Alexandra Loubeau

High-frequency measurements of blast wave propagation

Blast wave propagation measurements were conducted to investigate nonlinear propagation effects on blast waveform evolution with distance. Measurements were made with a wide-bandwidth capacitor microphone for comparison with conventional 3.175-mm (1/8-in.) microphones with and without baffles. It was found that the 3.175-mm microphone did not have sufficient high-frequency response to capture the actual rise times in some regions. For a source of 0.57 kg (1.25 lb) of C-4 plastic explosive, the trend observed is that nonlinear effects steepened the waveform, thereby decreasing the shock rise time, up to a range of 50 m. At 100 m, the rise times had increased slightly.

A new evaluation of noise metrics for sonic booms using existing data

An evaluation of noise metrics for predicting human perception of sonic booms was performed. Twenty-five metrics were chosen from standards and from the literature in an effort to include all potentially relevant metrics. Three different datasets of sonic boom waveforms and associated human response were chosen to span a variety of signals, including traditional N-waves with various shock shapes and rise times, and predicted waveforms from designs of low-boom aircraft for a variety of aircraft sizes. These datasets were derived from laboratory studies conducted in sonic boom simulators at NASA Langley Research Center and JAXA. Simulations of booms experienced in both outdoor and indoor environments were included by using different facilities at NASA or modifications to facility configurations at JAXA. American and Japanese test subjects participated at NASA and JAXA, respectively. Ratings of loudness using a magnitude estimation technique and ratings of annoyance using a category line scaling method are i...

Overview of an indoor sonic boom simulator at NASA Langley Research Center.

A facility has been constructed at NASA Langley Research Center to simulate the soundscape inside residential houses that are ensonified by environmental noise from aircraft. The purpose of this facility, the interior effect room, is to examine parameters that affect psychoacoustic response in a controllable indoor listening environment. The single room facility, built using typical residential construction methods and materials, is surrounded on two sides by arrays of loudspeakers. These exterior arrays are used to simulate aircraft noise sources that transmit into a room of a typical house. The exterior sound reproduction system, which consists of 52 subwoofers and 52 mid‐ranges in close proximity to the walls of the room, has been designed to enable study of sonic booms transmitted into residential structures and has a usable bandwidth of 3 Hz–6 kHz. In addition to these exterior arrays, satellite speakers placed inside the room are used to simulate rattle and other audible contact‐induced noise that can result from low frequency excitation of a residential house. The layout of the facility, operational characteristics, acoustical characteristics, and equalization approaches are summarized. Current research efforts utilizing the facility are described in two companion papers.

Effects of indoor rattle sounds on annoyance caused by sonic booms

To expand national air transportation capabilities, NASAs Commercial Supersonic Technology Project is working to make supersonic flight practical for commercial passengers. As an aid in designing and certifying quiet supersonic aircraft, a noise metric is sought that will correspond to indoor annoyance caused by sonic booms, including the effects of indoor rattle sounds. This study examines how well several common aircraft noise metrics predict indoor annoyance based on the indoor and outdoor sound fields. The results suggest notional community annoyance models that include the effects of indoor rattle sounds.

Evaluation of the effect of aircraft size on indoor annoyance caused by sonic booms

Sonic booms from recently proposed supersonic aircraft designs developed with advanced tools are predicted to be quieter than those from previous designs. The possibility of developing a low-boom flight demonstration vehicle for conducting community response studies has attracted international interest. These studies would provide data to guide development of a preliminary noise certification standard for commercial supersonic aircraft. An affordable approach to conducting these studies suggests the use of a sub-scale experimental aircraft. Due to the smaller size and weight of the sub-scale vehicle, the resulting sonic boom is expected to contain spectral characteristics that differ from that of a full-scale vehicle. To determine the relevance of using a sub-scale aircraft for community annoyance studies, a laboratory study was conducted to verify that these spectral differences do not significantly affect human response. Indoor annoyance was evaluated for a variety of sonic booms predicted for several d...

Laboratory study of outdoor and indoor annoyance caused by sonic booms from sub-scale aircraft

Advances in integrated system design tools and technologies have enabled the development of supersonic aircraft concepts that are predicted to produce sonic booms with lower loudness levels while maintaining aerodynamic performance. Interest in the development of a low-boom flight demonstration vehicle for validating design and prediction tools and for conducting community response studies has led to the concept of a sub-scale test aircraft. Due to the smaller size and weight of the sub-scale vehicle, the resulting sonic boom is expected to contain spectral characteristics that differ from that of a full-scale vehicle. In order to justify the use of sub-scale aircraft for community annoyance studies, it is necessary to verify that these spectral differences do not significantly affect human response. The goal of the current study is to evaluate both outdoor and indoor annoyance caused by sonic booms predicted for these two classes of vehicles. The laboratory study is conducted in two sonic boom simulators...

