Chaparral Physics Research Jay Helmericks Duncan Marriott John

Chaparral Physics Research ▫ Jay Helmericks, Duncan Marriott, John Olson ▫ Wilson Infrasound Observatories ▫ Geophysical Institute, University of Alaska Fairbanks Presented at the Infrasound Technology Workshop Bermuda 3 Nov 2008 This presentation does not necessarily reflect the policies or views of the United States Government.

Abstract This talk will cover two areas of research that Chaparral Physics has been pursuing, both of which are of interest to the general Infrasound community. The first is an investigation of the linearity of Chaparral Physics sensors. The testing shows that there are three regions: with small-amplitude signals the sensor is fully linear; then, as the signal amplitude increases, there is a point where the linearity of the sensor depends on the shape of the incoming wave; and finally, as the signal exceeds 150 Pa peak-to-peak the sensor response completely departs from linearity. The second area of research looks at both the effectiveness and frequency response of wind noise reduction systems, from ~5 Hz to 100 Hz. The effectiveness of wind noise reduction systems have been studied extensively, but little work has been done on the frequency response of such the systems. Preliminary results from this research will be presented. CP Research • ITW 2008 2

Introduction ▫ Linearity of Chaparral Physics sensors ▫ Frequency response of soaker hose ▫ Large area vs small area wind noise reduction systems ▫ New Chaparral Physics sensors CP Research • ITW 2008 3

Linearity Setup ▫ Constructed a test chamber with heavy plywood with a subwoofer as the signal source ▫ Standard audio power amplifier and sound card to drive the speaker ▫ Pressure reference was a G. R. A. S 40 BF ¼” microphone ▫ Able to test from 1 to ~ 200 Hz, and 0. 5 Pa p -p to 700 Pa p-p CP Research • ITW 2008 4

Test Chamber CP Research • ITW 2008 5

Test chamber opened CP Research • ITW 2008 6

Single Tone Test ▫ Drove the chamber with a sine wave of varying frequency and amplitudes ▫ Compared the output of the G. R. A. S. microphone to the Chaparral microphones CP Research • ITW 2008 7

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100 Pa Fit CP Research • ITW 2008 9

20 Pa Fit CP Research • ITW 2008 10

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Linearity to 650 Pa p-p CP Research • ITW 2008 12

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Two Tone Test ▫ Used the same test setup ▫ Ran two sine tones at the same time ▫ A low frequency tone is varied in amplitude ▫ A high frequency tone is constant through the tests ▫ Looked at the amplitude of the high frequency tone as the low frequency tone moves the diaphragm through its operating range CP Research • ITW 2008 14

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Linearity Summary ▫ Below 20 Pa p-p non-linearity is not significant ▫ From 20 -150 Pa p-p small scale nonlinearity needs to be considered ▫ Above 150 Pa the wave shape will have significant distortion CP Research • ITW 2008 18

Response of Wind Noise Filters ▫ Measured the frequency response and the noise reduction ▫ 4 50 ft soaker hoses ▫ 2 3 ft soaker hoses ▫ Foam doughnut ▫ Used the same signal source as the linearity tests CP Research • ITW 2008 19

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Freq Response CP Research • ITW 2008 23

Wind Noise Reduction CP Research • ITW 2008 24

Wind Filter Summary ▫ Short soaker hoses provide no noise reduction and significantly attenuate high frequency signals ▫ Long soaker hoses provided good noise reduction with a slight attenuation of high frequency signals ▫ There appears to be no wind noise reduction relative to an open sensor with a filter that does not have significant averaging area CP Research • ITW 2008 25

New Sensors ▫ Added a single port configuration back to the lineup ▫ Lighter weight ▫ Provides an option when a manifold is not needed ▫ New feature reduced low cost sensor for 30% less then a M 25 ▫ Removed gain selection and sensor self-check functions ▫ See website for details (soon) ▫ www. chaparral. gi. alaska. edu CP Research • ITW 2008 26

Conclusion ▫ Linearity of Chaparral Physic sensors ▫ 20 Pa p-p transition point to needing to evaluate whether the linearity will effect your results ▫ Wind Noise Filters ▫ Showed the frequency response of soaker hose and how it changes with length ▫ The small filters tested had no noise reduction advantage over an open microphone ▫ New Models from Chaparral Physics CP Research • ITW 2008 27

Questions?