Acoustic shock (AS) is an involuntary trauma reaction, which can occur following exposure to a sudden unexpected loud sound, causing a specific and consistent pattern of neurophysiological and psychological symptoms.

What is AS?

With the rapid growth of call centres around the world, increasing numbers of call centre employees have been reporting an unusual cluster of symptoms following exposure to a sudden, unexpected, loud noise (acoustic incident) transmitted via the telephone line.

These neurophysiological and psychological symptoms are different to those occurring with a traditional noise injury, and have become known as acoustic shock (AS). AS becomes an Acoustic Shock Disorder (ASD) if symptoms persist.

Call centre staff using a telephone headset or handset are vulnerable to AS because of the increased likelihood of exposure, close to their ear(s), to an acoustic incident. More generally, AS can occur following exposure to any sound which gives a severe fright, is perceived as threatening or associated with a highly traumatic experience.

Westcott, M: Acoustic shock injury (ASI), Acta Oto-Laryngologica, 2006

Acoustic shock and TTTS Guide for Medical Professionals

Acoustic Shock Symptoms

Typical descriptions of an acoustic shock include "like being stabbed with an icepick in the ear", " like being electrocuted in the ear". For those using a headset, the immediate reaction is to pull it off.

The initial symptoms can include a severe startle reaction with a head and neck jerk, in extreme cases, falling to the floor; a stabbing pain in the ear; tinnitus; hyperacusis; sensations of burning, numbness, tingling and feeling of blockage in the ear; vertigo (dizziness, head spinning); nausea; a hearing loss or distorted hearing; and a shock response with shaking, crying, disorientation, headaches and fatigue.

Symptoms generally fade within a few hours or days. In some cases, some of the symptoms can persist for months or indefinitely. Persistent symptoms can include pain in and around the ear, pain in the neck/jaw/face, tinnitus, hyperacusis, balance problems or unsteadiness, headaches, facial numbness, a burning feeling in the ear or face, tingling, a feeling of pressure or fullness in the ear, an echo or hollow feeling in the ear, and a hearing loss.

AS symptoms are involuntary, so they cannot be readily controlled, and subjective, so they cannot be easily measured. The unusual symptoms may be misunderstood or not believed. As a result of an inadequate understanding of the symptoms, and if they persist or escalate, secondary and long term psychological symptoms can develop. These can include auditory hypervigilance, anxiety, depression, post traumatic stress reaction/disorder, fatigue, and anger.

Acoustic incidents

An acoustic incident is any sound which is perceived as threatening or highly traumatic. It is usually a sudden unexpected loud sound, usually heard near the ear. It may be a sound which becomes threatening because it persists and cannot be avoided. Acoustic incidents through a telephone line can originate as feedback oscillation, fax tones, signalling tones, or even malicious whistle blowing by dissatisfied customers. If the background noise level is high, call centre operators need to turn up the volume of their headset, increasing their risk of exposure.

A Proposed Mechanism of ASD - Tonic Tensor Tympani Syndrome

The primary cause of AS is considered to be excessive middle ear muscle contractions (stapedius and tensor tympani), in particular tensor tympani contractions, following exposure to a loud, unexpected sound. While the stapedial reflex is an acoustic reflex triggered by high volume levels, the tensor tympani reflex is a startle and protective reflex with a variable threshold to sound, which can be reprogrammed downwards.

Persistent ASD symptoms are consistent with a condition called tonic tensor tympani syndrome (TTTS). With TTTS, the tensor tympani muscle is spontaneously active, continually and rhythmically contracting and relaxing. This appears to initiate a cascade of physiological reactions in and around the ear without objectively measurable dysfunction or pathology. Symptoms consistent with TTTS can include: tinnitus; rhythmic sensations in the ears such as clicks and tympanic membrane (ear drum) flutter; alterations in ventilation of the middle ear cavity leading to symptoms in the ears of a sense of blockage or fullness, frequent "popping" sensations and mild vertigo; minor alterations in middle ear impedance (stiffness) leading to fluctuating symptoms of "muffled" or "distorted" hearing; irritation of the trigeminal nerve innervating the tensor tympani muscle, leading to pain, numbness and burning sensations in and around the ear, along the cheek, neck and temporomandibular joint (TMJ) area.

