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What reduces the clarity of speech?

Speech clarity can be affected by many factors, both internal and external. Understanding what reduces speech clarity is important for effective communication. In the opening section, we’ll provide a quick overview of the main causes of reduced speech clarity.

Quick Answers

Some key things that can reduce speech clarity include:

  • Physical impediments in the speech production system – issues with the lungs, vocal folds, mouth, etc.
  • Hearing loss/impairment
  • Neurological disorders affecting speech and language
  • Accents and dialect differences
  • Background noise interference
  • Poor room acoustics
  • Inadequate sound systems
  • Fast rate of speech
  • Unclear diction and mumbling
  • Physical barriers obstructing speech

In the sections below, we’ll explore these factors in more detail.

Physical Impediments in the Speech Production System

Speech clarity starts with the proper physical production of speech sounds. Any structural or functional issues with the vocal tract can introduce distortions and reduce clarity. Some key physical causes include:

  • Respiratory problems – Lung conditions like chronic obstructive pulmonary disease (COPD) reduce lung capacity and airflow, leading to weak voice and imprecise consonant production.
  • Vocal fold paralysis – Paralysis of the vocal folds from nerve damage or tumors leads to incomplete closure, air leakage, and hoarse, breathy voice.
  • Vocal fold nodules/polyps – Abnormal mass lesions on the vocal folds disrupt their vibratory pattern, causing a hoarse, raspy voice.
  • Velopharyngeal insufficiency – Inadequate closure of the velopharyngeal port between the oral and nasal cavities causes hypernasal resonance and reduced oral pressure consonants.
  • Cleft palate – Structural separation in the palate allows air leakage into the nasal cavity, resulting in hypernasality and articulation errors.
  • Tongue weakness – Weakness from neurological conditions reduces tongue strength and mobility, causing imprecise consonant and vowel sounds.

Problems like these require assessment and intervention from healthcare professionals like speech-language pathologists to restore function and improve clarity.

Hearing Loss

Hearing plays a critical role in monitoring and self-monitoring speech. Hearing loss from conditions like age-related hearing loss, noise exposure, or ototoxic medications can reduce clarity in the following ways:

  • Reduced audibility of high frequency speech sounds leading to more pronunciation errors.
  • Loss of ability to monitor self-produced speech sounds and volume.
  • Increased vocal effort and loudness to compensate for hearing loss, which can distort vocal quality over time.
  • Reduced ability to adjust speech based on communication environment and listener feedback.

Hearing aids and assistive listening devices are often recommended to help improve speech clarity for those with hearing impairment. Speech therapy may also help with techniques to improve vocal quality and articulation.

Neurological Disorders

Neurological conditions affecting the speech and language centers of the brain can significantly reduce speech clarity. Some examples include:

  • Dysarthria – Weakness, slowness, or lack of coordination of the speech muscles caused by stroke, brain injury, or other neurological damage.
  • Apraxia of speech – Inability to correctly perform and sequence speech movement gestures despite intact speech muscles.
  • Aphasia – Language disorder caused by stroke or brain injury affecting the ability to comprehend and formulate language.
  • Dyslexia – Learning disability that can affect speech sound production and processing.
  • Parkinson’s disease – Progressive neurological disease leading to rigidity, uncoordinated movement, and tremors affecting speech.

These disorders require ongoing management from a speech-language pathologist. Treatment focuses on exercises and strategies to improve speech motor control, language formulation, and speech intelligibility.

Accents and Dialects

Variations in speech sounds, word pronunciation patterns, rhythm, and intonation associated with different regional and ethnic accents and dialects can present comprehension challenges for unfamiliar listeners. Key differences that may reduce clarity include:

  • Substitutions of similar speech sounds, e.g. /th/ and /d/ sounds for someone with a Japanese accent.
  • Deleted or added speech sounds in words, e.g. “impor-ant” vs “important”.
  • Different stress and intonation patterns.
  • Different speech/articulation rates.
  • Use of terminology and slang unfamiliar to the listener.

Familiarity, experience, and context help listeners adapt to accent differences. Speakers can also increase clarity by slowing rate, minimizing slang, and pronouncing carefully for unfamiliar listeners.

Background Noise

High levels of background noise mask and degrade the speech signal, making it harder for listeners to pick out the speaker’s voice. Examples of interfering noises include:

  • Environmental noises – traffic, machinery, crowds, aircraft, etc.
  • Inside building noises – air conditioning, plumbing, computer fans, printers, etc.
  • Multiple speakers talking simultaneously.
  • Reverberation and echo in large, hard-surfaced rooms.

