Bowman Team Partners With Racal Acoustics To Deliver Improved
“A massive improvement” was the verdict of the trials team leader from
the 3rd Yorkshire Battalion tasked with putting Racal Acoustics’ iCombat Active
Noise Reduction (ANR) communications headset through its final paces on Warrior
earlier this year. Initial prototypes were demonstrated on CVRT Scimitar at the
Armoured Trials & Development Unit, Bovington, Dorset in July last year and
production units were trialled in January 2007. The headset has entered
operational service in April 2007.
The RA195 Combat headset is a high performance headset designed specifically to overcome the noise
and operational environment of tracked vehicles. It incorporates both ANR and
Talk-Through technology that provides 360 degree situational awareness. The
iCombat headset is an improved version of the successful Combat headset.
Colonel Hudson, Bowman
Delivery Manager, was “very pleased” with the outcome and keen to stress that
“delivering these product enhancements, on-time, confirmed Racal Acoustics’
industry leading position”. Racal Acoustics is committed to continuous product
improvement and have a number of technology insertions planned. They look
forward to working closely with the MoD to deliver more capability and reduced
whole life costs across their range of headsets, handsets, telephones &
systems and avionics products."
TECHNICAL EXPLANATIONS OF THE SPECIAL TECHNOLOGY
USED IN THESE HEADSETS FOLLOWS;
Localized situational awareness is the ability of the user to be able to
sense their immediate surroundings while wearing a communications headset.
Headsets that occlude (cover or block) the user's ears can impair their
natural situational awareness. Racal Acoustics' Talk-Through functionality
gives users 'their ears back' and restores natural situational awareness. The
added benefit of Talk-Through is that the user’s hearing is protected from
impulse noises, such as weapons discharge and explosive blasts.
Through independent laboratory-based verification and in-field
evaluations. Racal Acoustics' Talk-Through functionality has been determined to
provide better sound localization than any other communications headset.
While it is vital that headset users are able to hear what is happening
in their immediate surroundings (to provide situational awareness), protection
is required to ensure temporary or permanent noise-induced hearing loss does
not occur due to events such as small arms fire or explosive blasts.
Talk-Through allows users of communication headsets to hear sounds
external to the headset, without having to remove the apparatus and thereby
maintaining platform intercom or radio communications integrity.
The electronic reproduction of the external sounds ensures that near
natural hearing is accomplished while the Talk-Through feature is activated. Talk-Through
is enabled and disabled through a control button located either on the control
box (switchbox) or on the headset, depending on the exact model.
Small microphones, mounted externally on the either side of the headset,
pick up the external sounds.
These sounds are processed electronically and mixed (combined) with the
platform intercom or communications signals into each earshell.
The stereo Talk-Through signal is a faithful reproduction of the
external environment; localisation is the ability to detect sound direction
through superior electro-acoustics design of both the headset (earshell) and
the Talk-Through circuit.
Talk-Through has in-built protection which ensures the sound level
reaching the user’s ears (presented by the Talk-Through system) does not
exceeds 85 dB(A).
This protection is especially important when personnel are dismounted
and operating in an environment with a high probability of weapons discharge or
explosive blasts. The onset and recovery time of the Talk-Through circuit are
rapid, allowing normal communications and Talk-Through almost immediately
following the impulse noise.
This protection is achieved by the Talk-Through circuit actually
'compressing' the peak sound pressure, as opposed to merely 'clipping' the
sound. This has the advantage that the radio or platform communications can
still be understood during this noise exposure.
There are compelling reasons for achieving noise reduction in military
environments because of the high sound levels that frequently prevail.
Noise can severely impair communication; at best it is fatiguing and can cause
short term hearing impairment, at worst, it can lead to permanent hearing
damage. Health & safety, soldier effectiveness and mission success can all
be compromised by noise.
Levels can range anywhere from the medium noise found in tactical
wheeled vehicles, typically mid-90 dB(A), to high levels over 110 dB(A) in
tracked vehicles, to extreme levels approaching 150 dB(A) experienced by ground
crews working around fast jets. As a ‘medium level’ of 95 dB(A) is
actually high in civilian workplace terms, it is understandable why clear
communication at higher military noise levels is so crucial.
Noise reduction is the attenuation of sound energy reaching the ear,
achieved through either the creation of a physical barrier that stops the
energy, known as Passive Noise Reduction (PNR), or by so-called anti-noise
techniques called Active Noise Reduction (ANR) or even a combination of the
In the case of a communication headset, noise reduction, in its simplest
form, is typically achieved by blocking the noise path using earcups sealed to
the head by means of a soft earcushion.