Evaluation of an indoor sonic boom subjective test facility at NASA Langley Research Center

A sonic boom simulator at NASA Langley Research Center has been constructed for research on human response to low-amplitude shaped sonic booms heard indoors. Research in this facility will ultimately lead to development of a psychoacoustic model for single indoor booms. The first subjective test was designed to explore indoor human response to variations in sonic boom rise time and amplitude. Another goal was to identify loudness level variability across listener locations within the facility. Finally, the test also served to evaluate the facility as a laboratory research tool for studying indoor human response to sonic booms. Subjects listened to test sounds and were asked to rate their annoyance relative to a reference boom. Measurements of test signals were conducted for objective analysis and correlation with subjective responses. Results confirm the functionality of the facility and effectiveness of the test methods and indicate that loudness level does not fully describe indoor annoyance to the selected sonic boom signals.

Updated evaluation of sonic boom noise metrics

There is no internationally agreed-upon standard noise metric that can be used to quantify sonic boom levels from overflight of supersonic aircraft. Several laboratory studies have investigated perception of sonic booms in outdoor environments, as well as in indoor environments, where transmission loss alters the spectral content and level of the sonic boom and additional factors such as secondary rattle noise and vibration affect perception. Each study has previously been evaluated separately for performance of noise metrics, and the results do not clearly indicate a preferred metric. Meta-analyses have also been performed to evaluate the performance of metrics across five of these studies. An additional sixth study of human response that incorporates rattle noise resulting from sonic booms at representative levels was recently conducted and has been added to the meta-analysis. The analysis considered thirteen metrics with three meta-analysis methodologies: individual subject ratings for indoor studies, mean ratings for indoor studies, and mean ratings for both indoor and outdoor studies. Considering both indoor and outdoor studies, this latest analysis confirmed previous results on the five metrics with highest correlation (r2) across studies: PL, BSEL, DSEL, ESEL, and ISBAP (Indoor Sonic Boom Annoyance Predictor). There is no internationally agreed-upon standard noise metric that can be used to quantify sonic boom levels from overflight of supersonic aircraft. Several laboratory studies have investigated perception of sonic booms in outdoor environments, as well as in indoor environments, where transmission loss alters the spectral content and level of the sonic boom and additional factors such as secondary rattle noise and vibration affect perception. Each study has previously been evaluated separately for performance of noise metrics, and the results do not clearly indicate a preferred metric. Meta-analyses have also been performed to evaluate the performance of metrics across five of these studies. An additional sixth study of human response that incorporates rattle noise resulting from sonic booms at representative levels was recently conducted and has been added to the meta-analysis. The analysis considered thirteen metrics with three meta-analysis methodologies: individual subject ratings for indoor studies,...

Effects of chair vibration on indoor annoyance ratings of sonic boomsa)

The effects of perceptible whole-body vibrations on annoyance ratings of sonic booms and other impulsive environmental sounds experienced indoors were studied. Fifteen pairs of test subjects made annoyance ratings while seated in a living room environment. There were two chairs, one isolated from floor vibrations and the other not isolated, and every test subject rated all signals in both chairs. Halfway through each test session, subjects changed seats. Subjects who sat in the isolated chair first gave lower mean annoyance ratings in both halves of the test than subjects who sat in the non-isolated chair first. Annoyance predictions from models using both sound and vibration measures were closer to average annoyance ratings than predictions from a model using sound measures alone. Reformulation of the annoyance model revealed that the presence of perceptible vibration is equivalent to increasing acoustic metric Perceived Level by 4.8 dB when calculated on exterior signals and by 5.6 dB when calculated on interior signals.

Evaluation of the effect of aircraft size on indoor annoyance caused by sonic booms and rattle noise

NASA plans to use a low-boom flight demonstration supersonic aircraft for community annoyance studies of sonic booms. As previously reported, laboratory studies were conducted in NASAs Interior Effects Room (IER) to help determine the relevance of using a sub-scale aircraft. Indoor annoyance was evaluated for a variety of sonic booms predicted for several different sizes of vehicles, whose levels were adjusted to the same range of loudness levels. Although no significant effect of aircraft size was found for equivalent loudness levels, a new laboratory study was conducted in the IER to extend this investigation to include the effect of secondary rattle noises. The rattle noise playback was determined from window rattle measurements performed in the IER that resulted in a database of rattle noises matched with sonic booms predicted for different aircraft, at different boom levels. The main objective was to test whether aircraft size is still not significant when realistic window rattles are included in th...