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modulators. This system can generate sound pressure levels up to 160 dBSPL. Each acoustic chamber has its own configurations, but each siren is centered on a frequency where sound pressure levels are the highest. In some cases these sirens can be completed with electroacoustic systems to generate and
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103:
field where there is no privileged direction of the energy. In other words, when sound pressure is the same everywhere in the room. This is obtained with large rooms with no absorbent materials on walls, ceiling or floor. Diffusion is enhanced in asymmetric rooms. To obtain such conditions, the room
354:
Frequency is a main factor of a good diffused field. Some phenomena linked to frequency of the sound pressure field lead to poor homogeneity of a pressure field. The frequency response of a room is the amplification or reduction of some frequencies. It represents the repartition of pressure with
851:
Acoustic tests are mainly use for environmental tests on aircraft structures. Satellites are expensive products with high-engineering built-in components. To improve the resistance of a spacecraft during launch and during its orbital life, analysis is focused on tests in three categories :
333:
Many theoretical ways to model sound propagation are used. One of these is the geometrical approach. This represents sound waves as a ray of energy propagating. When it meets an obstacle, this ray has two possible behaviors: It can be reflected following the normal of the plan,
355:
respect to frequency. In low frequencies this can lead to mode apparition. These modes are due to standing waves that lead to maximum and minimum pressure according to the geometry of the room. To determine the frequency for which the pressure field can be considered diffused,
982:
To test a satellite, a sound generation system generates a broadband spectrum (Hz) simulating the maximum envelope of all launchers that the satellite may fly in. To qualify, three tests are realized with changing global gain compared to launcher spectrum:
186:. It can be obtained by measuring the sound pressure decrease after a sound impulse or by using approximate formulas such as Sabine's or Eyring's. In the case of a diffuse field (low absorption on the walls, and big volumes) Sabine's formula is used.
954:
Acoustics creates mechanical stresses during the first five seconds. Sound pressure levels can go up to 150 dBSPL. Acoustic tests are used to verify the mechanical resistance of the satellite and its elements to acoustic pressures generated.
118:
Reverberation is due to multiple reflections on walls with some delays that come back to the receptor. Summing up these contributions, a reverberant pressure field is created. The more reverberation, the more the field is diffused.
512:
91:, acoustic chambers are the main facilities for such tests. A chamber is a reverberant room that creates a diffuse sound field and is composed of an empty volume (from 1 m to 2900 m) and a multifrequency sound generation system.
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High frequency control : If no high frequency sirens or electroacoustic devices are included, only harmonics generated by distortion produce mid and high frequencies.
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661:{\displaystyle f_{lmn}={\frac {c_{0}}{2}}{\sqrt {\left({\frac {l}{L_{x}}}\right)^{2}+\left({\frac {m}{L_{y}}}\right)^{2}+\left({\frac {n}{L_{z}}}\right)^{2}}}}
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must be reverberant. The source's direct field must be negligible compared to the reverberant field, avoiding privileged propagation.
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To produce exact levels, piloting microphones check sound pressure levels and apply a realtime gain correction to adjust the level.
864:. This last test area is focused on the mechanical stresses that the specimen will meet during its life, especially during launch.
969:
Once the sound generation system is working, acceleration measurement is performed by accelerometers placed on the specimen.
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For example, in the case of a rectangular room, low frequency modes are determined relative to the room dimensions as
17:
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Acoustique générale: équations différentielles et intégrales, solutions en milieux fluides et solides, applications
853:
329:
Schematic representation of specular (in blue) and diffused (in green) reflections of an incident wave ray (in red)
191:
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appears that leads to higher harmonics. Loudspeakers are used in some chambers to control these frequencies.
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control midrange and high frequencies. Sirens generate low frequencies, but with high sound pressure levels
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is the testing of the mechanical resistance of a spacecraft to the acoustic pressures during launch.
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Before testing the satellite, an empty room test is performed to check the chamber's signature.
