frequency from Hz? The sounds are not present simultaneously. Can the average person tell that a Hz sound has a different frequency than a Hz sound without playing them simultaneously?
If your radio is producing an average sound intensity level of 85 dB, what is the next lowest sound intensity level that is clearly less intense?
Can you tell that your roommate turned up the sound on the TV if its average sound intensity level goes from 70 to 73 dB? Based on the graph in Figure 2, what is the threshold of hearing in decibels for frequencies of 60, , , , and 15, Hz? Note that many AC electrical appliances produce 60 Hz, music is commonly Hz, a reference frequency is Hz, your maximum sensitivity is near Hz, and many older TVs produce a 15, Hz whine.
What sound intensity levels must sounds of frequencies 60, , and Hz have in order to have the same loudness as a dB sound of frequency Hz that is, to have a loudness of 40 phons? What is the approximate sound intensity level in decibels of a Hz tone if it has a loudness of 20 phons? If it has a loudness of 70 phons?
Suppose a person has a dB hearing loss at all frequencies. By how many factors of 10 will low-intensity sounds need to be amplified to seem normal to this person? Note that smaller amplification is appropriate for more intense sounds to avoid further hearing damage.
If a woman needs an amplification of 5. The normal human hearing range of a healthy individual is usually in-between 20Hz and Hz with the higher frequencies gradually fading during a lifetime.
Below 20Hz are called infrasounds and above Hz are called ultrasounds. Depending on your gender, age and occupation, each person's audible range may fluctuate but usually it is within those limits. Overall, the human ear is best adapted to frequencies between and Hz human speech covers the range of Hz.
Decibels dB are the unit used to measure sound intensity and anything above 90dB will cause damage to the ear. The higher the intensity of the sound the quicker it will damage the delicate structures in the ear. The main organ responsible for the hearing process is the cochlea - a small shell-like structure with tubes full of liquid and tiny, extremely sensitive hair cells.
The hair cells are integral to hearing and even the slightest damage can compromise their proper function, as they do not regenerate. This is how hearing loss develops. In terms of hearing ability, those with normal hearing should not expect or experience any loss more than 25dB. If you feel you are experiencing a loss of hearing greater than 25dB, take our free online hearing test. Results should indicate if you need to take further action to look after your hearing.
We recommend that if you have concerns, you should consult a medical professional or audiologist who can perform clinical screenings to assess hearing ability. Many animals have a wider hearing range compared to humans and pick up infrasonic and ultrasonic sounds. Sounds below 20Hz such as a heartbeat are called infrasonic and above 20kHz, ultrasonic echolocation of bats.
Dogs, for example, have a hearing range between 40 and Hz and they respond better to higher frequency sounds. That is why training whistles are designed to emit ultrasonic signals. Bats are another species whose hearing exceeds human levels and reaches to kHz. As they have limited vision, echolocation is essential for hunting and surviving. An interesting animal, the dolphin is famous for its high-frequency communication that is usually between 75 and Hz.
Below, you can see a short overview of some other animals' hearing range compared to the human range. We are one of the world's leading hearing aid specialists. HearingDirect offers a wide range of affordable products, and information resources to help improve the quality of life for the hard of hearing.
For example, here are decibel levels for some common sounds: Breathing: 10 dB Normal conversation: dB Lawnmower: 90 dB Rock concert: dB Gunshot: dB Prolonged exposure to sounds louder than 85 dB can cause damage to your hearing; sound at dB is uncomfortable and dB is the threshold of pain. When measured together, decibels and hertz tell the degree of hearing loss you have in each ear.
Degrees of hearing loss When measured together by your hearing healthcare professional, dB and Hz tell the degree of hearing loss you have in each ear.
Slight hearing loss : This is when you can't hear sounds quieter than about 15 to 20 dB, such as whispering or leaves rustling. While this is below the threshold most clinicians use to diagnose adult hearing loss, this level of hearing loss can still make listening to speech a struggle.
In children , in fact, this level of hearing loss is usually treated with hearing aids to assist in speech and language development. Moderate hearing loss : At this level, you are asking people to repeat themselves a lot during conversations—in person and on the telephone.
People with this degree of hearing loss cannot hear sounds lower than dB. Both mild and moderate hearing loss can typically be treated effectively with standard hearing aids. People with this degree of hearing loss cannot hear sound lower than dB. You may prefer using sign language to communicate. People with this degree of hearing loss cannot hear sound lower than 95 dB. How hearing loss is measured So how do you know if you have hearing loss — and to what degree?
In this case, this person cannot hear high-pitched sounds 4,, Hz range unless they are fairly loud. This will make hearing speech difficult. High-frequency hearing loss is a fairly common hearing loss pattern for people with age-related hearing loss. Others may struggle to hear low-frequency sounds and other sound ranges. Nov 8. Nov 4. Nov 2. Nov 1. Find a clinic.
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