Utilizing Statistical Energy Analysis for Optimizing a Vehcile Sound Package

1. 03NVC-172
SEA for Design: A Case Study
Allan C. Aubert
Roush Industries, Inc.
John T. Long
Ford Motor Company
Mark J. Moeller
MUG, llc.
Robert E. Powell
Ford Motor Company
Copyright © 2003 Society of Automotive Engineers, Inc
would neglect structural forcing inputs. These were to
ABSTRACT
be handled by other analytical efforts, using other
methods. The primary forcing cases investigated were
This paper reports on a case study involving the use of
due to tire / road noise, and the team would only
SEA methods in the acoustic design of an advanced
address tailpipe and engine compartment noise as a
design luxury sedan. The power of the analytical
second priority. The tire noise case used in the reported
method was used to advantage in a case of a vehicle
results involved inputs from all four wheel areas, and
with very challenging NVH targets. Three practical
was derived from data taken at 45 mph on a smooth test
issues are highlighted; review of a method to handle
track.
adding components that contribute acoustic absorption,
presentation of data to aid vehicle content decisions,
Response location priority was focused on the driver’s
and design sensitivity analysis. This effort demonstrates
head space, followed by front and rear passenger head
an example in which SEA modeling provided relevant
spaces.
and timely input to the vehicle design team to aid
decision making for sound package content.
This paper reports on three techniques which were
found to improve the usefulness, ease of model
INTRODUCTION
preparation and timeliness of the SEA results in their
benefit to the decision makers of the vehicle sound
An advanced design vehicle development effort was
package design team.
undertaken, the NVH design goal being to develop a
prototype luxury sedan with properties that would be as
PRESENTATION OF SEA RESULTS
good as, or better than the Best in World. Untraditional
approaches to achieve this result were allowed, in an
PRIORITIZATION OF SOUND PACKAGE CONTENT
effort to discover what technologies needed to improve
in this highly competitive market. The challenges to
The design team began work starting from a recent
improve performance for road noise were seen to be
model year, production luxury sedan. The SEA model
some of the greatest in this effort. Consequently, a
team was able to obtain an SEA model which was
team was assembled which attacked these issues using
nearly representative of this vehicle. Brief early effort
both experimental and Statistical Energy Analysis (SEA)
was focused to bring the baseline SEA model into
methods [1-7]. For several manufacturers, it is not
correlation with the baseline development vehicle.
common to rely heavily on SEA at an early enough
Targets were set which required extensive improvement
stage to have its results give practical design guidance.
in the road noise performance of the vehicle.
This effort was accelerated and focused in its direction
to make the highest priority be to support design team
Previous modeling efforts would present results in terms
decision-making.
of the improvement in response that a candidate
modification would produce as compared to the
At an early stage, it was decided that the SEA modeling
baseline. Because of the drastic changes envisioned,
would address acoustic forcing and response only, and

2. the SEA team realized that this method of assessing the degrade the final vehicle performance by 3 dB in the
effectiveness of treatments would not lead to the correct high frequency range. Next in importance is under body
conclusions as to whether treatments were needed in treatments. In Figure 2, for engine noise inputs, to
order to meet the final targets. A treatment could be remove hush panels from the design would raise the
shown as ineffective in the baseline vehicle, and yet noise levels in the mid- and high frequency ranges by
become very effective when other treatments had 3 dB. Cabin absorption is the next most crucial design
changed the balance of acoustic power flow in the change for this noise source. Since hush panels work to
system. seal the dash and instrument panel space, it is
reasonable that they are a significant contributor to
cabin noise attenuation in a well-treated vehicle for the
Advanced Design Luxury Sedan SEA Results
Cabin Absorption
engine noise case. However, this result quantified for
45 MPH Tire Noise Ranking of Treatments
Under Body Treatment
Amount Design Performance is Degraded
the vehicle design team the importance of these panels.
Hush Panels
by Switch of Component to Baseline Treatment
Earlier data derived from adding them to a baseline
Laminated Side Glass
Laminated Steel
vehicle indicated that they added very little to cabin
Engine Compartment Absorption
noise performance. However, the SEA team’s
Trunk Absorption
dB Change in Driver's Head Space
conclusion was that the energy flow path treated by the
Tunnel Liner
hush panels had become dominant because other
3.0
treatments found in the fully treated vehicle had reduced
2.5
Cabin Absorption
2.0
the dominant paths of the baseline vehicle.
Under Body Treatment
1.5
Hush Panels
Laminated Side Glass 1.0
BOOK KEEPING OF ACOUSTIC ABSORPTION
Treatment Laminated Steel
0.5
Engine Compartment Absorption
0.0
Trunk Absorption
Acoustic absorption was seen to be at or near the top in
2000 -
Tunnel Liner 5000
1000 -
Figure 1: Tire Noise Pareto
importance, among all treatments for the acoustic
1600
100 -
800 Frequency (Hz)
performance of the vehicle, in all the load cases
A bar chart “pareto” approach was chosen to present investigated. The SEA team discovered that proper
model results to the vehicle design team. This tracking of sources of acoustic absorption, and
approach would display results of a “Max Pack” vehicle, assignment of the absorption to the correct acoustic
or one which had installed in the SEA model the most spaces, was a serious issue for a complex SEA model.
effective treatments which were envisioned for the final A book keeping method is needed for this tracking which
vehicle. Then the pareto would show the penalty in final allows a straightforward way to assign absorption from
vehicle performance experienced by choosing to not new treatments applied in a design change. This is an
include that treatment in the final sound package design. area of SEA modeling which commonly leads to input
This approach takes advantage of the unique feature of errors. Though the authors realize that this is not a
SEA modeling, that sweeping design changes can be completely new concept [8], the method chosen to track
rapidly made to an SEA model because of the relatively absorption is here presented.
small amount of information in the model as compared
to FEA or other methods.
Sample Absorption Spreadsheet
Trunk Absorption
Advanced Design Luxury Sedan SEA Results
Engine Noise Ranking of Treatments Laminated Side Glass
Engine Compartment Rear Driver's Side
Amount Design Performance is Degraded Laminated Steel
by switch of Component to Baseline Treatment
Subsystem ID# 10087
Tunnel Liner
Under Body Treatment
Material ID# 1187
Engine Compartment Absorption
dB Change in Driver's Head Space
Passenger Compartment Absorption
Treatment=> Added Measured Added New Total
Hush Panels
Hood liner Engine Dash Liner Absorption
Compartment Area:
3.0
Absorption
2.5 Hush Panels
Absorption 2.55E+05 2.87E+05 7.00E+04 6.12E+05
2.0 Passenger Compartment Absorption
Area =
Engine Compartment Absorption
1.5
Under Body Treatment
Frequency Alpha Values New Alpha:
1.0
Tunnel Liner
0.5
125 0.041 0.3100 0.0210 0.165
Laminated Steel
0.0
Treatment
Laminated Side Glass
250 0.094 0.3100 0.0750 0.193
2000 -
10000 Trunk Absorption
1000 -
500 0.180 0.3100 0.2130 0.245
Frequency (Hz) 1600
100 -
Figure 2: Engine Noise Pareto
800
1000 0.383 0.6800 0.4180 0.526
2000 0.805 0.7600 0.6020 0.761
Figures 1 and 2 show the final pareto charts for the tire
4000 0.948 0.8800 0.7780 0.897
noise and engine noise cases.
8000 0.924 0.9050 0.8570 0.907
Table 1: Absorption Tracking
In the Figure 1, for tire noise inputs, the pareto chart
says that a design decision which leaves the acoustic
absorption of the cabin at the baseline levels would