Strategies for improving clarity with background noise include getting closer to the listener, facing the listener, speaking up without shouting, slowing speech rate, pausing more, and articulating more precisely. Noise-reduction measures and hearing assistive technologies also help.

Room Acoustics

The acoustical properties of rooms can have significant effects on speech clarity. Hard, reverberant rooms with non-absorptive surfaces cause excessive echo and reverberation, spreading and smearing the speech sounds so individual words become less distinct. Key acoustical conditions that reduce clarity include:

  • High reverberation time – sound persisting for more than 1 second.
  • Flutter echo between parallel hard surfaces.
  • Insufficient sound damping materials – curtains, carpets, acoustic tiles.
  • High ambient noise levels.
  • Distortions from room shape and size.

Professional acoustic analysis and treatments can help reduce reverberation and echo through placement of sound absorbing materials tuned to the room’s natural resonant frequencies.

Sound Systems

For lecturers, performers, and other public speakers, the sound system is crucial for delivering clear, intelligible speech to the audience. Problems like inadequate system power, loudspeaker distortions, poor microphone technique, noisy electronics, and improper tuning can degrade the audio signal and reduce clarity. Steps for optimizing clarity include:

  • Selecting adequate power and coverage for room size.
  • Choosing quality transducers – microphones and speakers.
  • Setting appropriate amplifier gains.
  • Equalizing for clear, natural sound.
  • Orienting speakers effectively.
  • Positioning mics correctly.
  • Reducing system noise and feedback.

Qualified sound technicians can properly analyze venue acoustics and design an appropriate sound system tailored for speech reproduction.

Fast Speech Rate

The speed or rate at which speech is produced significantly influences intelligibility. Faster rates reduce clarity by:

  • Blurring and slurring of consonant sounds.
  • Omitting or distorting vowels and syllables.
  • Reducing pauses between words and phrases.
  • Altering normal speech rhythm.
  • Limiting time for listener to process speech.

Slowing rate gives more distinct consonant and vowel production, better phrasing, and increased processing time for the listener. Aim for around 150 words per minute in normal conversation for optimal clarity.

Unclear Diction

Diction refers to the clarity and precision of pronouncing words. Unclear diction causes reductions, distortions, omissions, and substitutions in speech sounds that reduce intelligibility. Causes include:

  • Laziness and mumbling speech.
  • Regional dialects.
  • Habitual slurring.
  • Physical conditions limiting articulation.
  • Trying to speak too fast.

Improving diction involves conscious attention to articulating each speech sound with precision. This can be enhanced through exercises targeting problematic consonants and vowels.

Physical Barriers

Objects positioned between the speaker’s mouth and listener’s ear can physically obstruct and dampen the speech signal. Clarity is reduced when speaking through:

  • Face masks and other protective gear.
  • Windows, doors, and walls.
  • Cubicle partitions in office settings.
  • Paper, books, hands, or other objects in front of the face.

Orienting towards openings, using amplifiers, removing obstructions, and articulating precisely help overcome these barriers. Transparent face masks or face shields improve visibility of speech movements.

Summary Table

Category Factors Reducing Clarity
Physical Impediments Respiratory problems, vocal fold paralysis, nodules/polyps, velopharyngeal insufficiency, cleft palate, tongue weakness
Hearing Loss Reduced audibility, inability to monitor speech production, increased vocal effort
Neurological Disorders Dysarthria, apraxia of speech, aphasia, dyslexia, Parkinson’s disease
Accents/Dialects Sound substitutions, deletions/additions, different stress/intonation, unfamiliar terms
Background Noise Environmental, building system, multiple speakers, reverberation
Room Acoustics Excessive reverberation, flutter echo, insufficient damping
Sound Systems Inadequate power, distortions, poor tuning
Fast Speech Rate Blurring, slurring, omissions, altered rhythm, reduced processing time
Unclear Diction Mumbling, slurring, regional dialects, physical limitations, rushing speech
Physical Barriers Face masks, windows, walls, cubicles, obstructions


In summary, speech clarity can be reduced by a wide range of anatomical, physiological, acoustic, linguistic, and environmental factors. Physical impediments in the vocal system, hearing loss, neurological disorders, regional dialects, background noise, room acoustics, sound systems, fast speaking rate, unclear diction, and physical barriers can all contribute to reducing intelligibility. Careful analysis is needed to identify the contributing factors in each situation. Targeted solutions including medical intervention, hearing technologies, speech therapy, training, environmental modifications, and sound system improvements can help overcome many of these issues and restore effective communication.