Chapter 6: Impedance measurements
Chapter 6: Impedance measurements
Chapter 6: Impedance measurements
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Acoustic impedance <strong>measurements</strong><br />
Movement in the resonator (z-axis)<br />
Next the probe is moved in the z direction from inside the tube<br />
(z=-14mm) to the surface of the plate (z=0 mm) and further to above the<br />
plate (z=6mm), see below.<br />
Normalised autospectrum Pressure<br />
Autospectrum [ dB ]<br />
40<br />
20<br />
0<br />
-20<br />
-40<br />
z = -14mm<br />
z = -6mm<br />
z = 0mm<br />
z = 2mm<br />
z = 6mm<br />
1000 1330 10000<br />
Frequency [ Hz ]<br />
Normalised autospectrum Velocity<br />
Autospectrum [ dB ]<br />
40<br />
20<br />
0<br />
-20<br />
-40<br />
z = -14mm<br />
z = -6mm<br />
z = 0mm<br />
z = 2mm<br />
z = 6mm<br />
40<br />
1000 1330 10000<br />
Frequency [ Hz ]<br />
<strong>Impedance</strong> ( Magnitude )<br />
abs Z [ Pa/(m/s) ]<br />
20<br />
0<br />
-20<br />
z = -14mm<br />
z = -6mm<br />
z = 0mm<br />
z = 2mm<br />
z = 6mm<br />
-40<br />
1000 1330 10000<br />
Frequency [ Hz ]<br />
<strong>Impedance</strong> ( Phase )<br />
180<br />
phase Z [ degrees ]<br />
90<br />
0<br />
-90<br />
-180<br />
1000 1330 10000<br />
Frequency [ Hz ]<br />
z = -14mm<br />
z = -6mm<br />
z = 0mm<br />
z = 2mm<br />
z = 6mm<br />
Fig. 6.55: Autospectrum and impedance along the z-axis (in and out the tube).<br />
6-49
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