What is Passive Noise Reduction
PNR is the attenuation of acoustic noise by the creation of a physical
barrier between the sound source and the ear. This is achieved by the specific
design of the barrier, in the case of a typical military communications
headset, the earshell. The construction of the earshell, material mass, volume
and stiffness, coupled with the compliance of the seal between the earcushion
and the head, provides the mechanism to achieve passive attenuation. Such
passive techniques are most effective at higher frequencies.
The integrity of the seal has a significant impact on the attenuation of
the headset and is normally aided by a spring that exerts force on the earcups
and ear cushions. The spring mechanism can be over the head (headband) or
behind the head (neck/nape band). Force can also be applied without a spring by
means of strap arrangement, as is the case with some Combat Vehicle Crew ( CVC
The neckband is the established means for mechanized infantry, enabling
operatives to ‘don & doff’ headsets without having to remove ballistic
helmets. Headsets are worn both mounted and dismounted, and helmet design is
changing to better accept the headband, for example with the US and Australian
advanced/enhanced combat helmet ( ACH / ECH ).
However, as with many engineering solutions there are sometimes
compromises to be made. Too much spring pressure results in wearer discomfort,
too little means the headset is not secure. Similarly, if the earcushion is too
soft it becomes ineffective, too hard and it becomes uncomfortable. There is
also a limit on the physical size of the earshell, which needs to be compatible
with ballistic protective equipment, such as helmets. Human factors have
generally become much more relevant in recent years and it is no longer just a
question of technical performance. Nevertheless, PNR is most effective at
higher frequencies with any ‘shortfall’ in attenuation at low frequencies being
complemented by ANR .
What is Active Noise Reduction?
ANR is an electronic means of attenuating lower frequency noise
(applicable where passive techniques alone are inadequate) using the principle
of anti-noise. Due to ‘the physics’, ANR is most effective below a frequency of
1kHz. It works best in confined acoustic environments and thus ideally suited
for use in a headset earshell. ANR is based on closed loop feedback, whereby a
small sense microphone, located in the earshell, detects noise appearing at the
ear. The signal is filtered and amplified before being fed back to the earphone
to generate an identical acoustic signal that is in anti-phase. This has the
effect of cancelling the noise, thereby improving the audio signal. The circuit
incorporates a pre-amplifier, feedback filter and drive amplifier. A stability
control mechanism is essential for the correct operation of the ANR system in a
dynamic environment, for example, soldiers in vehicles moving quickly over
There are two basic implementations:
baffle across the earshell that creates a front and a back cavity.
self-contained ANR Module approach.
The module approach benefits by preserving a greater amount of the
volume within the earshell, which, in turn, enables a higher level of passive
noise reduction to be achieved. Additionally, a module is easier to retrofit to
passive earshells on an upgrade or OEM basis.
The electronic ANR Module uses a closed loop feedback circuit. A
small 'sense' microphone is positioned in the earshell cavity to detect the
noise appearing at the ear. The signal is filtered and amplified and is then
used to drive the earphone, also inside the earshell, to generate an identical
acoustic signal which is in anti-phase (180 degrees phase shifted to the
The introduction of the real time anti-phase signal within the earshell
results in a high level of cancellation, which can reduce the low frequency
energy by up to 97%. This, when combined with the passive attenuation of the
headset, provides a broadband noise reduction performance of 30 dB(A).
The heart of the module is a Racal designed electronic circuit, which
incorporates the speech pre-amplifier, feedback filter and drive amplifier, and
additionally provides the overall system stability control essential for
correct operation in a dynamic environment. The circuit is mounted on a small
Surface Mount Technology PCB, which also accommodates the passive components
needed to optimize and interface the ANR system for specific applications.
By using this approach, the overall size and weight of the ANR system is
minimised, allowing its incorporation in the earshell of the headset without
the typical degradation of passive attenuation associated with other methods of
The electronic PCB is mounted on a small plastic moulding, which also
houses the earphone transducers and sense microphone. The board is sealed to
the moulding to maintain the integrity of the acoustic transfer function and
the component side of the board is internal to the module to provide a higher
level of handling and environmental protection.
