The labyrinth in the inner ear consists of the bony and membranous parts and comprises the cochlea, vestibule, and semicircular canals. It serves both sound transduction (cochlea) and balance perception (vestibular organ). The spaces filled with endolymph transmit mechanical stimuli to hair cells, which convert them into electrical signals. Diseases such as labyrinthitis or Meniere's disease lead to dizziness, nausea, and hearing loss. Imaging techniques and functional tests (caloric, VEMP) examine the integrity of the labyrinth.

Labyrinthitis is an inflammation of the inner ear, typically caused by a virus or bacteria, and affects both the hearing and balance organs. Symptoms include acute vertigo, nausea, vomiting, and often unilateral hearing loss or tinnitus. Diagnosis includes audiometry, vestibular function tests, and, if necessary, MRI to rule out other causes. Treatment combines antiviral or antibiotic medications with corticosteroids and vestibular rehabilitation training. In most cases, vestibular function recovers partially, but residual damage can leave persistent dizziness or hearing loss.

Noise pollution refers to exposure to harmful or disturbing sound levels in the environment and at work. It is measured in dB A and weighted over time (e.g., LEX,8h). Chronic noise pollution leads to stress, sleep disorders, and work-related hearing loss. National and international guidelines set limits for industrial, traffic, and recreational noise. Preventive measures include noise barriers, hearing protection, and quiet zones in cities.

A noise indicator is a key figure that quantifies noise pollution, e.g., Lden (day-evening-night), Lnight, or Lday. It integrates noise levels and time proportions to assess health risks. Municipal noise maps use indicators to identify areas of high pollution and plan protective measures. Specific indicators such as LEX,8h apply to workplaces. Indicators form the basis for noise action plans and environmental reporting.

A sound level meter is a measuring device that records sound pressure levels in real time and evaluates them in dB. Professional Class 1 and Class 2 meters comply with standards (IEC 61672) for precision and frequency weighting (A, C filters). They are used in occupational safety, environmental monitoring, and room acoustics. Calibration with external calibrators ensures measurement accuracy. Mobile versions and apps offer simple indicators, but do not achieve laboratory quality.

Noise protection includes technical, structural, and organizational measures to dampen sound sources or minimize sound propagation. Examples include noise barriers, absorbent materials, and traffic calming measures. Personal hearing protection (earplugs, earmuffs) supplements structural protection. Standards regulate minimum requirements for sound insulation in buildings. Effective noise protection improves the quality of living and working and prevents hearing damage.

Noise protection regulations are legal frameworks at national or EU level that set limits and procedures for noise monitoring. They define permissible levels in industrial, traffic, and residential areas, as well as night and day times. Residents can file noise complaints and enforce measures such as speed limits or noise barriers. Local authorities draw up noise action plans based on regulations. Violations are punished with fines.

Noise-induced hearing loss is an occupational disease caused by chronic exposure to noise, leading to sensorineural hearing loss, particularly in the high-frequency range. It manifests itself as "crackling" and a declining audiogram curve from 3 kHz onwards. Prevention through hearing protection and regular preventive audiometry is required by law. Treatment involves hearing aids that specifically compensate for high-frequency loss. Rehabilitation includes auditory training and workplace adjustments.

Noise prevention aims to minimize noise pollution before it causes damage to health. It includes risk assessment, planning protective measures, and informing those affected. Technical prevention measures include quieter machines, structural insulation, and traffic control. Personal prevention measures include hearing protection and rules of conduct. Monitoring and regular measurements ensure the effectiveness of the measures.

Auditory latency is the time between a sound stimulus and a measurable response in the auditory system, e.g., evoked potentials or conscious perception. Latency times provide information about the functional status of peripheral and central auditory pathways. Prolonged latencies indicate demyelination, tumors, or neuropathic damage. In hearing aids, signal processing latency is minimized to ensure audio-video synchrony. Standard values exist for ABR, MLR, and CAEP components.

Lateral inhibition is a neural principle whereby activated neurons inhibit their neighbors to increase contrast and edge sharpness. In the auditory system, it improves frequency selectivity by attenuating adjacent frequency channels. This results in clearer sound and speech comprehension, especially in complex sound environments. Disruptions in lateral inhibition can cause broader sound fields and poorer discrimination. Models of this effect are incorporated into hearing aid filter designs.

Laterization refers to the apparent perception that a sound source is located to the left or right of the center of the body, based on interaural time differences (ITD) and level differences (ILD). The brain compares minimal differences in travel time and volume between both ears to determine direction. Laterization is essential for spatial hearing and situational orientation, for example in traffic. When fitting hearing aids, it is important to ensure that binaural synchronization is maintained so as not to distort laterization. Tests in the sound field measure laterization accuracy and help to identify processing disorders.

Loudness is the subjective auditory perception of the intensity of a sound, which does not correlate linearly with sound pressure (dB SPL). Psychoacoustic models such as the Zwicker model describe how frequency and level together determine the perceived loudness in sone. Loudness scales (see below) standardize this perception for technical applications and hearing aid fitting. Loudness depends on context, duration, and frequency spectrum; different loudness levels can be perceived at the same level. Hearing aid compression optimizes loudness perception by amplifying soft sounds and attenuating loud ones.

