Robert D. Celmer

Computer modeling and prediction in the design of coupled volumes for a 1000‐seat concert hall at Goshen College, Indiana

The effects of specific architectural parameters (volume, shape, location, aperture size, and location) on the acoustic characteristics of variable‐acoustic coupled volumes were analyzed using the computer modeling application, CATT‐Acoustic. The purpose of the study was to optimize design and determine the effectiveness of coupled volumes for use in the Goshen College Concert Hall, Goshen, Indiana. The computer modeling technique allowed specific variables to be isolated and parameters to be analyzed. Prototype models were evaluated by a visual inspection of decay curves, comparisons of T15, T30, and T60, and auralizations. The goal was to preserve the early decay rate of the main hall while achieving a slower decay rate after 750 ms. The analysis confirmed the use of computer modeling and prediction in studying the acoustic performance of coupled volume designs. Chamber volumes were found to be the most influential factor in realizing the double‐sloped decay. Shape, location, and aperture configuration ...

Critical Bands in the Perception of Speech Signals by Normal and Sensorineural Hearing Loss Listeners

Existing auditory theory suggests a major role for critical bands. Scharf has defined the critical band empirically as “that bandwidth at which subjective responses rather abruptly change” (cf. Scharf, 1970, p. 159). In general, two stimuli separated in frequency by less than a critical bandwidth will interact in one of a number of ways, while two stimuli separated by more than a critical bandwidth will not. The critical band phenomenon has been observed in such perceptual phenomena as masking (Fletcher, 1940; Scharf, 1970), loudness (Zwicker, 1958), and musical consonance (Plomp, 1964).

Investigation of the just noticeable difference of the clarity index for music, C80.

The just noticeable difference (JND) of the clarity index for music, C80, has been reported to be approximately 1 dB, but there is limited research to support this value. A subjective study was conducted to verify this JND using a total of 51 musically trained subjects. Test signals were created using digital delays, equalizers, and reverberation‐units, and sent out to eight loudspeakers distributed throughout an anechoic chamber. Three motifs and two C80 base‐cases were tested: (1) had a C80 of −1 dB (1 kHz) with a 2.1‐s reverberation time (RT), while (2) had a C80 of +3 dB (1 kHz) with a 1.6‐s RT. Signals were presented in pairs with the first signal being the base‐case and the second having a positive difference ranging between 0.5 and 3.0 dB. Control cases with no C80 differences were also presented. Results from all 51 subjects did not reveal a clear relationship between the percentages who heard a difference versus the difference in decibels. However, when the data were filtered to include 17 of the...

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.

Higher‐order harmonic signature analysis for loudspeaker defect detection

Loudspeaker assembly faults, such as a rubbing voice coil, bent frame, loose spider, etc., have traditionally been detected using experienced human listeners at the end of a production line. Previous attempts to develop production measurement systems for on‐line testing typically analyze only low‐order harmonics for the primary purpose of measuring total harmonic distortion (THD), and thus are not specifically designed to detect defective rub, buzz, and ticking sounds. This paper describes a new method wherein the total energy of high‐order harmonics groups, for example, 10th through the 20th or 31st through the 40th, are measured and analyzed. By grouping high‐order harmonics and resolving their respective total energies, distinct signatures can be obtained that correlate to the root cause of audible rub and buzz distortions [Temme (2000)]. The paper discusses loudspeakers tested with specific defects, as well as results of a computer‐based electroacoustic measurement and analysis system used for detection.

“Sweet Spot” or “Sweet Zone”? Modal Analysis of a Wooden Baseball Bat for Design Optimization

This paper describes modal testing of a wooden baseball bat with the purpose of finding the peak frequencies and vibration modes and their relation to the so-called “sweet spot”. Initial vibration testing was done by performing a tap test along a Louisville Slugger wooden baseball bat. The bat was suspended by elastic rubber bands to approximate free-free boundary conditions. The peak frequencies and bending mode shapes of the baseball bat were obtained. To verify the results, a modal analysis of the baseball bat was performed to simulate the structure’s dynamic behavior. The animated model validated the accuracy of the parameters obtained in the tap test. The bending mode shapes were also compared to the bending elastic mode shapes of a uniform, homogeneous beam undergoing no shear distortion. The exact solution of the beam equation of motion was solved. The mode shapes were plotted to compare them with the ones obtained from the baseball bat. This comparison indicated that the bat and the beam structures presented the same type of bending mode.Copyright

A senior engineering design elective with industry and community‐sponsored noise control projects

One of the transitions that engineering students must make as they enter the work force is the progression from theoretical concepts, or book learning to applied or real world applications. At the University of Hartford, engineering design courses serve as culminating experiences devised to bridge this passage. One such course, Noise Control Design, challenges the student to apply the past three years’ conceptual base to a problem solving opportunity replete with actual scenarios encountered in industry or the community. Each year local firms and organizations approach the laboratory for assistance with a variety of sound or vibration problems. After an initial training period, students make use of the laboratory’s dual channel FFT and real time analyzers, anechoic chamber, sound intensity and modal analysis software, acoustic modeling software, vibration tables and transducers, portable sound level meters and digital tape recorders. Using a consultant‐client model, students work collaboratively in teams ...

Study of the effects of different endpin materials on cello sound characteristics

The purpose of this study was to investigate the effects of changing a cellos endpin material and boundary conditions on the sound and vibration characteristics of a cello. It was hypothesized that an endpin made of a denser material than stainless steel, which is traditionally used, would improve the tone quality of the cello. In terms of endpin boundary conditions, it was hypothesized that using a shorter endpin with fixed end conditions might also improve the vibration characteristics and sound radiation efficiency of the cello. Objective and subjective tests were conducted to examine the effects of the different endpin materials. Sound power level output and vibration measurements of a cellist playing on different endpins were obtained following ISO 3741. In general, sound power levels and measured vibrations were consistent for all endpins for all notes tested. For the subjective study, volunteer cellists played selected excerpts with the different endpins, not knowing which endpin they were using. ...

Investigation of the subjective impression of listener envelopment with both binaural recordings and auralizations.

Listener envelopment (LEV) is the sense of being fully immersed in a sound field and can be used to compare the listening experience in different concert halls. LEV has been shown to correlate with the objective parameter late lateral sound level (GLL) through the use of simulated sound fields generated with delays and reverberators. The primary purpose of this study was to investigate this correlation using both binaural recordings made in a 900‐seat hall and auralizations made in an ODEON v9.20 model with both measured and predicted GLL values. In addition, the ratings of the actual recordings and simulations were compared to determine equivalency. A subjective study was carried out using 35 musically trained test participants who rated 24 stimuli, which varied as a function of both receiver position and hall setting. The ratings of the binaural recordings were found to have a linear correlation with both the measured and simulated GLL values, while the ratings of the auralizations were not found to hav...

Using a personal computer platform to develop an information‐rich learning environment for instruction in acoustics

Teaching students the subject of acoustics involves large amounts of technical information, including equations, derivations, and example problems. It also requires the explanation of a multitude of concepts, many of which are often difficult for students to grasp and equally frustrating for the instructor to disseminate. Part of the difficulty can be traced to the use of text (a visually based medium) to teach about sound (an aurally based medium). This presentation will describe the development of multimedia techniques for in‐class presentation of acoustics instruction. Some of the materials were developed using certain authoring applications, drawing and animation programs, sound manipulation software, as well as 3D CAD and spectral analysis applets. In addition to the classroom materials, self‐paced exercises have been developed to review the material in a student‐centered learning environment, along with scheduled interaction time with the instructor for questions, clarifications, and test administra...