development and integration of sound modules

DE VELO PMENT Ac oustic s | N V H
DEVELOPMENT AND INTEGRATION
OF SOUND MODULES
Electric mobility presents a whole range of new challenges for developers. One aspect is vehicle acoustics.
As there is no noise being produced by an internal combustion engine, tyre noise and wind noise become
more dominant. The challenge is to evaluate and to design the new sounds of an electric vehicle. Development
specialist Bertrandt supports its customers in developing sound modules and integrating them into electric
vehicles.
16
NEW SOUND THROUGH
ENVIRONMENTALLY FRIENDLY
MOBILIT Y
AUTHOR
integration requirements, the engineers
are also considering new technical
methods.
The sound of an electric vehicle is quite
different from the familiar sound of
conventional cars. There is no longer
the dominant sound of an internal combustion engine. What is more, secondary noise that was previously largely
masked by other noise becomes more
noticeable and is therefore often perceived as irritating. As a result, this creates an unfamiliar impression that may
also be unsettling for the driver, for
example when the vehicle does not provide any vibro-acoustic feedback on
startup and the driver is unable to tell
whether the engine is running or not.
However, the focus is not only on the
interior. Exterior noise also changes
and must be developed in a targeted
manner with regard to safety aspects.
For that reason, there is now much
greater emphasis on evaluating and
designing the new sounds of an electric
vehicle. In addition, there is the question of how sounds can be produced
that may emotionally inspire the customers of the future. To resolve this
challenge, Bertrandt supports its customers in developing sound modules
and integrating them into electric vehicles, 1. In addition to development and
DIPL.-ING. MARC MÄNDL
is Team Leader Acoustics at
Bertrandt in Ingolstadt (Germany).
Material
INDIVIDUAL CONDITIONING AS AN
INFLUENCING FACTOR
The aim of targeted sound design is to generate the customer’s emotional enthusiasm
for the product. Many different influences
are involved here. Firstly, every person is
individually conditioned based on their
experience. This conditioning means that
there is no clear characterisation of people
for a corresponding sound.
Secondly, potential customers have
individual expectations towards a product. These can range from identification
and enthusiasm to the general rejection
of or even contempt for a particular
brand. In this case, we speak of the orientation of a brand or a product towards
a target group.
Almost all manufacturers are currently
extending their product range, whether it
is with new models or with subsidiary
brands that cover niches that have not
previously been occupied and which are
aimed at acquiring new customers. This
means that, also when it comes to acoustics, a wide portfolio of different sound
backgrounds is required in order to individually appeal to as many customers as
possible.
Method
Airborne/str.-borne transmission
Branding target group
Integration of background sound
Lightweight design measures
Objectification – stat. methods
Passive/active excitation
Material
Insulation/damping/absorption
Exterior and interior noise
Expert knowledge in sound design
Psychology/psychoacoustics
Masking
Opt. methods
Energy
Actuators:
piezo/loudspeakers/shakers/resonators
Operating point/application ranges
Vehicle
Hearing
Enthusiasm/rejection
Interference/environmental influences
Measuring sensors
Production technology
Expectations (price/performance)
Experience/conditioning
Target/Result
Emotionally exciting
and harmonious
sound for
electric
vehicles
Emotion
Experts
Active systems
Machine
Human
being
1Process Ishikawa – analysis of factors influencing target achievement
07-08I2014 Volume 116
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DE VELO PMENT Ac oustic s | N V H
New powertrain concepts are now being
added to the conventional ones. In the
current trend of environmentally
friendly mobility, electric vehicles present new challenges for broad areas of
vehicle development. For example, electric vehicles no longer have the dominant sound source that has characterised
our perception of vehicle sound ever
since cars were invented, 2.
We therefore need to examine where
the main challenges in vehicle acoustics
lie today. We need to analyse which
components of a vehicle’s acoustic background will no longer exist in the future
and which ones will become dominant.
Not every sound in a vehicle can be
planned. Many components of technically natural sound are annoying from
an acoustic perspective. This situation is
the result of many requirements that
need to be met by the vehicle. One
example is lightweight design, which has
been very successful in changing the
basic structure of vehicles in recent
years and has had a positive influence on
their fuel efficiency. Minimising weight
is of key significance in electric vehicles
in particular, as a lightweight vehicle
can achieve a greater driving range than
a heavy one. A limited driving range is
currently a functional disadvantage of
electric vehicles compared to those with
an internal combustion engine. A lightweight diesel vehicle and an economic
driving style can significantly reduce
fuel consumption, and the customer
does not have to accept restrictions of
driving range.
Against this background, the situation for acoustics becomes much more
relevant. Stiffer materials are now being
used and these radiate more energy. The
reduced masses, on the other hand,
have less system attenuation. In a
weight-optimised vehicle in which more
expensive materials are used, weightintensive passive-acoustic measures are
avoided.
Weight-optimised body structures that
are similar to framework and perforated
structures produce excellent results.
However, for acoustic engineers, these
systems are becoming more and more
challenging to manage, as they offer
many different paths for airborne and
structure-borne sound. Each of these
18
100
Load change noise
AS (= airborne sound)
> 1.5 kHz
75
Engine load [%]
NEW CHALLENGES DUE TO
ELECTRIC MOBILIT Y
Mechanical
engine noise
AS
< 2 kHz
Gas and mass forces
Engine mounts
StS
(= structure-borne sound)
< 1 kHz
50
Wind noise
AS
> 1.5 kHz
25
Rolling noise
StS AS
Tyres < 1400 Hz
Humming approx. 30 Hz
0
0
50
Driving speed [km/h]
100
150
2Composition of the most important noise components in a vehicle
paths has its own characteristic and
must be evaluated and, if necessary,
optimised with regard to sound insulation and damping.
