Popular version of paper 4aEA2, “Monitoring hardening of concrete using ultrasonic guided waves” Presented Thursday morning, Nov. 5, 2015, 8:50 AM, ORLANDO room,
170th ASA Meeting, Jacksonville, FL
Concrete is the most commonly used construction material in the world. The performance of concrete structures is largely determined by properties of fresh concrete at early ages. Concrete gains strength through a chemical reaction between water and cement (hydration), which gradually change a fluid fresh concrete mix to a rigid and hard solid. The process is called setting and hardening. It is important to measure the setting times, because you may not have enough time to mix and place concrete if the setting time is too early, while too late setting will cause delay in strength gain. The setting and hardening process is affected by many parameters, including water and cement ratio, temperature, and chemical admixtures. The standard method to test setting time is to measure penetration resistance of fresh concrete samples in laboratory, which may not represent the real condition in field.
Ultrasonic waves have been proposed to monitor the setting and hardening process of concrete by measuring wave velocity change. When concrete becomes hard, the stiffness increases, and the ultrasonic velocity also increases. The authors found there is a clear relationship between the shear wave velocity and the traditional penetration resistance. However, most ultrasonic tests measure a small volume of concrete sample in laboratory, and they are not suitable for field application. In this paper, the authors proposed an ultrasonic guided wave test method. Steel reinforcements (rebars) are used in most concrete structures. When ultrasonic guided waves propagate within rebar, they leak energy to surrounding concrete, and the energy leakage rate is proportion to the stiffness of concrete. Ultrasonic waves can be introduced into rebars from one end and the echo signal will be received at the same end using the same ultrasonic sensor. This test method has a simple test setup, and is able to monitor the concrete hardening process continuously.
Figure 2 shows guided wave echo signals measured on a 19mm diameter rebar embedded in concrete. It is clear that the signal amplitude decreases with the age of concrete (2 ~ 6 hours). The attenuation can be plotted vs. age for different cement/concrete mixes. Figure 3 shows the attenuation curves for 3 cement paste mixes. It is known that a cement mix with larger water cement ratio (w/c) will have slower strength gain, which agrees with the ultrasonic guided wave test, where the w/c=0.5 mix has lower attenuation rate. When there is a void around the rebar, energy leakage will be less than the case without a void, which is also confirmed by the test result in Figure 3.
Summary: This study presents experimental results using ultrasonic guided waves to monitor concrete setting and hardening process. It shows the guided wave leakage attenuation is proportional to the stiffness change of fresh concrete. Therefore the leakage rate can be used to monitor the concrete strength gain at early ages. This study may have broader applications in other disciplines to measure mechanical property of material using guided wave.
Figure. 1 Principle of ultrasonic guided wave test.
Figure. 2 Ultrasonic echo signals measured in an embedded rebar for concrete age of 2~6 hours.
Figure. 3 Guided wave attenuation rate in a rebar embedded in different cement pastes.
Does it sound better behind Miles Davis’ back? – What would it sound like face-to-face? Rushing through a holographic sound image of the trumpet
Franz Zotter – email@example.com
Matthias Frank – firstname.lastname@example.org
University of Music and Performing Arts Graz
Institute of Electronic Music and Acoustics (IEM)
Inffeldgasse 10/3, 8010 Graz, Austria
Popular version of paper 2pAAa4, “Challenges of musical instrument reproduction including directivity”
Presented Tuesday afternoon, November 3, 2015, 2:25 PM, Grand Ballroom 3
170th ASA Meeting, Jacksonville
In many of his concerts, Miles Davis used to play his trumpet facing away from the audience. Would it have made a difference had he faced the audience?
Unplugged acoustical instruments can feature a tremendously different timbre for different orientations. Musicians experience such effects while playing their instrument in different environments. Those lacking such experience can only learn about the so-called directivity of musical instruments from publications showing diagrams of measured timbral changes. Comprehensive publications from the nineteen sixties deliver remarkably detailed descriptions. And yet, it requires training to imagine how the timbral changes sound like by just looking at these diagrams.
