| Page 1 25.01.2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential...
-
Upload
isaac-kent -
Category
Documents
-
view
213 -
download
0
Transcript of | Page 1 25.01.2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential...
|| Page Page 1125.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
Boundary conditionsBoundary conditions
The external surface of the solid model need to be The external surface of the solid model need to be surround by proper boundary conditionssurround by proper boundary conditions
The sound sources (loudspeakers) were modeled The sound sources (loudspeakers) were modeled as areas where the normal acceleration is known as areas where the normal acceleration is known as a function of frequencyas a function of frequency
The internal surfaces of the car are modeled as The internal surfaces of the car are modeled as sourfaces of known complex acoustical sourfaces of known complex acoustical impedence as a function of frequencyimpedence as a function of frequency
Some surfaces were modeled as rigid walls Some surfaces were modeled as rigid walls (glass, steel parts not covered by sound (glass, steel parts not covered by sound absorbing materials)absorbing materials)
The values of acceleration and impedance were The values of acceleration and impedance were measured “in situ” thanks to novel hardware and measured “in situ” thanks to novel hardware and software toolssoftware tools
|| Page Page 2225.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
Reference measurements in the carReference measurements in the car
Hardware: PC and audio interface
Edirol FA-101
Firewire sound card:
10 in / 10 out
24 bit, 192 kHz
ASIO and WMA
|| Page Page 3325.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
Reference measurements in the carReference measurements in the car
Software
Aurora Plugins
Generate SweepGenerate Sweep
Convolution / DeconvolutionConvolution / Deconvolution
Impulse Response extractionImpulse Response extraction
Cross FunctionsCross Functions
|| Page Page 4425.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
Measurement process
The desidered result is the linear impulse response of the acoustic propagation h(t). It can be recovered by knowing the test signal x(t) and the measured system output y(t). It is necessary to exclude the effect of the not-linear part K and of the background noise n(t).
Not-linear, time variant
system K[x(t)]
Noise n(t)
input x(t) +
output y(t) linear system w(t)h(t)
distorted signal w(t)
|| Page Page 5525.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
Test signal: Log Sine Sweep
x(t) is a sine signal, which frequency is varied exponentially with time, starting at f1 and ending at f2.
1e
f
fln
Tf2sin)t(x 1
2
f
fln
T
t
1
2
1
|| Page Page 6625.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
Test Signal – x(t)
|| Page Page 7725.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
Deconvolution of Log Sine Sweep
The “time reversal mirror” technique is employed: the system’s impulse response is obtained by convolving the measured signal y(t) with the time-reversal of the test signal x(-t). As the log sine sweep does not have a “white” spectrum, proper equalization is required
Test Signal x(t) Inverse Filter z(t)
|| Page Page 8825.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
Measured signal - y(t)
The not-linear behaviour of the loudspeaker causes many The not-linear behaviour of the loudspeaker causes many harmonics to appearharmonics to appear
|| Page Page 9925.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
Inverse Filter – z(t)
The deconvolution of the IR is obtained convolving the measured The deconvolution of the IR is obtained convolving the measured signal y(t) with the inverse filter z(t) [equalized, time-reversed x(t)]signal y(t) with the inverse filter z(t) [equalized, time-reversed x(t)]
|| Page Page 101025.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
Result of the deconvolution
The last impulse response is the linear one, the preceding are the harmonics distortion products of various orders
1°2°3°
5°
|| Page Page 111125.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
Maximum Lenght Sequence vs. Sweep
|| Page Page 121225.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
In-situ measurement of the acoustical propertiesIn-situ measurement of the acoustical properties
The measurement of the acoustical impedance is performed employing a The measurement of the acoustical impedance is performed employing a Microflown pressure-velocity probeMicroflown pressure-velocity probe
|| Page Page 131325.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
In-situ measurement of the acoustical propertiesIn-situ measurement of the acoustical properties
The probe needs to be calibrated for proper gain and phase matching at The probe needs to be calibrated for proper gain and phase matching at low frequencylow frequency
Calibration over a reflecting surfaceCalibration over a reflecting surface Free-Field calibrationFree-Field calibration
|| Page Page 141425.01.200725.01.2007 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential
In-situ measurement of the acoustical propertiesIn-situ measurement of the acoustical properties
A specific software (Aurora plugin) has been developed for speeding up A specific software (Aurora plugin) has been developed for speeding up both calibration and measurement of the acoustical properties with the new both calibration and measurement of the acoustical properties with the new pressure-velocity probe techniquepressure-velocity probe technique
Input parametersInput parameters ResultsResults