Microflown Calibration

1

• Microflown Calibration
• Microflown Technologies
• The Netherlands
• www.microflown.com

2

• Contents
• Short standing wave tube
• Piston in a sphere high frequency
• Piston in a sphere low frequency
• Calibration file

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Short standing wave tube
4
Standard response
5
fp , fu
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Correction
7
Corrected response
8
Phase reponse
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Correction

• Phase in tube is 90 degrees

10
Corrected phase response
11
Piston in a sphere

• Free field
• Known impedance
• Measure pressure with reference microphone
• Calculate particle velocity out pressure and
  known impedance

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principle
13
Set up
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Impedance
Impedance similar as point source
15
Pressure response


16
Typical velocity response
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Low frequencies

• Source does not emit low frequency pressure
• Background noise pressure is dominant
• Impedance is not defined at low frequencies
• Velocity cannot be calculated out impedance
• Pressure can be calibrated 20Hz-20kHz

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Low frequency sphere calibration
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• Sound pressure in the sphere is related to
  loudspeaker motion
• Particle velocity in front of sphere is related
  to loudspeaker motion
• So sound pressure in sphere is realted to
  velocity in front of the sphere

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Set up
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model
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Typical response
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conclusion

• SWT
• Good in noisy environment
• Good in small environment
• Easy to use
• Somewhat limited bandwidth (40Hz-3.5kHz)
• Sphere
• Full bandwidth
• Requires two measurements for full bandwidth
• Requires somewhat large room
• Better in not so noisy environment