In the new millennium, researchers built surrounding spheres of microphones that allow to record a holographic sound image of any musical instrument (Figure 1). This was done to get a more natural representation of instruments in virtual acoustic environments for games or computer-aided acoustic design. Alternatively, the holographic sound image can be played back in real environments using a compact spherical loudspeaker array (Figure 2).
Such a recording allows, for instance, to convey a tangible experience of how strongly the timbre and loudness of a trumpet changes with orientation. (Audio example 1) is an excerpt from a corresponding holographic sound image using 64 surrounding microphones. With each repetition of the excerpt, the recording position gradually moves from behind the instrumentalist to the face-to-face orientation.
While what was shown above was done under the exclusion of acoustical influences of the room, the new kind of holographic sound imagery is a key technology used to reproduce a fully convincing experience of a musical instrument within arbitrary rooms it is played in.
A surrounding sphere of 64 microphone was built at IEM (Fabian Hohl, 2009) to record holographic sound images of musical instruments. The photo (Fabian Hohl, 2009) shows Silvio Rether playing the trumpet.
OLYMPUS DIGITAL CAMERA
The icosahedron as a housing of 20 loudspeakers (a compact spherial loudspeaker array) was built 2006 at IEM. It is a device to play back holographic sound images of musical instruments. Currently, it is used as a new tool in computer music to project sound into rooms utilizing wall reflections from different directions.
The photo (Franz Zotter, 2010) shows the icosahedral loudspeaker during concert rehearsals.
In the example, one can clearly hear the orientation-related timbral changes of the trumpet. The short excerpt is played in 7 repetitions, each time recorded at another position, moving from behind the trumpet player to the front. The piece “Gaelforce” by Peter Graham is performed by Silvio Rether, and the recording was done by Fabian Hohl at IEM using the sphere shown in Figure 1.
Humans and animals that posses a relatively large separation between ears, compared to the wavelength of sound, utilize the delay of sound arrival between ears to sense its direction with relatively good accuracy. This approach is less effective when the separation between ears is small, such as in insects. However, the parasitic Ormia Ochracea fly is particularly adept at finding crickets by listening to their chirps, though the separation of their ears is much smaller than the wavelengths generated by the chirps. The female of this species seek out chirping crickets (see Fig. 1) to lay their eggs on, and do so with an accuracy of few degrees. The two eardrums of the fly are separated by a mere 1.5 millimeters (mm) yet it homes in on the cricket chirping with 50 times longer wavelength where the arrival time difference between ears is only a few millionths of a second. It is interesting to note that Zuk and coworkers found that “between the late 1990s and 2003, in just 20 or so cricket generations, Kauai’s cricket population had evolved into an almost entirely silent one” to avoid detection by the flies. The studies carried out on the fly’s hearing organ by Miles and coworkers in the mid-90s found that workings of the fly ears are different from that of the large species and are mechanically coupled at the middle and tuned to the cricket chirps giving them remarkable ability locate them.
Figure 1 Ormia Ochracea uses direction finding ears to locate crickets.
In this paper, we present a miniature directional sensor that was designed based on the fly’s ears, which consists of two wings connected in the middle using a bridge and fabricated using micro-electro-mechanical-system (MEMS) technology as shown in Fig. 2. The sensor is made of the same material used in making microchips (silicon) with the two wings having dimensions 1 mm x 1 mm each and thickness of less than half the width of human hair (25 micrometers). The sensor is tuned to a narrow frequency range, which depends on the size of the bridge that connects the two wings. The vibration amplitudes of the sensor wings (less than one millionth of a meter) under sound excitation was electronically probed using highly sensitive comb finger capacitors (similar to tuning capacitors employed in older radios) attached to the edges of the wings. It was found that the response of the sensor is highly directional (see Fig. 3) and matches well with the expected behavior.
Figure 2 Designed (left) and fabricated (right) directional sound sensor showing the comb finger capacitors for electronically measuring nanometer scale vibrations generated by incident sound. The size of the entire sensor is less than that of a pea.
