Noise Audiometry: Treatment, Effect & Risks

In Langenbeck’s noise audiometry, the hearing threshold is determined for different pitches with simultaneous superimposition of the pure tone with a background noise. The audiometric test allows conclusions to be drawn about whether sensorineural damage is present, that is, damage in the sensory system (sensors in the cochlea) and/or in the downstream neural area. The method was developed and presented by Bernhard Langenbeck as early as 1949 and 1950.

What is noise audiometry?

The audiometric test allows conclusions to be drawn about whether sensorineural damage is present, i.e., damage in the sensory system and/or in the downstream neuronal area. Noise audiometry according to Langenbeck differs from “normal” tone audiometry in that, in addition to determining the hearing threshold for frequency-dependent tones in the form of absolute or relative sound pressure levels, the individual tones are underlaid with a noise of constant intensity. The sound pressure level of the noise is selected in such a way that it covers the individual resting hearing threshold in the middle frequency range, but is below the hearing threshold for pure tones for high and low tones. The procedure primarily allows conclusions to be drawn as to whether, in the case of reduced hearing, the cause is damage to the sensory cells in the cochlea or damage to the downstream transmission pathway (auditory nerve) or the neural processing centers. In the case of an impaired function of the receptors in the cochlea, the subjects experience a less pronounced masking of the pure tones to be heard than in the case of a downstream nerve-induced hearing loss. Clarification about a possible conductive or sensorineural hearing loss can be made in advance by comparing the hearing thresholds between structure-borne sound and air-borne sound.

Function, effect and goals

If a hearing loss is suspected, it is first of interest to confirm or eliminate the suspicion by means of subjective and objective tests. If a hearing loss is confirmed, it is necessary to find out what the causes of the impaired hearing are in the interest of successful therapy. In principle, mechanical-physical impairments may be present, such as an external auditory canal clogged with earwax, or the eardrum may be damaged and its function temporarily or permanently impaired. In some cases, the ossicles that mechanically transmit sound are also diseased or calcified (otosclerosis), leading to problems in sound conduction. Other causes may be a functional impairment of the sensory cilia in the cochlea, which convert the “heard” sounds into electrical impulses, or there may be problems in the downstream neural processing of the auditory signals. If a sound conduction disorder can be excluded, so that a sound perception disorder can be assumed to be the cause of a diagnosed hearing loss, sound audiometry according to Langenbeck represents an extended diagnostic procedure. Similar to a “normal” audiogram, pure tones of different pitch are played into the left or right ear of the test person or patient via headphones and simultaneously superimposed with a permanent noise. This is so-called “white noise”, which has a constant power density in a limited frequency spectrum. The sound pressure of the noise is chosen to be above the perception threshold for medium frequency sounds (1 to 4 kHz), but below the perception threshold for low and high tones. In contrast to audiograms without background noise, for which individual hearing thresholds are usually entered as deviations relative to normal values, it is common practice in noise audiometry to enter hearing thresholds as absolute sound pressure levels on an appropriate form. This makes the influence of the background noise on the hearing threshold of the pure tones clearly visible. The results of the test procedure according to Langenbeck indicate whether a neural or a sensory problem is present. In the case of sensory (cochlear) hearing loss, pure tones are less masked by background noise than in the case of neuronal hearing loss.In the case of cochlear-related hearing loss, the pure-tone points – similar to those of persons without hearing problems – lie at the level of the noise and, in the case of the low and high tones, merge into the resting hearing thresholds not backed by noise. In the case of a neuronal hearing loss, the pure tones are perceived by the patients only at a higher sound pressure than the noise. In the recording diagram, the hearing thresholds of the pure tones are therefore always below the “noise level”. They are, so to speak, evading the unobscured quiet hearing threshold. The recorded hearing threshold points in the diagram for noise audiometry according to Langenbeck already give a clear visual indication of whether there is a cochlear or a retro-cochlear, i.e., a downstream neuronal, problem.

Risks, side effects, and hazards

Audiograms are not only used to detect and localize conductive or sensorineural hearing loss, but can also be used to demonstrate that the subject’s hearing is within a predetermined range of normal hearing. For example, this is a common practice for determining fitness to fly for commercial and airline pilots. In cases where one of the two ears has significantly poorer hearing, the problem of “overhearing” arises. The ear with the better hearing is more likely to perceive the sound played through headphones than the “worse” ear, which can falsify the results of the audiogram because the patient does not realize that he is perceiving the sound to be detected with the “wrong” ear. Overhearing usually happens when the hearing threshold of the worse ear is more than 40 dB higher than that of the better hearing ear. In order to still obtain an unbiased result, the better ear is “deafened”. A loud noise is applied to it in order to temporarily desensitize it to the test sound. When setting the sound pressure level for the numbing noise, attention must be paid to the discomfort threshold above which the noise is perceived as uncomfortable or even painful. No other hazards or side effects of a Langenbeck noise audiogram are known.