Archaeologists excavating a paleolithic cave site in Galilee, Israel, have found evidence that a deep-cave compound at the site may have been used for ritualistic gatherings, according to a new paper published in the Proceedings of the National Academy of Sciences (PNAS). That evidence includes the presence of a symbolically carved boulder in a prominent placement, and well as the remains of what may have been torches used to light the interior. And the acoustics would have been conducive to communal gatherings.
Dating back to the Early Upper Paleolithic period, Manot Cave was found accidentally when a bulldozer broke open its roof during construction in 2008. Archaeologists soon swooped in and recovered such artifacts as stone tools, bits of charcoal, remains of various animals, and a nearly complete human skull.
The latter proved to be especially significant, as subsequent analysis showed that the skull (dubbed Manot 1) had both Neanderthal and modern features and was estimated to be about 54,700 years old. That lent support to the hypothesis that modern humans co-existed and possibly interbred with Neanderthals during a crucial transition period in the region, further bolstered by genome sequencing.
The Manot Cave features an 80-meter-long hall connecting to two lower chambers from the north and south. The living section is near the entrance and was a hub for activities like flint-knapping, butchering animals, eating, and other aspects of daily life. But about eight stories below, there is a large cavern consisting of a high gallery and an adjoining smaller “hidden” chamber separated from the main area by a cluster of mineral deposits called speleothems.
That’s the area that is the subject of the new PNAS paper. Unlike the main living section, the authors found no evidence of daily human activities in this compound, suggesting it served another purpose—most likely ritual gatherings.
The duck-billed dinosaur Parasaurolophus is distinctive for its prominent crest, which some scientists have suggested served as a kind of resonating chamber to produce low-frequency sounds. Nobody really knows what Parasaurolophus sounded like, however. Hongjun Lin of New York University is trying to change that by constructing his own model of the dinosaur’s crest and its acoustical characteristics. Lin has not yet reproduced the call of Parasaurolophus, but he talked about his progress thus far at a virtual meeting of the Acoustical Society of America.
Lin was inspired in part by the dinosaur sounds featured in the Jurassic Park film franchise, which were a combination of sounds from other animals like baby whales and crocodiles. “I’ve been fascinated by giant animals ever since I was a kid. I’d spend hours reading books, watching movies, and imagining what it would be like if dinosaurs were still around today,” he said during a press briefing. “It wasn’t until college that I realized the sounds we hear in movies and shows—while mesmerizing—are completely fabricated using sounds from modern animals. That’s when I decided to dive deeper and explore what dinosaurs might have actually sounded like.”
A skull and partial skeleton of Parasaurolophus were first discovered in 1920 along the Red Deer River in Alberta, Canada, and another partial skull was discovered the following year in New Mexico. There are now three known species of Parasaurolophus; the name means “near crested lizard.” While no complete skeleton has yet been found, paleontologists have concluded that the adult dinosaur likely stood about 16 feet tall and weighed between 6,000 to 8,000 pounds. Parasaurolophus was an herbivore that could walk on all four legs while foraging for food but may have run on two legs.
It’s that distinctive crest that has most fascinated scientists over the last century, particularly its purpose. Past hypotheses have included its use as a snorkel or as a breathing tube while foraging for food; as an air trap to keep water out of the lungs; or as an air reservoir so the dinosaur could remain underwater for longer periods. Other scientists suggested the crest was designed to help move and support the head or perhaps used as a weapon while combating other Parasaurolophus. All of these, plus a few others, have largely been discredited.
Brumidi worked in various mediums, including frescoes. Among the issues facing conservators charged with maintaining the Capitol building frescoes is delamination. Artists apply dry pigments to wet plaster to create a fresco, and a good fresco can last for centuries. Over time, though, the decorative plaster layers can separate from the underlying masonry, introducing air gaps. Knowing precisely where such delaminated areas are, and their exact shape, is crucial to conservation efforts, yet the damage might not be obvious to the naked eye.