Figure 3 Measured directional response of the sensor tuned to 1.67 kHz for a set of sound pressures down to 33 dB.
The sensor was able to detect sound levels close to that of a quite whisper 30 decibel (dB) which is thousand times smaller than the sound level generated in a typical conversation (60 dB). The sensor has many potential civilian and military applications involving localization of sound sources including explosions and gunshots.
Popular version of paper 2pABa9, “The metabolic costs of producing clicks and social sounds differ in bottlenose dolphins (Tursiops truncatus).”
Presented Tuesday afternoon, November 3, 2015, 3:15, City Terrace room
170th ASA Meeting Jacksonville
Dolphins are known to be quite vocal, producing a variety of sounds described as whistles, squawks, barks, quacks, pops, buzzes and clicks. These sounds can be tonal (think whistle) or broadband (think buzz), short or long, or loud or not. Some sounds, such as whistles, are used in social contexts for communication. Other sounds, such as clicks and buzzes, are used for echolocation, a form of active biosonar that is important for hunting fish . Regardless of what type of sound a dolphin makes in its diverse vocal repertoire, sounds are generated in an anatomically unique way compared to other mammals. Most mammals, including humans, make sound in their throats or technically, in the larynx. In contrast, dolphins make sound in their nasal cavity via two sets of structures called the “phonic lips” .
All sound production comes at an energetic cost to the signaler . That is, when an animal produces sound, metabolic rate increases a certain amount above baseline or resting (metabolic) rate. Additionally, many vociferous animals, including dolphins and other marine mammals, modify their acoustic signals in noise. That is, they call louder, longer or more often in an attempt to be heard above the background din. Ocean noise levels are rising, particularly in some areas from shipping traffic and other anthropogenic activities and this motivated a series of recent studies to understand the metabolic costs of sound production and vocal modification in dolphins.
We recently measured the energetic cost for both social sound and click production in dolphins and determined if these costs increased when the animals increased the loudness or other parameters of their sounds [4,5]. Two bottlenose dolphins were trained to rest and vocalize under a specialized dome which allowed us to measure their metabolic rates while making different kinds of sounds and while resting (Figure 1). The dolphins also wore an underwater microphone (a hydrophone embedded in a suction cup) on their foreheads to keep track of vocal performance during trials. The amount of metabolic energy that the dolphins used increased as the total acoustic energy of the vocal bout increased regardless of the type of sound the dolphin made. The results clearly demonstrate that higher vocal effort results in higher energetic cost to the signaler.
Figure 1 – A dolphin participating in a trial to measure metabolic rates during sound production. Trials were conducted in Dr. Terrie Williams’ Mammalian Physiology lab at the University of California Santa Cruz. All procedures were approved by the UC Santa Cruz Institutional Animal Care and Use Committee and conducted under US National Marine Fisheries Service permit No.13602.
These recent results allow us to compare metabolic costs of production of different sound types. However, the average total energy content of the sounds produced per trial was different depending on the dolphin subject and whether the dolphins were producing social sounds or clicks. Since metabolic cost is dependent on vocal effort, metabolic cost comparisons across sound types need to be made for equal energy sound production.
The relationship between energetic cost and vocal effort for social sounds allowed us to predict metabolic costs of producing these sounds at the same sound energy as in click trials. The results, shown in Figure 2, demonstrate that bottlenose dolphins produce clicks at a very small fraction of the metabolic cost of producing whistles of equal energy. These findings are consistent with empirical observations demonstrating that considerably higher air pressure within the dolphin nasal passage is required to generate whistles compared to clicks . This pressurized air is what powers sound production in dolphins and toothed whales  and mechanistically explains the observed difference in metabolic cost between the different sound types.
Figure 2 – Metabolic costs of producing social sounds and clicks of equal energy content within a dolphin subject.
