Boundary conditions The external surface of the solid

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 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) § The values of acceleration and impedance were measured “in situ” thanks to novel hardware and software tools 25. 01. 2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential | Page 1

Reference measurements in the car Hardware: PC and audio interface Edirol FA-101 Firewire sound card: 10 in / 10 out 24 bit, 192 k. Hz ASIO and WMA 25. 01. 2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential | Page 2

Reference measurements in the car Software Aurora Plugins Generate Sweep Convolution / Deconvolution Impulse Response extraction Cross Functions 25. 01. 2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential | Page 3

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). 25. 01. 2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential | Page 4

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. 25. 01. 2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential | Page 5

Test Signal – x(t) 25. 01. 2007 Angelo Farina UNIPR / ASK Industries |

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) 25. 01. 2007 Angelo Farina Inverse Filter z(t) UNIPR / ASK Industries | All Rights Reserved | Confidential | Page 7

Measured signal - y(t) v. The not-linear behaviour of the loudspeaker causes many harmonics

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)] 25. 01. 2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential | Page 9

Result of the deconvolution 5° 3° 2° 1° The last impulse response is the linear one, the preceding are the harmonics distortion products of various orders 25. 01. 2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential | Page 10

Maximum Lenght Sequence vs. Sweep 25. 01. 2007 Angelo Farina UNIPR / ASK Industries

In-situ measurement of the acoustical properties § The measurement of the acoustical impedance is performed employing a Microflown pressure-velocity probe 25. 01. 2007 Angelo Farina UNIPR / ASK Industries | All Rights Reserved | Confidential | Page 12

In-situ measurement of the acoustical properties § The probe needs to be calibrated for proper gain and phase matching at low frequency Calibration over a reflecting surface 25. 01. 2007 Angelo Farina Free-Field calibration UNIPR / ASK Industries | All Rights Reserved | Confidential | Page 13

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 Input parameters 25. 01. 2007 Angelo Farina Results UNIPR / ASK Industries | All Rights Reserved | Confidential | Page 14