Clothilde Giacomoni

The effects of different test methods on the just noticeable difference of clarity index for musica)

The just noticeable differences (JNDs) of room acoustics metrics are necessary for research and design of performing arts venues. The goal of this work was to evaluate the effects of different testing methods on the measured JND of clarity index for music (C80). An initial study was conducted to verify the findings of other published works that the C80 JND is approximately 1 dB, as currently listed in ISO 3382:2009 (International Organization for Standardization, Switzerland, 2009), however, the results suggested a higher value. In the second study, the effects of using two variations of the method of constant stimuli were examined, where one variation required the subjects to evaluate the pair of signals by listening to each of them in their entirety, while the second approach allowed the participants to switch back and forth in real-time. More consistent results were obtained with the latter variation and the results indicated a C80 JND greater than 1 dB. In the final study, an extensive training period using the first variation was required, based on the second study, and the data were collected using the second variation. The analysis revealed that for the conditions used in this study (concert hall and chamber music hall) that the C80 JND is approximately 3 dB.

Effect of room characteristics on perception of low-amplitude sonic booms heard indoors

Supersonic flight over inhabited territories of the United States has been banned by the Federal Aviation Association. While research has been conducted to determine the effects of sonic booms on the general population when heard outdoors, little work has been done on people’s perception of sonic booms as heard indoors. A sound’s waveform will change in its transmission from outdoors to indoors due to several factors, one of which is the indoor acoustic environment. This can be changed using different room sizes, shapes or which materials are covering each surface (wall, ceiling, or floor). A subjective test, designed to determine which of these room characteristics has an effect on people’s ratings of annoyance, has been completed. It was found that smaller rooms and square rooms are rated as more annoying than larger rooms or rooms with a corridor-like or rectangular shape, and that rooms with lower reverberation times were rated as less annoying than rooms with higher reverberation times.

Comparison of Spatial Correlation Parameters between Full and Model Scale Launch Vehicles

The current vibro-acoustic analysis tools require specific spatial correlation parameters as input to define the liftoff acoustic environment experienced by the launch vehicle. Until recently, these parameters have not been very well defined. A comprehensive set of spatial correlation data were obtained during a scale model acoustic test conducted in 2014. From these spatial correlation data, several parameters were calculated: the decay coefficient, the diffuse to propagating ratio, and the angle of incidence. Spatial correlation data were also collected on the EFT-1 flight of the Delta IV vehicle which launched on December 5, 2014. A comparison of the spatial correlation parameters from full scale and model scale data will be presented.

Impact of Drift on the Vehicle Liftoff Acoustic Environments

During liftoff, a vehicle can drift due to wind, nozzle gimbaling, fly away maneuver, etc. This drift can cause the exhaust plumes to impinge on the deck and cause the noise levels experienced by the vehicle to increase. A small increase in the plume impingement can have a dramatic effect on the noise levels when the vehicle is only a few nozzle diameters from the deck. As the vehicle lifts off the deck the increase in noise levels lessens as the plume impingement increases. Several scale model acoustic tests have been undertaken at Marshall Space Flight Center which had test cases that were used to define the relationship between drift and the noise levels experienced by the vehicle.

Prediction of Acoustic Environments from Horizontal Rocket Firings

In recent years, advances in research and engineering have led to more powerful launch vehicles which yield acoustic environments potentially destructive to the vehicle or surrounding structures. Therefore, it has become increasingly important to be able to predict the acoustic environments created by these vehicles in order to avoid structural and/or component failure. The current industry standard technique for predicting launch-induced acoustic environments was developed by Eldred in the early 1970s. Recent work has shown Eldred’s technique to be inaccurate for current state-of-the-art launch vehicles. Due to the high cost of full-scale and even sub-scale rocket experiments, very little rocket noise data is available. Much of the work thought to be applicable to rocket noise has been done with heated jets. A model to predict the acoustic environment due to a launch vehicle in the far-field was created. This was done using five sets of horizontally fired rocket data, obtained between 2008 and 2012. Thro...