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is commonly used. It is obtained considering the frequency from which the modal overlap exceeds
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Security : Control with piloting microphones that adjust the level or abort if needed
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Low frequency generation : Very efficient low frequency generation (below 50 Hz)
857:
385:. Below this frequency, the field is not diffuse and standing waves create pressure modes
362:
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182:. These values are the interval for the sound pressure level to the lower of 30 or 60
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Two oft-used measures of reverberation time quantify this parameter, :
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Schematic transverse cut view of pressure modes in a duct (closed-closed)
499:
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This pressure field is generated by multifrequency sirens powered by
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183:
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Representativeness : Faithful to real stresses during launch
1025:
Homogeneity : Spatial homogeneity guaranteed for ± 1.5 dBSPL
26:
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Gas generation : May require large amounts of nitrogen
1037:
Well known process : Used by many aerospace industries
271:
is the equivalent absorption area involving the surface
57:
47:
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NASA's Space Power
Facility (SPF) Knowledge (XXG) page
437:{\displaystyle F_{s}=2000{\sqrt {\frac {RT_{60}}{V}}}}
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Draft:Diffuse field acoustic testing (space facility)
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1110:Tustin, Wayne; Mercado, Robert (1 August 1984).
291:of the walls and their absorption coefficient
993:PFM (Proto Flight Model) : 0 dB SPL
99:Theoretically, diffuse field is defined as a
8:
350:Quantities involving diffuse pressure field
1083:Potel, Catherine; Bruneau, Michel (2006).
1060:Thales Alenia Space (Cannes) : 1000 m
884:Acoustic vibration and quasi-static loads
881:First Stage ignition and boosters ignition
476:is the reverberation time of the room and
227:{\displaystyle RT_{60}=0.16{\frac {V}{A}}}
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1137:Maral, Gerard; Bousquet, Michel (2009).
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731:are respectively the mode of the length
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264:{\displaystyle A=\sum S\times \alpha }
7:
1167:Thales Alenia Space Official Website
990:Intermediate : - 4 dB SPL
1182:Intespace's acoustic test facility
1116:. Tustin Institute of Technology.
965:Vibration § Vibration testing
25:
876:Resulting mechanical aggressions
987:Low-Level : - 8 dB SPL
31:
1113:Random vibration in perspective
843:of sound in the working fluid.
1063:IABG (Ottobrunn) : 1378 m
82:Diffuse field acoustic testing
1:
1172:IABG Space Official Website
1218:
962:
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959:Accelerometer measurement
948:Clamp band release shock
921:Second stage extinction
469:{\displaystyle RT_{60}}
304:{\displaystyle \alpha }
175:{\displaystyle RT_{60}}
145:{\displaystyle RT_{30}}
95:Diffuse field principle
46:, as no other articles
940:Sinusoidal vibrations
937:Third stage extinction
924:Sinusoidal vibrations
900:Sinusoidal vibrations
897:First stage Extinction
892:Sinusoidal vibrations
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1143:(5 ed.). Wiley.
905:Second Stage ignition
847:Aerospace application
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832:{\displaystyle c_{0}}
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932:Quasi-static loads
908:Quasi-static loads
889:Boosters extinction
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378:{\displaystyle M=3}
344:diffused reflection
336:specular reflection
1066:NASA : 2860 m
945:Spacecraft release
916:Pyrotechnic shock
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108:Reverberation time
89:aerospace industry
65:for suggestions.
55:to this page from
1150:978-0-470-71458-4
1123:978-0-918247-00-1
1096:978-2-7298-2805-9
952:
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858:Radio-frequencies
724:{\displaystyle n}
704:{\displaystyle m}
684:{\displaystyle l}
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489:{\displaystyle V}
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284:{\displaystyle S}
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978:Sound generation
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873:Launch steps
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1191:Categories
1071:References
1020:Advantages
1011:distortion
963:See also:
862:Vibrations
319:See also:
112:See also:
61:; try the
48:link to it
1202:Acoustics
299:α
259:α
256:×
250:∑
70:June 2016
51:. Please
1055:Examples
1002:nitrogen
841:celerity
854:Thermal
87:In the
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671:Where
446:Where
236:Where
44:orphan
42:is an
184:dBSPL
1145:ISBN
1118:ISBN
1091:ISBN
860:and
839:the
785:and
711:and
408:2000
212:0.16
152:and
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72:)
68:(
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