One example of such changes is the
bulkhead. This sheet steel structure
separates the engine compartment from
the vehicle interior and represents the
most important level of sound insulation between what is currently the dominant sound source and the sensitive
receiver. Today, this barrier is more or
less permeable, with holes for different
systems such as the steering column,
air conditioning lines, electric cables,
etc. The resulting weak points require
complex measures to rectify their
acoustics.
Improvements in the core functions of
the vehicle result in many new and
annoying sounds. Added to these are the
sounds that make up the general background sound of the vehicle. In addition
to the engine, transmission, tyre, intake,
exhaust and wind noise, many noises
are also caused by auxiliary units such
as heating/air conditioning or seat comfort systems. In addition, the background
sound is influenced by external noise.
Wind noise in particular is perceived by
customers in a completely different way.
Subjectively, they have the impression of
driving against a wall of wind.
A designed sound should take all of
these factors into consideration and must
not be so loud that it dominates percep-
tion. For that reason, the subject of
sound design is currently very popular.
It occupies a small niche in the field of
vehicle acoustics that is becoming
increasingly more important.
This niche requires experts that are
characterised by various attributes.
Firstly, they must have distinct acoustic
taste. This may be the result, for example, of a strong musical and instrumental
affinity. This facet is completed by a concept of the effect that the product is to
have on the customer.
It is interesting to compare vehicle
sound and music. The perception of
music is very much influenced by our
mood, for example by how we feel at a
certain time. Vehicle sound must therefore not become a distraction when we
drive, as we are not able to switch off the
sound if we are not currently in the right
mood. An exciting alternative would be
to design the sound in accordance with
the customer’s driving style. For example, a calming vehicle sound could have
a positive effect on an aggressive driving
style. Whether such an influence is possible or desirable is a matter for further
consideration.
Secondly, the experts must have a
technical understanding of the systems
and of the vehicle as a complete product.
This profile is rounded off by expertise
in measuring technology, actuators and
expert tools for generating sounds that
produce the right results when superim-
posed on the vehicle’s own background
noise. This result must also be achieved
not only at one operating point but also
in all possible application areas of the
vehicle.
When it comes to designing a sound,
the focus is on the expert. Like an artist, the expert incorporates his own
taste, thus designing several different
suggestions that he considers to be harmonious. These are then tested by him
in the vehicle until an optimum result is
achieved. Afterwards, the sounds are
then applied to real vehicles, where they
have to convince the decision-makers.
The use of objectification methods
does not only produce limited results
here. If several test persons are analysed in order to derive a generally
applicable sound that is liked by as
many people as possible, the result
could possibly only be a mediocre
sound without any character. Such a
sound would not inspire any emotions
among customers.
The desired vehicle sound can be realised through two methods. An existing
sound source can be passively manipulated such that a better sound character is
achieved (for instance using resonators
for airborne noise). An active method
asks for more effort and requires the use
of sensors, actuators and controllers.
These can react to operating cycles or in
real time to the instantaneous background noise. Such methods are
described as Active Noise Control (ANC).
The actuators can be loudspeakers (for
airborne sound, AS), electrodynamic
shakers or piezo actuators for structureborne sound (StS).
3Location of sound sources for rolling noise
07-08I2014 Volume 116
BACKGROUND SOUND IN
ELECTRIC VEHICLES
As the entire characteristic of the internal combustion engine no longer exists,
it must be replaced by a new characteristic. As far as this is concerned, opinions
range from no sound at all in order to
reduce noise pollution in everyday life to
a synthetic combustion noise that takes
account of conventional expectations.
As in the case of acoustics, two different
requirements also come into conflict in
this case too. The driver requires feedback
on the operating point in order to react
correctly to different situations. Pedestrians often use their sense of hearing to
detect an approaching vehicle. In the case
of an electric vehicle, they are able to do
this only if the vehicle’s speed is above
approximately 40 km/h, 3. Below this
speed, the vehicle is virtually silent. At a
higher speed, tyre noise becomes perceivable. However, in this case, the vehicle will
very quickly reach the pedestrian, who
may no longer have sufficient time to react
to avoid a dangerous situation.
The new sound components that the
electric motor itself generates cannot be
completely neglected. Although these are
much quieter than combustion noises,
they have many high-frequency components to which human beings are much
more sensitive.
SOLUTIONS ON THE MARKET
At the present time, the automotive industry is not pursuing one distinct strategy in
particular. The safety-relevant requirements are likely to be fulfilled by generat-
ing a sound similar to that of the internal
combustion engine, while at the same time
designing the direction in which it is radiated. The sound can be directed towards
the pedestrian and only needs to be loud
enough to warn the pedestrian, after which
the sound level can be reduced again.
These sounds can be generated either by
using in some cases newly developed loudspeaker concepts, 4, or by a combination
of an actuator with an existing component,
which acts as a membrane.
Several solutions are possible for the
interior. There are basically two main
approaches: sounds that are based on
audio effects from science fiction or computer games and those that re-create a
familiar setting. Generally speaking, the
synthetic sounds are somewhat exaggerated. The aim is to make the image of the
new powertrain concepts a positive one.
OUTLOOK
Electric vehicles represent a major challenge for acoustics development. There is a
need for experts who can react to the
change that is now taking place in the
automotive industry – the greatest change
in acoustics since the development of the
modern car. The specialists are called
upon to design something new. These initial solutions represent the very first concepts for the next generation of customers.
It might even be interesting if the design
process involves not only experts but also
others, such as young people. This might
create additional incentives and differentiation from other products. The idea is to
create the automotive sound of the future
for the car buyers of the future.
4Characteristic of sound radiation for rolling noise
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