The “speech banana” is a concept audiologists use to visually represent the range of sounds found in human speech on a hearing test chart. This area highlights the specific frequencies and loudness levels that make up the phonemes, or individual speech sounds, we use to communicate. It allows clinicians and patients to visualize how much of their hearing ability is dedicated to understanding spoken language. By plotting a person’s hearing ability against this area, audiologists can quickly determine which parts of conversation may be difficult to perceive.
Understanding the Hearing Chart
The speech banana is an overlay plotted onto an audiogram, which is the standard graph used to chart a person’s hearing sensitivity. This graph uses two primary axes to define the properties of sound. The horizontal axis, or X-axis, represents frequency, which is what we perceive as pitch, and is measured in Hertz (Hz).
The frequency scale begins with lower pitches, such as a deep voice or a bass note, on the left side, and increases toward higher pitches, like a whistle or a bird chirping, on the right side. The vertical axis, or Y-axis, represents intensity, which is perceived as loudness, and is measured in decibels (dB).
Intensity is plotted from the softest sounds at the top of the chart, typically starting around zero or negative decibels, down toward the loudest sounds near the bottom. During a hearing test, the softest sound level a person can detect at each frequency is marked on this chart, creating a unique line known as the hearing threshold.
Mapping the Sounds of Human Speech
When speech sounds are plotted onto the audiogram, they cluster together to form the speech banana shape. This area generally spans a frequency range from approximately 250 Hertz up to 4000 Hertz and covers an intensity range of roughly 20 dB to 60 dB. This specific concentration includes nearly all the phonemes of the English language.
Within the speech banana, the different sound elements of speech are mapped according to their physical properties. Vowel sounds, such as ‘a,’ ‘o,’ or ‘u,’ are concentrated toward the lower frequency, louder side of the banana. These sounds carry the majority of the acoustic power and volume in speech.
Conversely, consonant sounds, like ‘s,’ ‘f,’ ‘th,’ or ‘sh,’ are grouped toward the higher frequency, softer side of the shape. Although quieter, these consonants are responsible for speech clarity. They allow listeners to distinguish between similar-sounding words, such as “sat” and “fat.”
How Hearing Loss Affects Communication
The speech banana is used diagnostically when compared against an individual’s hearing threshold line plotted on the audiogram. If the person’s threshold line falls below any part of the speech banana, it indicates that they cannot hear those specific speech sounds without amplification.
Age-related or noise-induced hearing loss frequently affects the higher frequencies first, causing the threshold line to drop sharply on the right side of the chart. This means the person can hear the loud, low-frequency vowel sounds, but they miss the softer, high-frequency consonants. Consequently, speech sounds muffled or indistinct because the listener lacks the acoustic information needed to process the words clearly.
Interventions such as hearing aids or cochlear implants are designed with the speech banana in mind. An audiologist programs these devices to amplify the speech sounds that fall below the person’s threshold line. This programming effectively raises the volume of the previously unheard sounds, pushing them above the threshold line and back into the audible range. Restoring access to the full spectrum of phonemes within the speech banana improves a person’s ability to hear and understand everyday communication.