Differences in metabolic costs of whistling versus clicking have implications for understanding the biological consequences of behavioral responses to ocean noise. Across different sound types, metabolic costs depend on vocal effort. Yet, overall costs of producing clicks are substantially lower than costs of producing whistles. The results reported in this paper demonstrate that the biological consequences of vocal responses to noise can be quite different depending on the behavioral context of the animals affected, as well as the extent of the response.
Au, W. W. L. The Sonar of Dolphins, New York: Springer-Verlag.
Cranford, T. W., et al., Observation and analysis of sonar signal generation in the bottlenose dolphin (Tursiops truncatus): evidence for two sonar sources. Journal of Experimental Marine Biology and Ecology, 2011. 407: p. 81-96.
Ophir, A. G., Schrader, S. B. and Gillooly, J. F., Energetic cost of calling: general constraints and species-specific differences. Journal of Evolutionary Biology, 2010. 23: p. 1564-1569.
Noren, D. P., Holt, M. M., Dunkin, R. C. and Williams, T. M. The metabolic cost of communicative sound production in bottlenose dolphins (Tursiops truncatus). Journal of Experimental Biology, 2013. 216: 1624-1629.
Holt, M. M., Noren, D. P., Dunkin, R. C. and Williams, T. M. Vocal performance affects metabolic rate in dolphins: implication for animals communicating in noisy environments. Journal of Experimental Biology, 2015. 218: 1647-1654.
1 ADA Acoustics & Media Consultants GmbH, Arkonastr. 45-49, D-13189 Berlin / Germany
2 University of Architecture and Urbanism “Ion Mincu”, Str. Academiei 18-20, RO-010014 Bucuresti / Romania
Popular version of paper 4aAA5, “The National Opera in Bucharest – Update of the room-acoustical properties” Presented Thursday morning, November 5, 2015, 10:35 AM, Grand ballroom 3
170th ASA Meeting, Jacksonville
The acoustics of an opera hall has changed dramatically within the last 100 years. Until the end of the 19th century, mostly horseshoe-shaped halls were built with acoustically high-absorbing wall and even floor areas. Likewise, the often used boxes had fully absorbing claddings. That way the reverberation in these venues was made low and the hall was perceived as acoustically dry, e.g. the opera hall in Milan. 100 years later, the trend shows opera halls with more live and higher reverberation, preferred now for music reproduction, e.g. Semper Opera in Dresden.
This desire to enhance the acoustic liveliness in the Opera House in Bucharest led to renovation work in 2013-2014. The Opera House was built in 1952-1953 for around 2200 spectators and it followed a so-called style of “socialist realism”. This type of architecture was popular at the time, when communism was new to Romania, and the building has therefore a neoclassical design. The house was looking inside the hall like a theatre of the late 19th century. The conditions in the orchestra pit for the musicians, as far as mutual hearing is concerned, were bad as well. So, construction works took place in order to improve room acoustical properties for musicians and audience.
Fig. 1: Opera hall after reconstruction
The acoustic task was to enhance the room acoustic properties significantly by substituting absorptive faces (as carpet, fabric wall linings, etc.) by reflective materials:
Carpet on all floor areas, upholstered back- and undersides of chairs
Textile wall linings at walls/ceilings in boxes, upholstered hand rails
Textile wall linings at balustrades, upholstered hand rails in the galleries
All the absorbing wall and ceiling parts were substituted by reflecting wood panels, the carpet was removed and a parquet floor was introduced. As a result, the sound does not fade out anymore as in an open-air theatre but spaciousness may be perceived now.
The primary and secondary structures of the orchestra pit were changed as well in order to improve mutual hearing in the pit and between stage and pit. The orchestra pit had the following acoustically disadvantageous properties:
Insufficient ratio between open and covered area (depth of opening 3.5 m, depth of cover 4.7 m)
The height within the pit in the covered area was very small.
The space in the covered area of the pit was highly overdamped by too much absorber.
Fig. 2: new orchestra pit, section
The following changes have been applied:
The ratio between open area and covered area is now better by shifting the front edge of the stage floor to the back: Depth of opening is now 5.1 m, depth of cover only 3.1 m.