In loudness scaling, test subjects subjectively rate the perceived loudness of test signals on a numerical or verbal scale. Methods such as category scaling or magnitude estimation provide functions that convert sound pressure into loudness (sone). These functions are used to calibrate hearing aids to ensure the desired loudness experience. Differences in scaling reveal individual loudness sensitivity and hyperacusis tendencies. Standardized scales (DIN 45631) ensure comparability between tests.

Speakers convert electrical audio signals into sound waves and are key components in free-field audiometry and sound reinforcement systems. Important parameters include frequency response, distortion factor, and directional characteristics. Calibrated studio monitors deliver precise levels for hearing tests, while consumer loudspeakers are optimized for sound aesthetics. Coaxial or dipole loudspeakers are often used in hearing studies to minimize reflections. Loudspeaker placement in a room influences reverberation and listening comfort and is planned acoustically.

Quality of life with hearing loss encompasses physical, psychological, and social dimensions, including communication skills, self-esteem, and social participation. Hearing loss increases the risk of isolation, depression, and cognitive impairment. Tools such as the HHIE (Hearing Handicap Inventory for the Elderly) quantify subjective stress. Interventions (hearing aids, rehabilitation, psychosocial support) aim to improve all areas of quality of life. Long-term studies show that early intervention significantly improves quality of life.

Line impedance is the complex resistance of an acoustic path, e.g., the middle ear or audio cable, to sound or signal transmission. It consists of resistive and reactive components and varies depending on frequency. In tympanometry, middle ear impedance is measured to assess vibration capacity and the ossicular chain. Deviations indicate stiffening (otosclerosis) or fluid accumulation. In hearing aid technology, impedance matching is used to ensure maximum performance and minimum reflections.

An auditory lexicon is the mental representation of sound patterns, words, and their meanings stored in the brain. It enables rapid word recognition and speech comprehension by comparing acoustic inputs with stored entries. Models of speech processing distinguish between phonological and semantic lexicons. Disorders such as aphasia or central auditory processing disorders impair access to the lexicon. In rehabilitation, lexicon access is trained through speech exercises and auditory training.

Lip reading is the technique of visually deciphering spoken sounds and words based on the movement of the lips, jaw, and facial muscles. It helps people with hearing impairments to improve their speech comprehension in quiet and noisy environments. Successful lip reading requires not only visual training but also knowledge of phonetics and speech rhythms. In practice, those affected combine lip reading with hearing aids or cochlear implants to achieve maximum communication ability. Speech therapists offer systematic exercises to synchronize visual and auditory impressions.

Lip synchronization refers to the adjustment of audio and video tracks so that lip movements and spoken sound are precisely synchronized. A lack of synchronization (lip synchronization errors) interferes with speech comprehension and can lead to cognitive overload. In subtitling and hearing aids with video streaming, precise lip synchronization is essential for correctly assigning speech sources. Technically, the delay is measured digitally and compensated for in milliseconds. Good synchronization improves the perceived naturalness and acceptance of audiovisual content.

The logarithmic scale represents values in exponential increments, allowing large data ranges to be displayed compactly. In audiology, sound pressure levels are measured logarithmically in decibels (dB) to represent linear hearing sensitivity. A doubling of loudness corresponds to approximately +10 dB, which is plausible and manageable on a logarithmic scale. Audiograms and frequency responses of hearing aids use this scaling to clearly visualize hearing thresholds and amplification profiles. Logarithmic representations facilitate the comparison of different levels and frequency ranges.

Speech therapy in auditory rehabilitation focuses on the linguistic and communicative abilities of people with hearing loss. Speech therapists train articulation, pronunciation, and sound comprehension using auditory-visual methods, including lip reading and sound therapy. They develop individual therapy plans to promote speech comprehension in everyday situations. In addition, they use auditory training and cognitive strategies to compensate for central processing disorders. Close collaboration with audiologists and psychologists ensures a holistic treatment approach.

Air conduction is the main hearing pathway, in which sound waves pass through the air into the ear canal, cause the eardrum to vibrate, and are transmitted to the inner ear via the ossicular chain. Tone and speech audiometry measure air conduction thresholds using headphones to determine the extent of hearing loss. Deviations between air and bone conduction indicate sound conduction problems or middle ear disorders. The air conduction curve in the audiogram forms the basis of every audiological diagnosis. Pathologies such as otoscopy findings are correlated with air conduction data.

An air conduction audiogram is a graphical representation of hearing thresholds across frequencies, measured by air conduction testing. It shows individual hearing curves and defines the degree of hearing loss, e.g., mild, moderate, or severe. The curve distinguishes between air conduction and bone conduction in order to differentiate between the causes of hearing loss. Standardized test frequencies range from 125 Hz to 8 kHz, and up to 16 kHz for high-frequency audiometry. Audiograms are essential for selecting and fitting hearing aids.

Airborne sound is sound that propagates through the air as a pressure wave and is heard via the outer ear. It differs from structure-borne sound in that the sound source consists of fluctuations in air molecule pressure. In room acoustics, airborne sound levels, reflection, and absorption are analyzed in order to optimize reverberation and echo. Hearing tests and noise measurements are based on airborne sound measurements using microphones. Hearing protection aims to reduce airborne sound levels below the limits that are safe for health.