Acoustician Nicholas Gangemi is part of a research group led by Joseph Vignola at the Catholic University of America that has been using laser Doppler vibrometry to pinpoint delaminated areas of the Capitol building frescoes. It’s a non-invasive method that zaps the frescoes with sound waves and measures the vibrational signatures that reflect back to learn about the structural conditions. This in turn enables conservators to make very precise repairs to preserve the frescoes for future generations.
It’s an alternative to the traditional technique of gently knocking on the plaster with knuckles or small mallets, listening to the resulting sounds to determine where delamination has occurred. Once separation occurs, the delaminated part of the fresco acts a bit like the head of a drum; tapping on it produces a distinctive acoustic signature.
But the method is highly subjective. It takes years of experience to become proficient at this method, and there are only a small number of people who can truly be deemed experts. “We really wanted to put that experience and knowledge into an inexperienced person’s hands,” Gangemi said during a press briefing at a virtual meeting of the Acoustical Society of America. So he and his colleagues decided to put the traditional knocking method to the test.
Aztec death whistles don’t fit into any existing Western classification for wind instruments; they seem to be a unique kind of “air spring” whistle, based on CT scans of some of the artifacts. Sascha Frühholz, a cognitive and affective neuroscientist at the University of Zürich, and several colleagues wanted to learn more about the physical mechanisms behind the whistle’s distinctive sound, as well as how humans perceive said sound—a field known as psychoacoustics. “The whistles have a very unique construction, and we don’t know of any comparable musical instrument from other pre-Columbian cultures or from other historical and contemporary contexts,” said Frühholz.
A symbolic sound?
Human sacrifice with original skull whistle (small red box and enlarged rotated view in lower right) discovered 1987–89 at the Ehecatl-Quetzalcoatl temple in Mexico City. Credit: Salvador Guillien Arroyo, Proyecto Tlatelolco
For their acoustic analysis, Frühholz et al. obtained sound recordings from two Aztec skull whistles excavated from Tlatelolco, as well as from three noise whistles (part of Aztec fire snake incense ladles). They took CT scans of whistles in the collection of the Ethnological Museum in Berlin, enabling them to create both 3D digital reconstructions and physical clay replicas. They were also able to acquire three additional artisanal clay whistles for experimental purposes.
Human participants then blew into the replicas with low-, medium-, and high-intensity air pressure, and the ensuing sounds were recorded. Those recordings were compared to existing databases of a broad range of sounds: animals, natural soundscapes, water sounds, urban noise, synthetic sounds (as for computers, pinball machines, printers, etc.), and various ancient instruments, among other samples. Finally, a group of 70 human listeners rated a random selection of sounds from a collection of over 2,500 samples.
The CT scans showed that skull whistles have an internal tube-like air duct with a constricted passage, a counter pressure chamber, a collision chamber, and a bell cavity. The unusual construction suggests that the basic principle at play is the Venturi effect, in which air (or a generic fluid) speeds up as it flows through a constricted passage, thereby reducing the pressure. “At high playing intensities and air speeds, this leads to acoustic distortions and to a rough and piercing sound character that seems uniquely produced by the skull whistles,” the authors wrote.
University of Rochester linguist Andrew Bray started out studying the evolution of the trademark sports jargon used in hockey for his master’s thesis. For instance, a hockey arena is a “barn,” while the puck is a “biscuit.” When he would tell people about the project, however, they kept asking if he was trying to determine why American hockey players sound like “fake Canadians.” Intrigued, Bray decided to shift his research focus to find out if hockey players did indeed have distinctively Canadian speech patterns and, if so, why this might be the case.
He discovered that US hockey players borrow certain aspects of the Canadian English accent, particularly when it comes to hockey jargon. But they don’t follow the typical rules of pronunciation. In short, “American hockey players are not trying to shift their speech to sound more Canadian,” Bray said during a press briefing. “They’re trying to sound more like a hockey player. That’s why it’s most evident in hockey-specific terms.”
