The work at DHZ

Get your hearing back at last!

Hearing problems are all too common in our society – in Germany, around 15 million people are affected. The good news: All the different kinds of hearing issues can now be diagnosed and treated. Whether it’s an operation, a hearing aid or an implant – there are lots of options for restoring your hearing. And who does this? The German Hearing Centre (Deutsches HörZentrum or DHZ) in Hanover works with a team of experts, using the best possible forms of therapy for patients. Find out more here about what makes DHZ special, what future hearing solutions they’re working on – and listen for yourself to find out what a hearing issue sounds like.

15 million people …

in Germany suffer from hearing disorders, ranging from hearing impairments through to complete deafness. Hearing loss is one of the most common health conditions in Germany.

2003 …

the German Hearing Center Hanover (DHZ) was founded. It is part of the ENT clinic run by the Hanover Medical School (Medizinische Hochschule Hanover – MHH) which only uses state-of-the-art technology when conducting diagnostic methods and surgical treatments.

An all-inclusive …

service is offered by the DHZ. The Centre uses sophisticated methods to diagnose hearing impairments, provides advice on the use of hearing aids, performs surgery and provides medical, technical and educational support to patients over the course of their lives.

A centre of excellence …

the DHZ is part of the”Hearing4All” centre of excellence. Together with our partners from the fields of science, research and medicine, the DHZ is helping to shape the future of hearing in a dramatic way.

Teamwork …

is our watchword here at the DHZ. ENT specialists, medical engineers, educators, speech therapists, hearing care professionals, manufacturers of hearing devices, scientists and developers of medical products work alongside Professor Thomas Lenarz and engage directly with patients.

All the latest hearing system models …

are available at the DHZ, including conventional hearing aids, middle ear implants, cochlea implants and tinnitus maskers. Our experts also use brainstem implants and middle ear implants – the MHH’s ENT clinic was actually the first clinic in the world to implant middle ear implants.

Cochlea implants …

are a speciality at the DHZ. Our ENT clinic is known around the world for having the world’s most extensive cochlea implant programme. So far, around 10,000 adults and children have received implants here (as at 3/2019). Approximately 600 new patients a year receive a new cochlea implant.

Time to listen:

How our hearing works

The ear is the first organ to start working when we develop. We can hear when we are only 21 millimetres in size as an eight-week old embryo inside the womb. Our ability to hear has fully formed by the time we are 18 weeks old. Expectant mothers observe this when their unborn children clearly respond to sounds, especially music or the sound of their parents’ voices.

Two factors play a key role in this process: Frequency (or pitch) and volume, which is also known as sound pressure or sound level. The frequency is the number of vibrations per second which is measured in hertz (Hz). The sound level is measured in decibels (dB).

Because the sound level is relayed from the ear canal to the ossicles in varying degrees of intensity, the way we perceive volume also depends on the frequency of the sound. The sound spectrum perceivable by humans ranges from approximately 16 hertz to a maximum of 20,000 hertz, however, the ability to perceive high frequencies diminishes as we get older.

Lower frequencies exist outside our range and are called infrasound. Elephants can hear the lower frequencies, and dogs, dolphins and bats can hear the higher frequencies which are called ultrasound.

What do we mean by loud?

How sounds influence us

You will recognise this phenomenon if you have ever spent an evening burning up the dance floor. When you leave the nightclub, voices and noises sound muffled. The music was so loud that your hearing has been deadened for a while. This is no surprise because the music in the club is over 100 decibels, which is as loud as a sawmill! Read hear to find out what our ears have to withstand during everyday life. Did you know that a rock concert is as loud as a jet engine?

Hearing impairment

What does this sound like?

People with normal hearing find it hard to imagine what it is like for people who are hard of hearing. It’s time to find out! The following examples demonstrate in a striking way how differences in the degree of hearing loss can influence the way sounds are perceived. This gives us an insight into how much quality of life must be impaired for those affected by hearing loss, especially when we live in a world dominated by communication, making it very difficult to take an active part in everyday life.

Normal volume

Decrease of 30 decibel

High frequency attenuation 4000 hertz

High frequency attenuation 2000 hertz

High frequency attenuation 1000 hertz

High frequency attenuation 5000 hertz


The hearing loss spectrum

A few things can happen between the outer ear and the brain that cause permanent damage to hearing. A genetic predisposition can be responsible in some cases, whilst stress, accidents and medications can be other contributing factors. The hearing loss spectrum is wide and ranges from slight hearing problems to complete deafness. 20 per cent of the population in Germany suffer from some degree of hearing impairment which equates to around 15 million people. Even though the individual causes of hearing loss may be varied, the consequences are the same for all those who are affected. They have reduced education and career opportunities and there is an increased risk of social isolation. Let’s take a look at the hearing impairment spectrum.