The height within the pit in the covered area is increased by lowering the new movable podium.
The walls and soffit in the pit are now generally reflective, broadband absorbers can be placed variably at the back wall in the pit.
After an elaborate investigation by measurements and simulation on site a prolongation of the reverberation time of 0.2-0.3 s was reached to actual values of about 1.3 to 1.4 s.
Together with alterations of the geometric situation of pit, the acoustic properties of the hall are now very satisfactory for musicians, singers and the audience.
Beside the reverberation time, other room acoustical measures such as C80, Support, Strength, etc. have been improved significantly.
National Center for Physical Acoustics, The University of Mississippi,
1 Chucky Mullins,
University, MS, 38677
Lay language paper 4pEA4
Presented Thursday afternoon, November 5, 2015
170th ASA Meeting, Jacksonville
Within a few meters beneath the earth surface, three distinctive soil layers are formed: a top dry and hard layer, a middle moist and soft region, and a deeper zone where the mechanical strength of the soil increases with depth. The information of this subsurface soil is required for agricultural, environmental, civil engineering, and military applications. A seismic surface wave method has been recently developed to non-invasively obtain such information (Lu, 2014; Lu, 2015). The method, known as the multichannel analysis of surface wave method (MASW) (Park, et al., 1999; Xia, et al., 1999), consists of three essential parts: surface wave generation and collection (Figure 1), spectrum analysis, and inversion process. The implement of the technique employs sophisticated sensor technology, wave propagation modeling, and inversion algorithm.
“Figure 1. The experimental setup for the MASW method”
The technique makes use of the characteristic of one type of surface waves, the so-called Rayleigh waves that travel along the earth’s surface within a depth of one and a half wavelengths. Therefore the components of surface waves with short wavelength contain information of shallow soil, whereas the longer wavelength surface waves provide the properties of deep soil (Figure 2).
“Figure 2. Rayleigh wave propagation”
The outcome of the MASW method is a soil vertical profile, i.e., the acoustic shear (S) wave velocity as a function of depth (Figure 3).
“Figure 3. A typical soil profile”
By repeating the MASW measurements either spatially or temporarily, one can measure and “see” the spatial and temporal variations of the subsurface soils. Figure 4 shows a typical vertical cross-section image in which the intensity of the image represents the value of the shear wave velocity. From this image, three different layers mentioned above are identified.
“Figure 4. A typical example of soil vertical cross-section image “
Figure 5 displays another two-dimensional image in which a middle high velocity zone (red area) appears. This high velocity zone represents a geological anomaly, known as a fragipan, a naturally occurring dense and hard soil layer (Lu, et al., 2014). The detection of fragipan is important in agricultural land managements.
“Figure 5. A vertical cross-section image showing the presence of a fragipan layer”
The MASW method can also be applied to monitor weather influence on soil properties (Lu 2014). Figure 6 shows the temporal variations of the underground soil. This is a result of a long term survey conducted in 2012. By drawing a vertical line and moving it from left side to right side, i.e., along the time index number axis, the evolution of the soil profile due to weather effects can be evaluated. In particular, the high velocity zones occurred in the summer of 2012, reflecting very dry soil conditions.
“Figure 6. The temporal variations of soil profile due to weather effects”
Lu, Z., 2014. Feasibility of using a seismic surface wave method to study seasonal and weather effects on shallow surface soils. Journal of Environmental & Engineering Geophysics, DOI: 10.2113/JEEG19.2.71, Vol.19, 71–85.
Lu, Z., Wilson, G.V., Hickey, C.J., 2014. Imaging a soil fragipan using a high-frequency MASW method. In Proceedings of the Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP 2014), Boston, MA., Mar. 16-20.
Park, C.B., Miller, R.D., Xia, J., 1999. Multichannel analysis of surface waves. Geophysics, Vol. 64, 800-808.
Xia, J., Miller, R.D., Park, C.B., 1999. Estimation of near-surface shear-wave velocity by inversion of Rayleigh waves. Geophysics, Vol. 64, 691-700.