Jonathan Rathsam

Annoyance to Noise Produced by a Distributed Electric Propulsion High-Lift System

Results of a psychoacoustic test performed to understand the relative annoyance to noise produced by several configurations of a distributed electric propulsion high lift system are given. It is found that the number of propellers in the system is a major factor in annoyance perception. This is an intuitive result as annoyance increases, in general, with frequency, and, the blade passage frequency of the propellers increases with the number of propellers. Additionally, the data indicate that having some variation in the blade passage frequency from propeller-to-propeller is beneficial as it reduces the high tonality generated when all the propellers are spinning in synchrony at the same speed. The propellers can be set to spin at different speeds, but it was found that allowing the motor controllers to drift within 1% of nominal settings produced the best results (lowest overall annoyance). The methodology employed has been demonstrated to be effective in providing timely feedback to designers in the early stages of design development.

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.

Sound‐pressure level distribution in a long, narrow hallway: Measurements versus results from a computer model with scattering from surface roughness and diffraction

The sound‐pressure level distribution down a long, narrow hallway due to a sound source at one end does not decrease linearly along the length of the hall. This characteristic may be due to the changing behavior of scattering that occurs down the length of the hallway, which is distance‐ and angle‐dependent. A new scattering method that incorporates these effects has been implemented in the room acoustic computer modeling program, odeon [C. L. Christensen and J. H. Rindel, Forum Acusticum, Budapest (2005)]. A comparison of the results from an odeon model with real‐world measurements along a long, narrow hallway on the campus of the Technical University of Denmark is provided in this paper. [Work supported by the NSF.]

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.

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.

Sensitivity of room acoustic parameters to changes in scattering coefficients

This project uses the room acoustics computer modeling program, ODEON, to investigate the sensitivity of room acoustic parameters to changes in scattering coefficients. Particularly, the study is interested in determining if the results from certain room models are more sensitive to scattering coefficients than from other models, due to their geometry or absorption characteristics. If so, how can one quantify a model’s susceptibility to being sensitive to scattering? Various models of three real spaces in Omaha, Nebraska are tested. The predicted reverberation, clarity, and spaciousness parameters are compared at various receiver locations, while the scattering coefficient of all surfaces is varied from 0 to 0.1, 0.3, 0.5, and 0.8. The resulting data are analyzed by frequency according to the (1) average absorption of the room; (2) magnitude variation of absorption within the room; (3) spatial distribution of absorption within the room; and (4) level of model detail. Initial results indicate that paramete...

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.

Dose-response model comparison of recent sonic boom community annoyance data

To enable quiet supersonic passenger flight overland, NASA is providing national and international noise regulators with a low-noise sonic boom database. The database will consist of dose-response curves, which quantify the relationship between low-noise sonic boom exposure and community annoyance. The recently-updated international standard for environmental noise assessment, ISO 1996-1:2016, references two fitting methods for dose-response analysis. Fidell’s community tolerance method is based on theoretical assumptions that fix the slope of the curve, allowing only the intercept to vary. By contrast, Miedema and Oudshoorn’s method is based on multilevel grouped regression. These fitting methods are applied to an existing pilot sonic boom community annoyance data set from 2011 with a small sample size. The purpose of this exercise is to develop data collection and analysis recommendations for future sonic boom community annoyance surveys.

Summary of “Statistical learning and data science techniques in acoustics research”

Increases in computational capabilities have made statistical learning and data science techniques more accessible to researchers. This paper summarizes research presented in two special sessions, one each at the Spring 2016 meeting in Salt Lake City, UT and the Spring 2017 meeting in Boston, MA. The sessions were cosponsored by the Noise and Signal Processing Technical Committees. The speakers represent industry, academia, and government institutions in the United States, France, England, and the Netherlands. Presentation topics covered a variety of acoustic disciplines with a focus on machine learning techniques, Bayesian techniques, and advanced statistical models.