Our ASD program

Our Audiology practice provides unique expertise in the evaluation and management of ASD clients and in AS workplace consultancy. Ms Myriam Westcott is an audiologist with extensive experience in ASD and the rehabilitation of tinnitus and hyperacusis, dominant symptoms of ASD.

ASD evaluation and management

Our program involves:

  • A detailed medical history to provide a definitive diagnosis of ASD. Malingering or symptom exaggeration is generally rare in ASD clients, with many bewildered by their symptoms and desperate to recover. However, as the symptoms are involuntary and subjective, and generally a third party will be funding the evaluation and treatment of the injury, a careful and considered diagnosis needs to be made.
  • A hearing assessment needs to be carried out with care. For clients with severe ASD many sounds are painful, potentially leading to a temporary exacerbation of their TTTS symptoms. Additionally, clients with severe ASD are unable to tolerate anything placed in or over their ears without temporary exacerbation of their symptoms. As a result, an audiological assessment, requiring the client to listen to sounds via headphones/earphones, is threatening and can lead to a significant temporary increase in symptoms. Suprathreshold audiological testing, including loudness discomfort testing, and in particular acoustic reflex testing due to the high volume levels required, should not be carried out with ASD clients.
  • An evaluation of the emotional impact of ASD is carried out, which screens for clinically significant levels of depression, anxiety and post traumatic stress disorder or trauma reaction.
  • To provide understanding and reassurance, we give a detailed explanation of ASD to our clients. This includes a personalised explanation of the peripheral and central auditory system, including TTTS; hearing test results; the neurophysiological basis of hyperacusis, tinnitus-related distress, and auditory hypervigilance.
  • A detailed report is provided to evaluate ASD, including fitness for work place duties, recommendations for a personalised rehabilitation program and onward referral for further evaluation and management of medical and psychological symptoms as required.

ASD Rehabilitation

Symptoms are individually managed as follows:

  • We provide therapy for the dominant symptoms of tinnitus and hyperacusis
  • We provide audiological management of hearing loss, including hearing aid fitting if required
  • We recommend medical management of symptoms such as pain and vertigo
  • We provide management of psychological symptoms. These can include stress and sleep management strategies; and the personalised development of cognitive behavioural strategies to manage auditory hypervigilance. For severe ASD, psychological/psychiatric evaluation and treatment for anxiety, depression and post traumatic stress disorder may be required and referral will then be recommended.

AS Workplace consultancy

The potential severity and persistence of ASD symptoms has significant clinical and medico-legal implications. Call centres in Australia are starting to become aware of the risk of AS and the need for AS workplace management. To provide effective AS protection in the workplace, the following factors should be considered:

1. We provide an AS Audiological Workplace Program, which includes:

  • A workplace AS risk assessment.
  • A hearing assessment for employees and supervisors.
  • An AS education program for employees and supervisors.
  • An AS protocol to be followed if an employee develops symptoms consistent with AS, which includes an AS assessment and rehabilitation for the employee. Rapid referral of affected staff can help to control persistence or escalation of symptoms.
  • An AS reporting protocol to ensure that the employer can manage risk consistently and meet insurers' needs should a WorkCover claim arise.
  • The protocol to be followed should an employee be considered potentially unfit to perform their usual workplace duties.

2. Workplace environment: Ambient noise management. The higher the levels of ambient noise, the higher the required volume level of the telephone headset amplifier for the caller's voice to be clearly audible, increasing the risk of AS. An acoustician will be able to measure ambient noise levels and teach effective communication strategies to minimise ambient noise levels. We do not provide this service, but can recommend companies who do.

3. Telephone headset protection to acoustic incidents. A number of output limiting devices have been developed to restrict maximum volume levels transmitted down a telephone line, and are of benefit to help reduce the probability of acoustic incident exposure. Technicians are available to evaluate and recommend appropriate devices. We do not provide this service, but can recommend companies who do.


The dominant factors leading to AS appear related to the sudden onset, unexpectedness, impact quality and threat response to loudish sounds outside the person's control, rather than to high volume levels alone, so output limiting devices are not able to provide total protection against acoustic incidents. Employees with persistent ASD symptoms remain vulnerable to an escalation of their symptoms following further acoustic incident exposure and for this reason should not return to headset use even with output limiting devices in place.

What is AS?

Our ASD program

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