In addition to the ANR earphone, a second conventional service type
earphone is provided for communication such that, should the ANR circuit or ANR
earphone fail, communications will still be received. This reversionary mode enables
the headset to be used as a conventional headset when required. If required, a
switch can be provided on the headset to disable the ANR circuit when used in
the reversionary mode.
Effects of Noise on Hearing
Good communication is essential in military activities. Apart from a
reduction in effectiveness, miscommunication can have a major impact on
personal safety and ultimately compromise the success of a mission. Exposure to
noise, even for short periods of time, can lead to hearing impairment, known as
temporary threshold shift (TTS).
The amount of TTS is a function of noise exposure time and the sound
level of the noise source. Fortunately, hearing will recover if further
exposure is prevented. The period of recovery is dependant upon the amount of
TTS, ranging from just a few minutes through, in extreme cases, to a recovery
time of many hours.
Induced Hearing Loss
For personnel exposed to a high level noise with a high TTS or where the
TTS has not completely recovered before further exposure to noise, a permanent
threshold shift (PTS ) can occur. This is a result of the hearing organ
beginning to degenerate and this damage is irreversible and can eventually
result in a loss of hearing.
Institute on Deafness and other Communication Disorders - http://www.nidcd.nih.gov/health/hearing/noise.asp
Safety Executive - http://www.hse.gov.uk/noise/keyfacts.htm
American Academy of Family Physicians -http://www.aafp.org/afp/20000501/2749.html
The effects of work-related noise on hearing have been known about since
the Industrial Revolution. Evidence of the effects of noise on hearing has been
well documented in the U.K.’s shipbuilding industry, where it was known as
‘boilermaker’s ear’. However, it was not until studies were carried out in the
1950s that the relationship between high noise levels, length of exposure time
and the increased risk of noise induced hearing loss (NIHL) was quantified.
NIHL is insidious since it happens over time and often goes unnoticed.
Although workplace legislation in the U.K. and U.S. dates back to the
1970s, for many years ‘the military’ were exempt from such legislation and
immune from prosecution. However, this position changed in the 1980s.
The exact detail of the legislation differs from country to country but
fundamentally it places maximum limits on exposure levels and the time
operatives may be exposed. This combination of level and time forms the concept
of noise dose and it is the accumulation of noise dose over time that increases
the risk of NIHL.
For example, the same daily noise dose can be achieved by 90 dB(A) for 4
hours or 93 dB (A) for 2 hours or 87 dB(A) for 8 hours.
There is also a separate limit on the peak noise caused by impulsive
sources, such as weapon discharge or explosives. Not only does repeated
impulsive noise quickly lead to a high noise dose, temporary shift and the risk
of permanent NIHL, it can also cause instantaneous damage to the ‘mechanical’
parts of the ear, as with a burst eardrum.
Agents Noise Directive
Most recently, the Physical Agents (Noise) Directive has been imposed
Europe-wide and has been implemented in the U.K. as the Control of Noise at Work Act (2005),
replacing the earlier Noise at Work
The 2005 Regulations requires employers to take action to protect
workers at levels of noise 5 dB(A) lower than in the 1989 Regulations and now
require health surveillance (hearing checks) for those regularly exposed noise
above 85 dB(A).
For more detail it is advisable to refer to the agency tasked with
enforcing the legislation, which in the U.K. is the HSE, who have an
informative website www.hse.gov.uk/noise.
Understanding Decibels (dBs)
When considering noise measurement, the range of levels of interest is
in the ratio of about 1,000,000,000,000,000,000 to 1. With numbers of this
range and magnitude it is much more convenient to use a logarithmic scale to
provide numbers which are far easier to comprehend and use.
The decibel scale is thus a logarithmic ratio between any two sound
levels. For example, the ratio given above may be written as 180dB. The
addition or subtraction of decibels is different to normal linear calculations.
Adding 3dB to an existing noise level doubles it. So 93dB of noise is twice
90dB of noise. Adding two noise levels of 80dB does not give a noise level of
160dB, but gives a level of 83dB; i.e. twice the 80dB noise level.
The decibel measure is also applied to hearing protected headsets to
describe their 'average attenuation' or 'insertion loss' (noise reducing
effect). For example, if an individual is working in a noise level of 105dB at
a frequency of 1kHz then wearing a protective headset with an average
attenuation of 30dB at 1kHz reduces the effective noise level to 75dB at that
Wikipedia Link http://en.wikipedia.org/wiki/Decibel
Salford University http://www.acoustics.salford.ac.uk/acoustics_info/decibels/