How to assess walking sound at
32 Hz
Arnold Koopman
Sven Lentzen
Ton van Noort
What?
• Light weight buildings are typically vulnerable below 100 Hz
• Assessment methods are available down to 63 Hz
• But we probably need to go even deeper down: 32 Hz
• One big issue is contact noise, from footsteps
• But how to assess contact noise insulation at 32 Hz?
• In light weight buildings one expects floor-body interaction
• Which assessment method takes that sufficiently into account?
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Contents
• Overview of contemplated assessment methods
• Methodology
• Measurement results
• Conclusion
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Assessment methods
Tapping machine
• Used for ‘high frequency’ contact noise
• But isn’t it too ‘light’ for low frequencies?
Impact ball
• Standard ball dropped from standard height
• Designed for low frequencies
Footfall vibration method
• Measured pulse-response convoluted with library of foot steps
• Designed for 1-50 Hz
• Designed for vibration
• Just replace accelerometer by microphone
• But still a complex method
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Methodology
• We assume that footfall vibration method gives the most realistic
results
• Actual footsteps being used
• Measurement includes floor-body interaction
• But we don’t want it as a standard method
• We use it as the reference standard
• We compare the two other methods with that reference standard
• Can we stick with the tapping machine, or do we need the ball?
• Criterium: interaction
• measurements on light floor and heavy floor
• difference in sound power level should be equal to that found
with footfall method
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Measurement results
In the following order:
• Sound pressure levels on a timber floor, per method
• Sound pressure levels on a concrete floor, per method
• Difference between floors per method
3 different excitation points, 13 reception points
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Timber floor
Heeldrop
Impact ball
Tapping machine
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31,5 Hz
125 Hz
31,5 Hz
125 Hz
31,5 Hz
125 Hz
Concrete floor
Heeldrop
Impact ball
Tapping machine
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31,5 Hz
125 Hz
31,5 Hz
125 Hz
31,5 Hz
125 Hz
Difference between floors
Heel-Ball
Heel-Tap
Ball-Tap
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31,5 Hz
125 Hz
31,5 Hz
125 Hz
31,5 Hz
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125 Hz
Measurement results
Looking at 31,5 third octave band, side position
Concrete  timber:
• Heeldrop: 50/60  70/80, 20 dB increase
• Impact ball: 65/75  80/90, 15 dB increase
• Tapping machine: 65/75  70/80, 5 dB increase
• So impact ball is much closer to heeldrop
• Tapping machine underestimates sound level increase from
concrete to timber
• In a linear world: interaction would cause higher input power for
lower impedance differences, which could explain the observed
differences in increase
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Conclusions
Given the heeldrop assessment method, from footfall vibration, as
reference standard,
at 32 Hz,
the impact ball is significantly more representative for walking
noise than the tapping machine
as the tapping machine underestimates the increase in source
level with decreasing floor impedance
So let’s buy those balls!
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