Документ взят из кэша поисковой машины. Адрес оригинального документа : http://zebu.uoregon.edu/~uochep/talks/talks03/acousmit.pdf Дата изменения: Thu Oct 30 23:00:54 2003 Дата индексирования: Tue Oct 2 10:51:13 2012 Кодировка: Поисковые слова: п п п п п п п п п п п п п п п п п п п п п п п п п

ACOUSTIC MITIGATION PROGRESS

Robert Schofield, University of Oregon Doug Cook, Akiteru Takamori, LHO Jonathan Kern, Joe Kovalik, LLO AND MANY OTHERS

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PROBLEM
Red shows coherence between H1 and H2 AS_Q over 12h during S2
Coherence
0.3 H2:LSC-AS_Q / H1:LSC-AS_Q H0:PEM-BSC7_MIC / H2:LSC-AS_Q

0.25

0.2

Coherence

0.15

0.1

0.05

0

0

100

200

300

400

500

600

700

800

900

Frequency (Hz)
T0=09/03/2003 02:15:00 Avg=400 BW=0.0117178

Blue shows coherence between microphone near 4k dark port and 2k AS_Q 2

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Noise played through speaker during S2 indicated that all three interferometers were close to being limited over a broad frequency range by acoustic coupling
Power spectrum
10 10 10
3 H0:PEM-BSC7_MIC(REF0) H0:PEM-HAM1_MIC(REF1) H1:LSC-AS_Q(REF2) H0:PEM-BSC7_MIC(REF3) H0:PEM-HAM1_MIC(REF4) H1:LSC-AS_Q(REF5)

2

Magnitude

1 10 10 10 10
-1

-2

-3

-4

10 *T0=12/03/2003 05:29:46 *Avg=1

2

10

3

Frequency (Hz)
BW=0.187499

Black: AS_Q with noise; Red: normal; Orange: mic with noise; Yellow: normal We would like to reduce acoustic-seismic contribution to noise by 100 to 1000 3

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HOW COUPLING SITES WERE IDENTIFIED
Burst propagation delays:
4 3 2 1 0 -1 -2 -3 -4 126.3 20000 15000 10000 5000 0 -5000 -10000 -15000 -20000 126.3 6000
H0:PEM-HAM8_MIC butter('HighPass',4,100.0)

H2:LSC-AS_Q butter('HighPass',4,100.0)

126.35

126.4

126.45
H0:PEM-HAM10_MIC butter('HighPass',4,100.0)

126.5

126.35

126.4

126.45

126.5

4000 2000 0 -2000 -4000 -6000 126.3 4000 3000 2000 1000 0 -1000 -2000 -3000 -4000 126.35 126.4 126.45
H0:PEM-PSL2_MIC butter('HighPass',4,100.0)

126.5

Predominant Coupling Sites : All 3 dark ports, LHO 4k PSL

4

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HOW MUCH LOWER IS COUPLING AT OTHER TABLES?
21 Hz sawtooth played near LLO ISCT4 (top), ISCT1 (bottom)
Power spectrum
10 10 10
3

2

L0:PEM-HAM4_MIC L1:LSC-AS_Q

Magnitude

1 10 10 10 10
-1

-2

-3

-4

0

100

200

300

400

500

600

700

800

900

Frequency (Hz)
T0=11/02/2003 06:23:11 10 10 10
3

Avg=25

BW=0.187499 L0:PEM-HAM1_MIC L0:PEM-PSL1_MIC L1:LSC-AS_Q

2

Magnitude

1 10 10 10 10
-1

-2

-3

-4

0

100

200

300

400

500

600

700

800

900

Frequency (Hz)
T0=11/02/2003 06:35:54 Avg=25 BW=0.187499

For S2 coupling at other tables is at least a factor of 10 lower than at dark ports.

5:

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MAIN COUPLING MECHANISM: clipping modulated by acoustic excitation.
Evidence: acoustically excitable peaks in GW channel gradually increase as an iris on the dark port table is closed (see periscope peak just above 200 Hz). Calibration lines at harmonics of 50 Hz do not increase.
10
-1

H1:LSC-AS_Q(REF1) H1:LSC-AS_Q(REF0)

10

-2

Magnitude

10

-3

10

-4

10

2

10

3

Frequency (Hz)
*T0=18/04/2003 01:11:58 Avg=1 BW=0.75

Blue: Normal; Red: Iris increased clipping

6

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No evidence for parasitic interferometry noise from backscattering.
Red: Accelerometer on Dark Port Table; Blue: AS_Q Solid: Normal; Dashed: Shaker shaking table at 14 Hz (sway resonance)
p
10 10 10
4

3

H0:PEM-HAM4_ACCX(REF4) H1:LSC-AS_Q(REF7) H0:PEM-HAM4_ACCX(REF28) H1:LSC-AS_Q(REF31)

2

Magnitude

10 1 10 10 10 10
-1

-2

-3

-4

10

2

Frequency (Hz)
*T0=21/05/2003 08:11:03 Avg=1 BW=0.187499

7

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ACOUSTIC SOURCES
S2 LVEA sound levels are similar to those of an average residence
Location near LHO 2k dark port, outside of ISCT10 near LHO 4k dark port, outside of ISCT4 near LHO 2k reflected port, outside of ISCT7 1m from ajar electronics rack 1m from closed electronics rack 1m from vacuum pipe feed-through into mechanical room mechanical room bay between mechanical room and LVEA 50 53 56 59 57 56 65-70 52 dBC

