Page 26 - Fall_DTF

Perception of sense Beams
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than the sounds from conventional aircraft. Although ‘“" im W
subsonic aircraft noise is a concern near airports, the sonic i W 3; “’
booms from supersonic aircraft are created along the entire " ' E N’ r ‘"‘
supersonic route and could potentially affect large segments A l" U, '"m:“:‘:l'W ' ‘l
onhe population. . .. K .. =
_ _ _ _ _ rmm D""m“‘n"mF‘¢‘lu-:ii.\ tn» o.,t.r.ns.rtr.t.n...,.n.i
Wm‘ “‘l"“'_‘°°‘ "‘ _“"““&'sh“P‘_"3 ‘°°h“"l“”’ ‘“°d"“ Figure 1. Cumparisan nfsanic lwam wavefarms and speetrafar the
5“P°“°“" “"‘”f‘ d“5‘5“5 “'9 P'°d“‘°d ‘° “me 5h“P“‘l '°“" Canearde arid an airliner eaneept designed far law—ampIitude shaped
amplimde sonic boom heard on the ground that axe much beams 0. persanal eammunieatian). Examples 0; imam
quieter than conventional N-wave sonic booms from the shapes. b: Variatian in frequency spectra. 5: Variatian in laudness
Concorde (see Figure 1). The significant reduction inwaveform 5P9C"‘1-
a.rnplitude and increase i.ri shock rise time lead to a reduction in
sound pressure level spectra, particularly at higher frequencies cm. ___ N‘ /
where the reduction ca.ri reach 60 dB. Accordingly, the loudness "'”""" /\r./ ' W
. s a in-
spectra are also reduced by over a factor of 10 in sones over / and W
most of the frequency range critical to human hearing. This \\
reduction in the high-frequency content results i.ri a sound like JV '
a “thump” rather than a sharp crack or boom. iC:':l'c'v-in \ ( efi/V‘
llllilhlll _
Historically, the maximum overpressure was used to describe \§ // “‘"'!t:I:fl:!.".
the level of sonic booms. Years of research using outdoor sonic /. /"
boom simulators, however, resulted in identification of PL /' Z’ \
iru * A/xfix‘
(Stevens, 1972; Shepherd and Sullivan, 1991) as a noise metric 3...," “I S-TM I-am
that works best foravariety of signature shapes (Leatherwood F‘ 2 S h ti _ b d (M I_ _ t I
et al., 2002). Annoyance to sonic boorris experienced i.ridoors 2?’? 5"’; Z’; ‘Z; 21:‘ ‘:’g;|”:“;eN7w';i::;:V:n':
Presents additional factors related to the building itself tiahai sanic beam: At the edge af the primary carpet is the lateral
71” smut‘: Baum Carpet cutafl edge with a unique signature that generally dues -not eantain
_ _ _ large shacks. Light gray, seearrdary beam carpet containing wave—
50"“ "°°‘“5 3” P”55“" d‘5‘“"’““3“ ‘“““‘l by’ ‘"1"’ 5°'“‘ farms with indistinct characteristics that saund Iihe rumbles at i1is—
flight that teach the st0|1nd- Figure 2 Shows the different tant thunder The transitianfram sulzsanic ta supersonic flight creates
regions of sonic booms including the primary boom carpet, a faeused sanic baam signature with an accentuated high—ampIi'tude
the transifion focus_ and the secondary boom carPg[_ initial shack. The black and white under the centerline Hf the flight
track arid across the carpet indicate the relative averpressme levels
. . . A h ii" ' h.
Sonic Boom Nuiee Generation ( P)/E” e mimmsegmems affllg t
for Subjective Studies
L“b°"“t°rY 5lm“l‘“°’5 have been “Sen elfe‘3nVelY lo 5l“‘lY boom result in contact-induced rattle noise from elements
nnman annoyance to 3 b"°ad “"39 0f 5°nl‘5 boom signals such as windows, doors, and objects inside rooms.
undercontrolledconditions(Maglieri etal.,2014).Sirnulators _ _ _ _ _
. Most outdoor sonic boom simulators consist of an airtight,
can reproduce measured booms as well as booms predicted all _ _d all d b th Th _ _ d _ _‘h b f
for aircraft designs. They can also be used to investigate Sm Hg‘ -W e 00 ' ecavltyls nvfl_1w‘ 5“ wo_0 ‘fr
. loudspeakers to reproduce the low frequencies characteristic
the human response to different waveform parameters and _ _ _
. . . . . . of sonic booms, whereas midrange loudspeakers fill in the
interactions. The majority of simulators reproduce sonic t f th F ‘ t An th _ 1 t d _
booms as they would be experienced outdoors, although "5 $1 6 Per “fen SPEC mm‘ 0 er sm_m a or 6533“
. . consists of a mobile trailer that creates a traveling wave using
filtered outdoor waveforms or recordings of indoor _
. . an array of loudspeakers, a folded horn, and an anechoic
waveforms have also been presented to estimate the indoor t _ ti S 2005
environment. Most simulators, however, lack indoor realism “mum on ( one’ )‘
because there is an absence of space and reverberation as High-quality headphones or earphones are also used to
well as of structural vibrations and rattle. These structural reproduce the audible content of sonic booms and secondary
vibrations that occur in a building when impacted by a sonic rattle noises typically encountered in indoor environments.
24 1 AI:i:iuII:lr:I -risuay 1 Fnlllom