Acoustic contributions and characteristics of floor treatments for elementary school classroom background noise levels

A two part investigation involving the effect of floor treatments on classroom background noise levels will be presented. Phase 1 determined the effects of hard versus soft flooring on overall speech and activity noise levels using long-term calibrated sound recordings in elementary classrooms. Two similar-sized classrooms were used: one with vinyl composition tile (VCT) flooring, and one with short-pile commercial carpeting. After parsing the recordings into separate segments of (a) teacher/student speech (alone), and (b) classroom activity noise, including footfalls, chair scrapes, and impacts (no speech), a significant decrease in overall levels was found in the carpeted rooms. Phase 2 determined the acoustical properties of nine different flooring materials ranging from resilient athletic floors to VCT to commercial carpeting. Sound absorption was measured following ISO 10534-2, while ISO 3741 sound power measurements were made while either (a) using a standard tapping machine, or (b) scraping a class...

Contribution of non‐verbal and non‐ventilation noise sources to background noise levels in elementary school classrooms.

The goal of this project was to determine the effect of hard versus soft flooring on overall speech and activity noise levels in elementary classrooms. Long‐term calibrated sound recordings were measured in second and fifth grade classrooms. Within each grade level, two different classrooms were used: one with vinyl composition tile (VCT) flooring and one with short‐pile rubber‐backed commercial carpeting. The same students circulated between these rooms by grade level, providing a means of comparing sound levels generated by the same population on different floor surfaces. The VCT and carpeted classrooms had similar floor area, layout, and room volume. Recordings were edited to parse the calibrated WAV files into separate segments of (a) teacher/student speech (without other activity) and (b) classroom activity noise including footfalls, chair scrapes, and impacts (no speech). It was found that the type of flooring made a significant difference in measured activity noise. Increased levels found in the VC...

Investigations of the just-noticeable-difference of clarity index (C80)

The clarity index for music (C80) is a valuable room acoustic parameter, as it is an objective measure of how listeners perceive clarity. Knowing the just noticeable difference (JND) of C80 is of great importance to concert hall designers. Limited previous research has been conducted to find the C80 JND, and the major studies have limitations, including a small sample size. The reported JND is approximately 1 dB. An ongoing investigation is being conducted at the University of Hartford to establish the validity of these results by experimentally determining the JND, including an investigation on test method. In the first study (Ahearn etal., 2009), the subject pool was increased to 51 subjects, using test methods from prior research. The next study (Giacomoni etal., 2010) compared two C80 JND test methods, including allowing subjects to switch between signals in real-time. The results revealed the importance of subject training. In the third study (Wells etal., 2010), the switch method was used. The resulting JNDs were 1.6, 3.8, and 4.0 dB for each of the studies, respectively, showing that the C80 JND may be significantly higher than previously thought. The testing methods, results, and comparison to the previous studies will be described.

Comparison of two just‐noticeable‐difference test methods for clarity index (C80).

The just noticeable difference (JND) or smallest detectable increment of clarity index (C80) has been investigated due to the lack of consensus in the existing literature. The purpose of this study was to determine how the JND of C80 varies as a function of the test procedure. Test signals, with varying amounts of clarity, were generated and combined with short anechoic recordings of orchestral music. The testing took place in the University of Hartford’s anechoic chamber, and the signals were played back over eight spatially arranged loudspeakers. Two testing methods were compared, which both consisted of the subject hearing two signals, A and B, and deciding if the signals were the same or different in terms of clarity. For Test Method 1, the subjects were required to listen to all of signal A and then all of signal B before selecting their response. For Test Method 2, the subjects were allowed to switch between signals A and B in real‐time. The difference in the JND of C80 for the two test methods, alo...

Comparisons of different microphones, microphone orientation, and spacing on late lateral energy measurements.

A strong correlation exists between listener envelopment and late lateral energy [J. S. Bradley and G. A. Soulodre, “Objective measures of listener envelopment,” J. Acoust. Soc. Am. 98, 2590–2597 (1995)], but limited work has been conducted on measuring this parameter in actual spaces. Measuring late lateral energy (GLL) requires a figure‐of‐eight pattern microphone to measure the lateral energy only, but an omnidirectional microphone is also used simultaneously to measure other common room acoustic parameters. An investigation was conducted to determine the effects of various different microphones, microphone orientation, and the spacing between the bidirectional and omnidirectional microphone on measured GLL values. Eight figure‐of‐eight pattern microphones were used, including both ribbon [(1) Cascade Fat Head II, (2) Royer R‐121] and condenser [(2) AKG C414, (1) Neumann KM120, (2) Shure KSM44] microphones. Measurements were taken in an 80‐seat lecture‐style classroom, using the sine sweep method. The ...