Continuous sources: mostly HVAC and electronics fans Transients: building relaxation, airplanes etc.; these are hard to control and comparable in loudness to our fans etc. For Burst Group analysis there isn't much to gain by reducing our lab sound level. However, continuous acoustic sources are important for the Stochastic Group. 8

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LOUDEST CONTINUOUS SOURCES: HVAC below 100 Hz, electronics cabinets above.
Rattling ducts may contribute to HVAC noise Black: HVAC off, LVEA mic; Blue: HVAC on; Red: hand rattling of single walled duct.
Power spectrum
10
2

H0:PEM-BSC7_MIC(REF30) H0:PEM-BSC7_MIC(REF32) H0:PEM-BSC7_MIC(REF21)

Magnitude

10

1

0

20

40

60

80

100

120

140

160

180

Frequency (Hz)
*T0=14/05/2003 23:22:21 *Avg=1/Bin=2 BW=0.187499

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PROPAGATION FROM SOURCE TO COUPLING SITE

Speaker on floor outside LLO triple PSL enclosure: comparison of inside to outside sensors
Frequency Hz 100 200 500 800 29 114 111 100 Microphone: Outside/ Inside Accelerometer: Outside/ Inside 17 89 67 100

Enclosures appear to reduce table acceleration as well as sound pressure level.

Signal seems to travel predominantly through the air. 10

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MITIGATION PLANS
I. REDUCE COUPLING (factor of 10 to 20) A. Clipping 1) Eliminate some clipping sites (e.g. EO shutter) 2) Larger optics where needed; lighter mounts for higher resonant frequencies 3) Damp mounts and dumps etc. 4) New periscopes with higher frequency resonances and damping 5) Reduce table resonances around 100 Hz B. Backscattering from table (out of prudence - we haven't seen coupling) 1)Rigid legs or float table II. ACOUSTICALLY ISOLATE WORST COUPLING SITES (factor of 10 to 20) A. Dark port enclosures with internal absorption kits III. REDUCE CONTINUOUS SOURCES (factor of 3 to 5) A. Remove most electronics cabinets from LVEA B. Absorption and damping kits for vacuum electronics cabinets C. Damp single walled sections of ducts D. Insulate pipe feed through from mechanical room E. Insulate PSL chillers

11

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CLIPPING MITIGATION SINCE S2
1) Replaced the top optic mount on the dark port periscope with a lighter one 2) Eliminated some small apertures since S2: EO shutter and associated polarizers Old Mount New Mount New Path EO shutter sidelined

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REDUCTION IN ACOUSTIC COUPLING SINCE S2
Red: AS_Q normal; Black: AS_Q with noise; Yellow & Orange: BSC7 mic March 12
H0:PEM-BSC7_MIC(REF0)

10 10

-12

H0:PEM-HAM1_MIC(REF1) H1:LSC-AS_Q(REF2) H0:PEM-BSC7_MIC(REF3) H0:PEM-HAM1_MIC(REF4) H1:LSC-AS_Q(REF5)

-13

m/sqrt(Hz)

10 10 10 10 10 10

-14

-15

-16

-17

-18

-19

10

2

10

3

Frequency (Hz)

August 9
10 10
-11 -12 -13

Magnitude (m/Hz

1/2

10 10 10 10 10 10 10

H1:LSC-AS_Q(REF35) H1:LSC-AS_Q(REF39) H0:PEM-BSC7_MIC(REF38) H0:PEM-BSC7_MIC(REF42) H0:PEM-HAM1_MIC(REF36) H0:PEM-HAM1_MIC(REF40)

)

-14

-15

-16

-17

-18

-19

10

2

10

3

Frequency (Hz)
*T0=09/08/2003 04:10:03 Avg=1 BW=0.187499

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TESTING OF NEW PERISCOPE DESIGN WITH DAMPING
Accelerometer on periscope top; Blue: no damping Red: damping
Power spectrum
H1:GDS-TEST_34_1_20(REF5)

Damping

10

2
H1:GDS-TEST_34_1_20(REF8)

Magnitude

10

1

100

200

300

400

500

600

700

800

900

Frequency (Hz) *T0=01/08/2003 02:31:49 Avg=1/Bin=8 BW=0.187499

14

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TESTS OF RIGID AND FLOATING TABLE LEGS

10

-7

Rigid Legs
10
-8

Floating Legs

normal leg 34" tripod leg minus-k leg air leg

Displacement [m/Hz ]

1/2

10

-9

10

-10

10

-11

10

-12

10

-13 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9

10

100

Frequency [Hz]

Sum in quadrature of 3 accelerometer axes

15

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DARK PORT ENCLOSURES WITH ABSORPTION KITS

Enclosure: attenuation factor of about 10 at low f; with absorption kit, 20 to 30
2

Attenuation Ratio (median)

0.1
9 8 7 6 5

4

3

w/o absorber w/ absorber
500 1000 1500 2000 2500

average: 0.19 average: 0.07
3000

Frequency [Hz]

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MITIGATION OF CONTINUOUS SOURCES:
Remove 4k electronics cabinets from LVEA, place 2k cabinets in acoustic enclosures, internal absorption for vacuum cabinets and PSL chiller enclosures. Damp sections of single walled ducts.

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