Sound Quality Design - Rieter

Sound Quality Design
Trends in Vehicle Acoustics
he cars on European roads are 10
T times quieter than they were 20
years ago and standards have been set by
the European Union requiring a further
significant drop in traffic noise by 2010.
From the consumer side, expectations of
vehicle comfort are also increasing, which
has compelled the highly competitive car
industry to offer ever-quieter new models.
In light of these strict regulations and market
forces, the importance of acoustics or NVH
(Noise Vibration Harshness) in the design of
road vehicles immediately becomes clear –
so much so that a great deal of the design of
an acoustic package is done in the very early
stages of this process, on virtual models.
These models allow for simulation and
measurement of the single components of a
vehicle, including the acoustics. Performance
can be predicted and refined well before the
car, van, or truck takes to the road.
The Power of Simulation
Many challenges are on the table here - noise
is present both inside and outside a vehicle.
Exterior noise is typically the engine, the
exhaust, and tyre noise on the road; this white
sound combines to generate noise within the
passenger compartment. Noise can be either
airborne or structure borne and belongs to
three frequency fields: low (equivalent to the
sound of a powerful exhaust), mid (like the
sound of a jet plane) and high (comparable
to a whistling sound). Ways must be found
to deal with these types of noise sources at
any frequency – the mid and high frequencies
particularly create the most difficulties.
Complex software and computing power is
needed so that the simulations and predictions
can serve in the design of vehicles before
the first run on the test track, when it is far
too late to make modifications. Furthermore,
prototypes are a costly item, so the more
testing and validation that can be done well
beforehand the better.
NVH experts are continually developing and
improving these sophisticated tools, which
manage the full simulation chain - this starts
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with an in-depth knowledge of acoustic
materials behaviour, goes on through these
materials being modeled into components, and
culminates in the simulation of full vehicles.
Sound Engineering
So how do we deal with the noise once we
have analysed, simulated, and measured
it? By designing vehicles to reduce noise,
vibration, and harshness and by equipping
them with noise control components such
as under engine shields, hoodliners, inner
dashes, and carpet systems. Acoustic properties
are engineered into these components and
are tuned to reduce the noise from engines
and tyres inside the vehicle via damping,
insulation, and absorption. But at the same
time cars have to be lighter, as this affects fuel
consumption, their efficiency, and ultimately
the environment. New technologies and hightech
materials come into play when these
components are designed and manufactured to
be highly efficient and extremely lightweight.
It is not simply a question of filling the
car with absorption materials; the quality
of sound and not just the quantity make a
difference. The car should be well insulated
but not all the sound should be absorbed, as
each car typology and brand also has its own
identifying sound – it is part of its appeal
and must be carefully safeguarded. Here the
current trend is all about subjective acoustics.
Subjective Acoustics
"How can I reduce the sound pressure level
at the driver's ear by 3dB and at the same
time decrease the overall weight of the
acoustic package by 5 kg?" This question
illustrates a typical concern of automotive
engineers designing sound packages.
But automotive acoustic designers have
recently discovered that 'quieter' does not
necessarily coincide with 'more pleasant';
analysis of acoustic signals alone is not
sufficient to identify the level of 'sound
quality' inside a car. In addition to the quest
for silence, weight, and cost reduction,
the concept of 'sound quality design' has
Main Topic | Automotive | Current Issues
Jean-Charles Bonnet
Head of Acoustics Laboratory
Rieter Automotive China

Main Topic | Automotive | Current Issues
The car should
be well
insulated but
not all the
sound should
be absorbed,
as each car
typology and
brand also
has its own
identifying
sound.
gained importance. Initially, sound quality
design starts by identifying the attractive
sound attributes from unpleasant ones.
From this knowledge, the target sound is
elaborated. Instead of classical acoustic tools
and methodologies, the engineer relies on
Psychoacoustics and Subjective Acoustics.
Psychoacoustics
Known as 'the science of the hearing
system as a receiver of acoustical
information', psychoacoustics uses various
metrics to develop quantitative correlations
between acoustical stimuli and the hearing
sensation. Examples of these metrics are:

Acoustics in China
In the past, vehicle acoustics did not play as
important a role in Chinese car production.
There are a number of reasons for this: