Even during times of near total silence, we will almost always experience some amount of background noise. How well we hear it, and how distracting it may be, depends on its frequency and intensity, as well as our individual hearing ability.
Sound is a type of energy comprised of vibrations that travel through a transmission medium such as gas, liquids, or solids. These vibrations move in waves creating compressions and refractions. Once these waves reach the ear, the vibrations create movement through the eardrum allowing us to hear these vibrations as sounds.
What is ‘Intensity’ in Audiometric Testing?
We often turn up the volume to hear our favorite song on the radio more clearly, to drown out the background noise when watching television, or to draw focus to the things we really want to hear. But turning up the volume isn’t always the ideal solution, and can actually be a key identifying factor in determining hearing loss.
Volume – also known as intensity- are the levels at which sounds can be heard. When performing a hearing test, clinicians – including audiologists, hearing instrument specialist, and hearing technicians, use different levels of intensity for specific sounds that are then presented one ear at a time to the client.
How is it Used?
Intensity is used in audiometric testing to understand the volume level at which a specific frequency can be heard by the client. It is measured in decibels (dB) distributed at different increments throughout the testing process. The range of human hearing is typically between -10dB and 120dB. Presentation levels are determined by the audiologist starting at a clearly audible level and lowering using a bracketing technique until the softest level at a particular frequency is identified.
As far as loudness – or intensity – is concerned, humans can generally start to hear at -10dB. The average human conversation registers at roughly 60dB. But once sound levels (loudness) start to reach 85dB, they can be considered dangerous to long-term hearing, especially if an individual is exposed for prolonged periods of time.
What is ‘Frequency’ in Audiometric Testing?
We’ve all seen the dog who comes running to his master after a whistle is blown that none of us could here. That’s because the frequency of a dog whistle can be undetectable to the average human ear. Frequency, also known as pitch, is used in conjunction with different intensity levels to help determine hearing abilities.
Typically sounds characterized as ‘low frequency’ are considered to be deep noises – think low rumbling thunder or the sound of a tuba — and ‘high frequency’ sounds (a squeak, squeal, or a child’s voice) have a high pitch.
The pitch of a frequency is determined by the length of the sound wave. The shorter the wave length, the higher the frequency pitch.
How is ‘Frequency’ Used?
Frequency, measured in Hertz (Hz), is used to establish the levels of intensity of specific tones that can be heard by the patient. It is commonly stated that a healthy young person can hear frequency ranging from 20Hz to 20kHz. Audiometric testing is generally performed at 250-8000Hz since this range represents the human speech spectrum.
Everyone is unique in their ability to hear different frequencies at different intensities. There are a number of factors that play into this differentiation including age, overall health, profession, past noise exposures, and daily routines. Using this information, clinicians are able to clearly pinpoint specific types of hearing loss, and make recommendations for treatment and the healthy maintenance of hearing levels.
Reading an Audiogram
Audiology utilizes a number of unique tools in order to accurately read and interpret the overall status of a patient’s hearing ability. Audiometers, including SHOEBOX Audiometry, work by presenting a series of tones at varying frequencies and intensity levels. The patient is then expected to identify when they hear those tones, even if they are barely perceivable. The results are recorded as an audiogram which provides a graphical representation of the hearing test results.
Audiograms use a grid pattern with a vertical and horizontal axis. Located on the axes are the intensity (y-axis) and frequency (x-axis) levels. When the softest level of a particular tone that the client is able to perceive is identified (also known as a threshold), a data point will be inserted onto the graph, displaying the results.
Each ear is displayed using unique symbols in order to properly distinguish results. Specific symbols, often presented in red, are used to display the results for the right ear. Another set of symbols, often presented in blue, are used to represent the left ear. In interpreting the various symbol sets, clinicians are able to determine the exact levels of the client’s hearing and qualify the type of hearing loss which determines potential next steps.
Many factors influence whether or not an individual is able to hear different sounds. We hope you have learned a thing or two about some of the key aspects of human hearing. The more we know, the more we can protect this wonderful sense that helps so many of us effectively communicate and enjoy the magical sounds of life.
Written by: Trevor Griffith