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Binaural signals have been used to approximate the auditory of the dive, whereas the second boom is from the earlier part
experience of sonic boom and rattle exposure in different- of the dive because the supersonic speed of the aircraft has
sized rooms through the use of models and filtering allowed it to outrun the propagating wavesl
(Giacomoni and Davies, 2013; Loubeau et al., 2013c). Some
limitations of this playback equipment are the absence Human Response Studies
of experiencing the sounds in a real space with natural Human Response to 0iitdaarBaams
reverberation, the absence of tactile vibration, and decreased Many human response tests were performed in NASA’s
realism due to limited low-frequency reproduction. High- outdoor sonic boom simulator in the 19905 (Leatherwood
quality systems of amplifiers and headphones have mitigated et al., 2002). These laboratory studies were designed to
this last point somewhat, but the systems are still more investigate a wide range of shaped sonic boom signatures
restricted than subwoofer systems for reproducing the full and to gather human perception of loudness and annoyance.
frequency content of the sonic booms. Shaped booms were rated less loud than symmetric N-waves,
Finally, newer simulators allow for more realistic indoor and sevéml nolse_me_mCs were evalualed for their ablilty
soundscapes for investigating causes of elewted annoyance to Predicl ‘he ‘“"J“_“"° resI_)m_‘se' As_ a resuh of PL b_emg
to sonic booms experienced indoors. One configuration Chose‘) as the best noise memcf it has since been_ “Sid widely
(Naka, 2013) consists ofa small booth ma‘ can be Configured to design and assess characteristics of supersonic aircraft.
for indoor listening using a partition with awindow. Another Evaluation of the realism of outdoor boom simulation was
installation called the Interior Effects Room (IER; Klos et al., conducted with simulators and real booms from overflights
2008) at the NASA Langley Research Center consists of a of asupersonic aircraft (Sullivan et al., 2008). PL values were
small room configured as a living room with loudspeaker found to be highly correlated between field recordings and
playback over arrays adjacent to two exterior walls of the simulator reproduction, and the results increased confidence
simulator. The realistic indoor soundscape and environment, in the use of simulators for human response testing. It was
augmented with the ability to control secondary rattle noises noted that very low frequency energy (less than 7 Hz) was
and vibration, have enabled systematic studies of the factors not significant for assessing realism to booms experienced
contributing to human annoyance to sonic booms. in an outdoor environment.
Sonic boom subjective studies have also been conducted with Outdoor Versus Indoor Response
rea.l supersonic overflights of aircraft. In the past, these studies Afield studyconductedbyNASA compared perception ratings
were limited to assessing the response to very loud booms, from test subjects seated inside and outside a house overflown
usually produced with military aircraft. However, a special by a supersonic airplane using the low-boom dive maneuver
flight maneuver called a low-boom dive has been developed (Sullivan et al., 2010). Although the annoyance ratings
(Haering et al., 2005) to mimic the lower amplitudes at the showed that indoor and outdoor annoyance were the same for
ground that would be expected from supersonic overflight the same noise exposure, a posttest questionnaire highlighted
of future aircraft. By adjusting the location of the dive, and a.n increase in annoyance indoors. This inconsistency could
hence the propagation distance, the ground sonic boom can possibly be attributed to the methodology chosen or to the
be varied in level over a geographic area. presence of a rattle indoors.
This maneuver has been used successfully in several field A series of subjective tests with playback of measured low-
studies to create a variety of boom loudness levels that would amplitude sonic booms was conducted (Miller, 201 1) to
otherwise not be possible with today’s aircraft in steady, level further explore the inconsistency discovered by Sullivan
flight. This dive maneuver is not withoutlimitations for dose- et al. (2010). Three different listening environments were
response testing though because it creates a double boom explored, including headphones indoors, headphones
of low-amplitude N-waves. In this maneuver, the aircraft outdoors, and an outdoor simulator (Salarnone, 2005), and
executes an inverted dive from 50,000 feet and transitions the sa.me set of signatures was used in each case. Active
to level flight above 30,000 feet (see Sparrow, 2006 for a listeners found indoor signatures more annoying than
diagram of the maneuver). The aircraft creates shock waves outdoor signatures regardless of listening environment,
continuously while it is moving faster than Mach 1. The first and signatures experienced indoors were considered more
boom to arrive at the area of interest is from the latter part annoying.

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