Appendix
72
Functional Description of the Hearing Protection
1. Basic Principles of Hearing Protection
Background
The human hearing is one of the most important and sensitive sense organs. Therefore, hearing protection is essential for people who are
exposed to high sound pressure levels for a longer period of time. It is even of existential importance for people who need a good hearing
for their profession such as musicians, sound engineers, interpreters or radio moderators.
Problem
Like a sunburn which is noticed when the skin has become red already, it is found out that the noise level was too high when the ears are
already “ringing”. In both cases it is too late to think about protective measures.
State of the Art
The current offer of electronic hearing protection includes more or less the use of audio limiters only. For an extensive hearing protection
the limiting of the electric output signal with a limiter is not sufficient. Instead of this the actual sound pressure the user is exposed to has
to be registered, evaluated and regulated during the whole time of listening. The target is that the listener cannot reach a critical noise dose
over a long period of time of listening.
2. Function of EarPatron
The EarPatron technology implemented in the SIS interpretation system contains the following functions:
“Headphone-Adapt” Technology
Depending on the technical specifications, each headphone produces a different sound pressure with the same output level of the
headphone amplifier. For this reason the “Headphone Adapt” technology has been developed. The measured electrical values are put into
relation to the used headphone. After entering the technical specifications of the headphone, EarPatron is able to use the actual sound
pressures as basis of all calculations, because electrical values are in direct relation to the acoustical impact. In conjunction with the SIS
interpretation system the adjustable headphone level is limited to a maximum of 105 dB(A) with full modulation of the data bus and right
stop of the volume control.
“Noise Fuel Gauge”
As the “Headphone Adapt” algorithm is used to find out the actual sound pressure at any time, EarPatron is able to sum up the level of
noise already arisen over an arbitrary period of time. This is converted into a percentage value of the rating sound level (maximum noise
level) of 85 dB(A) for 8 hours. A rise of the noise level by 3 dB results in a splitting of the permitted time (e.g. 88 dB(A) for 4 hours,
91 dB(A) for 2 hours etc.). This rating sound level must not be mixed up with the maximum sound pressure level that can be achieved (here
105 dB(A) at 1 kHz), as the effective sound pressure is regarded in proportion to the working time. A sound pressure of e.g. 119 dB(A) for
10 seconds results in the same noise level as an 8-hour sound pressure of 85 dB(A).
The interpreter station displays how much percentage of this value has been achieved already. 10% means: „A lot of noise still may be
given“, 100%, however, means: “You have already received the whole daily ration of noise”.
The “noise fuel gauge” is always displayed, no matter if EarPatron is switched on or off. Therefore, even a user, who does not want an
automatic control of the hearing volume (EarPatron switched off), can check if his listening habits are “healthy”. A displayed value of more
than 100% means: “The hearing volume has been too high for the duration of the work”. Furthermore, it is helpful to develop a feeling
for the consequences of high listening levels, because an increase of the volume automatically increases the display of the “noise fuel
gauge”.
Intelligent EarPatron Control
EarPatron can control if the noise level for the user is still in a safe area or if it makes sense to reduce the hearing volume. This happens so
that the intervention is performed smoothly and unnoticed. With a progressive hearing duration, the hearing level is reduced continuously
so that the maximum noise level (100%) is usually never reached. Should the maximum noise level, however, be reached due to unhealthy
listening habits (or EarPatron was activated when the noise level had exceeded 100%
already), the algorithm will reduce the volume level so that no serious volume (> 85 dB (A)) can be achieved anymore. This allows continuous
work at relatively safe audio levels without fearing additional stress of the hearing.
The EarPatron algorithm works without automatic reset. This means that breaks of the user, when the hearing volume is set to “0”, are not
evaluated as recreation phases for the hearing. EarPatron can be reset with “Reset” only. The reason why is that the noise level the user is
exposed to during a break is unknown. It is unknown, if the hearing of the user really could recover or if it was exposed to a higher noise.
This means the “noise fuel gauge” will not reduce, even when the hearing volume has been “0” for a longer period of time. EarPatron
cannot take into account the whole daily routine of the user, but with EarPatron and the SIS interpretation system the stress of the hearing
can be kept harmless.
