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| Page 1 25.01.2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential Boundary conditions The external surface of the solid model.

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Presentation on theme: "| Page 1 25.01.2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential Boundary conditions The external surface of the solid model."— Presentation transcript:

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2 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential Boundary conditions The external surface of the solid model need to be surround by proper boundary conditions The external surface of the solid model need to be surround by proper boundary conditions The sound sources (loudspeakers) were modeled as areas where the normal acceleration is known as a function of frequency The sound sources (loudspeakers) were modeled as areas where the normal acceleration is known as a function of frequency The internal surfaces of the car are modeled as sourfaces of known complex acoustical impedence as a function of frequency The internal surfaces of the car are modeled as sourfaces of known complex acoustical impedence as a function of frequency Some surfaces were modeled as rigid walls (glass, steel parts not covered by sound absorbing materials) Some surfaces were modeled as rigid walls (glass, steel parts not covered by sound absorbing materials) The values of acceleration and impedance were measured in situ thanks to novel hardware and software tools The values of acceleration and impedance were measured in situ thanks to novel hardware and software tools

3 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential Reference 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

4 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential Reference measurements in the car Software Aurora Plugins Generate Sweep Convolution / Deconvolution Impulse Response extraction Cross Functions

5 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential 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).

6 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential Test signal: Log Sine Sweep x(t) is a sine signal, which frequency is varied exponentially with time, starting at f 1 and ending at f 2.

7 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential Test Signal – x(t)

8 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential Deconvolution of Log Sine Sweep The time reversal mirror technique is employed: the systems 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)

9 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential Measured signal - y(t) The not-linear behaviour of the loudspeaker causes many harmonics to appear The not-linear behaviour of the loudspeaker causes many harmonics to appear

10 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential Inverse Filter – z(t) The deconvolution of the IR is obtained convolving the measured signal y(t) with the inverse filter z(t) [equalized, time-reversed x(t)]

11 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential 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°

12 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential Maximum Lenght Sequence vs. Sweep

13 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential In-situ measurement of the acoustical properties The measurement of the acoustical impedance is performed employing a Microflown pressure-velocity probe The measurement of the acoustical impedance is performed employing a Microflown pressure-velocity probe

14 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential In-situ measurement of the acoustical properties The probe needs to be calibrated for proper gain and phase matching at low frequency The probe needs to be calibrated for proper gain and phase matching at low frequency Calibration over a reflecting surface Free-Field calibration

15 | Page Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential In-situ measurement of the acoustical properties A specific software (Aurora plugin) has been developed for speeding up both calibration and measurement of the acoustical properties with the new pressure-velocity probe technique A specific software (Aurora plugin) has been developed for speeding up both calibration and measurement of the acoustical properties with the new pressure-velocity probe technique Input parameters Results


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