Middle Ear Deafness

Hearing impairment in the middle ear, otherwise known as conductive hearing loss, can generally be treated with surgery. The most simple form, such as a middle ear effusion, can be treated with paracentesis. A middle ear operation can help to resolve chronic inflammation or damage to the middle ear that occur due to accidents or illnesses. The ossicles are reconstructed during this procedure. Passive ossicular replacement prostheses, or ossicle implants, are able to perform the role of the natural ossicles.

Inner Ear Deafness

Hearing impairments in the inner ear can only be treated with medication if the condition advances quickly. Hearing aids are usually used if the patient slowly develops sensorineural hearing loss over a longer period. Over recent years, huge advances have been made in terms of the shape and the technology used in conventional hearing aids. Alternatively, it is possible to opt for a partial or complete middle ear implant which can especially make it easier to distinguish speech from background noise. Electrical hearing aids known as cochlea implants (CI) are suitable for profound sensorineural hearing loss. Please read this article to find out more about CI.

Mixed Hearing Loss

In the case of mixed hearing loss, conductive hearing loss in the middle ear occurs at the same time as sensorineural hearing loss in the inner ear. It is very important that there is sufficient ventilation in the middle ear. If this is the case, the hearing aid does not need to be amplified too much. It has recently been possible to combine both passive and active middle ear implants.


A cochlea implant can be used in a deaf patient if the auditory nerve is still intact. If the auditory nerve is damaged, a brainstem implant or an auditory midbrain implant may be considered.

Tinnitus (Ringing in the Ears)

Each tinnitus patient perceives sounds in a different way, ranging from a continuous buzzing sound, ringing or whistling in the ears (subjective tinnitus). It is very rare for the ringing sounds to be heard by the doctor (objective tinnitus). It is usually not possible to find one single cause or one single therapy that is immediately effective for most cases of long standing tinnitus. Tailored therapies help to greatly reduce – or completely mask – the ringing sounds and the patients’ sensitivity to noise.

Tinnitus help

⇒ Better to intensify or to mask?
The device known as a “masker” looks like a small hearing aid and masks the sound of the tinnitus by creating a noise itself. The affected ear perceives the tinnitus and the masker at the same time which makes it feel as if the actual tinnitus is pushed into the background. Alternatively, it is possible to combine the masker with a hearing aid so that a defined noise is emitted in the inner ear which masks the tinnitus.

⇒ A Trailblazer for the Auditory Nerve:
The Tinnelec Implant restores the normal electrical discharge patterns in the auditory nerve using electrical stimulation. It is composed of an outer part, which is attached behind the ear, and an inner part with electrodes, which is placed externally on the cochlea. The Hanover Medical School is currently using Tinnelec in a clinical study.

Cochlea implant

The cochlea implant or how a dream came true in hearing research

What can a cochlea implant do?

The most common causes of profound hearing loss and deafness are defective hair cells in the cochlea. As these sensitive sensory cells are unable to repair themselves or regrow, deafness is initially incurable. But the good news is that this can be overcome using a technical solution: cochlea implants (CI). The system takes over the job of the defective auditory sensory cells and converts sounds into electrical signals which the auditory nerve then relays to the brain where they are decoded and interpreted. This enables the hearing impaired person to recognise sounds, music, and, most importantly, speech.

How is the implant used?

The CI is composed of two parts: an electrode in the cochlea and a speech processor behind the ear which transfers the information to the implant via a coil. This is attached to the head by means of a magnet. Specialists from the German Hearing Center insert the electrodes into the cochlea during an operation which takes around two to three hours. During the operation, they check the functioning and position of the electrodes in the cochlea. Despite its infinite complexity, this has now become a standard procedure at the MHH. The structures in the cochlea are protected by this process which ensures that any residual hearing remains intact.

What is so special about the implant?

CI has turned the dream of replacing a human sensory organ into reality for the first time and it now plays an important role in the clinic’s routines. The ENT clinic at the MHH is the world’s largest referral centre for cochlea implants and cares for round about 600 new patients every year. Since 1984, experts at the MHH have helped well round about 10,000 people to hear again.

How does the world sound with a cochlea implant?

In a healthy ear thousands of hair cells transfer auditory information to the brain; 12 to 22 electrode contacts take on this role in a CI. This large amount of compression can be felt on a sonic level, but the brain can piece together a good sound pattern from this simulated, electronic information and ultimately even recognise speech via a telephone.

Hearing Aids of the Future

How hair cells regenerate

The varied types of cells in the inner ear means it can be very challenging to administer effective treatments. Regenerated hair cells in the inner ear can only function if they are located in the correct position. The ENT clinic at the MHH is aiming to use a special positioning system which will make it possible to carry out a targeted stem cell transplantation procedure to replace damaged hair cells in the inner ear.