The
work carried out at a truck sound lab is all about controlling
noise levels. A truck driver experiences a variety of different
sounds while working, some of which might be considered pleasant
but, for the most part, the work of the sound engineers focuses on
keeping unwelcome noise at a minimum. Volvo Trucks’ lets you have a
look behind the scene at their sophisticated sound lab.
Unlike many other areas relating to environment and safety,
research into noise is not necessarily driven by
legislation.
"The legal limit for noise in the work place in Sweden is 85 dB and
we are already down to 70 dB inside the cab", says Kaj Bodlund, a
senior technology specialist working with product development on
Volvo Trucks. "It's a question of comfort and, even more
importantly, safety."
"Low, monotonous sounds are known to reduce brain activity," adds
Christina Keulemans, Feature Leader, In-Cab noise at Volvo Trucks.
"The driver gets tired and, eventually, risks falling
asleep."
The noise made by on-board systems can also be disturbing for
drivers, especially when they are trying to sleep or rest.
Excessive noise from heaters, fans, air conditioning systems or
refrigerators could prevent the driver from sleeping soundly.
Drivers who are prevented from sleeping well are seldom the safest
or most efficient on the road.
At the sound lab at Volvo Trucks in Göteborg, Sweden, noise can be
tested in a variety of different ways. There are two sound chambers
for testing engine noise, one for engine and transmission noise, an
in-cab noise room, a reverberation chamber, as well as the vast
main testing lab, where the noise made by a complete truck can be
measured, using a simulated drive-by.
In the lab, tests are carried out using simulations, where a
computer registers and measures the decibel levels. In-cab noise is
measured using an artificial head with microphones in its ears. The
measurements are extremely accurate and very realistic. Real tests
are then performed on prototype trucks at Volvo Trucks' proving
ground outside Göteborg.
"We started using simulations and artificial heads in the 1990,"
Kaj Bodlund recalls. "Now we can carry out more tests in less time
and obtain more detailed data. In addition to decibels, we can also
measure frequencies and several other aspects of the
noise."
"In the lab we can separate different sounds. We can block
everything else and just measure and analyse the noise made
specifically by the engine, silencer or transmission system, for
example," comments Christina Keulemans.
Since Kaj Bodlund began his work on noise at Volvo Trucks almost 20
years ago, a great deal has happened. Back in the early 1990s,
in-cab noise levels of 74-75 dB were not uncommon. Today, they are
down to a far more tolerable 70 dB.
A major breakthrough in noise research was made in 1993 with the
introduction of the new FH range of Volvo trucks. The new, slim,
aerodynamic cab was not only better from the point of view of fuel
efficiency, it also considerably reduced wind noise. The air-tight
sealing of the cab also reduced noise from the engine and the
road.
"The new Globetrotter cab represented a considerable improvement on
the European market while, in the United States, it brought an even
more radical breakthrough in sound-proofing compared with their
existing products," recalls Kaj Bodlund.
The next significant development for in-cab noise came in 2002. The
Globetrotter cab was further improved by the addition of insulation
between the sheet metal and the trim panel. This reduced
condensation between the cab wall and the trim panels and improved
temperature control inside the cab, as well as making a
considerable difference to sound-proofing quality.
Over the years, the noise curve has progressed continuously
downwards. At some point, it will begin to even out.
"We realise that there will come a point at which we can't reduce
the general noise levels any more, but there is plenty more work to
do on more specific noise sources that may also impact the overall
driving experience. Squeaking, creaking or scratching sounds can be
equally unpleasant for the driver," explains Christina
Keulemans.
In 2006, a metal bolt was identified as the cause of a loud
vibration in the transmission, due to its unfavourable positioning.
The replacement of that single bolt enabled a considerable noise
reduction, amounting to five decibels.
"Our work is continuous and we still have a great deal left to do,"
Christina Keulemans emphasises. "Every time a design parameter is
altered or a new product is developed, we have to analyse the way
in which the change might affect the noise level."
The way in which the human brain registers sound is subjective.
Some sounds may be perceived as pleasant whereas others may be
disagreeable. Different individuals experience noises in a variety
of ways.
"In the future, we will not only develop ways of reducing noise,"
notes Christina Keulemans. "We will also have an opportunity to
create or emphasise sounds, depending on individual
preferences."
In surveys, most truck drivers want their truck to make as little
noise as possible, to enable them to use their communication
devices or listen to music without disturbance. However, some
drivers have said that they still like to hear that the truck is
powerful. Christina Keulemans envisages a future in which truck
drivers will be able to request a designed sound, based on their
individual preferences and their unique perception of what the
sound means.
"For instance, a subdued, quiet, solid sound would probably
represent luxury and quality, while a truck driver who appreciates
a powerful engine might actually want to hear what 700 hp sounds
like! It's all about dampening or highlighting different types of
sound for different purposes, she concludes."
Five factors that affect
noise levels
Mass:
A heavy component is less noisy (but of course heavy trucks consume
more fuel).
Insulation: The cab, the engine and many vibrating components can
be insulated with sound-proofing materials in order to keep noise
to a minimum.
Materials: Light metals such as aluminium may reinforce noise,
while heavy metals or rubber tend to dampen noise.
Damping materials: If parts and components made of sheet metal are
covered with damping materials, they generate less noise.
Aerodynamics: Wind noise is one of the worst noise offenders. An
aerodynamically optimised cab is both less noisy and more fuel
efficient.
Some common sounds with
an estimate of their decibel level
A whisper 15 dB
Normal Conversation 60 dB
Busy Street Traffic 70 dB
Vacuum Cleaner 80 dB
Large Orchestra 98 dB
Front Rows of Rock Concert 110 dB
Threshold of Pain 130 dB
Military Jet Takeoff 140 dB
Instant Perforation of Eardrum 160 dB