It’s a concept known as a “linguistic persona,” a means of communicating how one identifies—in this case, as a hockey player— through speech. Bray gave a talk about his research today at a meeting of the Acoustical Society of America in Ottawa, Canada, held in conjunction with the Canadian Acoustical Association.
Bray first had to figure out how to design a study to examine this question. “What does it even mean to sound like a ‘fake’ Canadian?” he said. The stereotypical Canadian speech patterns are well-known: pronouncing “out” as “oot,” for example, or “about” as “aboot,” not to mention adding a questioning “eh?” at the end of sentences. According to Bray, there are three common linguistic variables typical of Canadian English.
One is called the lower back merger shift, which involves lowering the tongue to pronounce the vowels in words like “bit” (ih), “bet” (eh), and “bat” (ah). The second is called Canadian raising, in which the body of the tongue is raised to pronounce the vowels in words like “tight” and “doubt.” Finally, there are the vowels in words like “bait” and “boat.” Canadians pronounce these vowels with only one configuration of the tongue, known as a monophthongal pronunciation. (If the tongue moves to a secondary configuration, that would be a diphthongal pronunciation.)
Bray thought the American players might be exhibiting some Canadian English variables in their speech but to different degrees, such that their pronunciations sounded just a wee bit off—i.e., “fake.” He opted to focus on the monophthongal component since he thought those pronunciations were likely to be the most prevalent in “fake Canadian” speech among US hockey players.
Enlarge/ Bray used to play hockey for the University of Georgia Ice Dawgs, shown here in 2016.
University of Georgia Ice Dawgs
Next, Bray had to build his own “corpus of hockey player speech” focused on American-born hockey players. That required extensive interviews with players. Professional National League Hockey (NHL) players might not have the time to participate, so he focused on the American Hockey League (AHL) and East Coast Hockey League (ECHL), narrowing his pool to four teams: the Charlotte Checkers, the Greenville Swamp Rabbits, the Rochester Americans, and the South Carolina Stingrays.
Bray played hockey for the University of Georgia Ice Dawgs, which helped him quickly establish a rapport with his subjects over their shared interest and get them talking at length about their hockey career trajectories. Among other benefits, it helped him avoid the dreaded “observer’s paradox,” in which asking someone to talk about their speech makes them self-conscious and subtly changes how they would normally talk. He collected data from 20 such interviews, conducted between 2017 and 2019, each lasting about 30 minutes.
He then turned those interviews into a database of “formants”—resonant frequencies that amplify some groups of harmonics above others in speech. Bray’s ASA presentation focused on two common vowel formants. The first formant (F1) roughly corresponds to tongue height, while the second (F2) corresponds to how far forward or retracted the tongue is during pronunciation.
In the case of “bait”-like vowel sounds, Bray found some evidence among his US hockey players of a monophthongal pronunciation (minimal tongue movement), as one would expect in Canadian English and perhaps parts of the upper Midwest, but which would not otherwise be present in American English dialects. “Boat”-like vowel sounds seemed more “pseudo-monophthongal” in nature. But when these were compared with benchmark expectations for Canadian English F1 and F2 formants, US hockey players came close but fell just a bit short of the mark. Nor are their pronunciations in line with standard American English dialects.
“This might be why they sound ‘fake,'” said Bray. “I’m arguing that this is the construction of a linguistic variant uniquely linked to hockey. It’s influenced by Canadian English, but it’s not entirely Canadian.” And the way the US players in his dataset pronounced “hockey” seems to be “an entirely novel pronunciation of a word linked to this community.” Bray suspects this influence will be relevant to his initial research on hockey slang, expecting to find that “hockey slang terms are pronounced differently than you’d expect for the other non-hockey related terms.”
Bray suspects this happens via some sort of “lexical diffusion.” At the junior league level (around 14 to 20 years of age), US players might not have these distinctive speech patterns, but their pronunciations may gradually shift over time the longer they play and pick up hockey slang terms. The more strongly they self-identify as hockey players, the more they will sound like “fake Canadians.”
Enlarge/ UNSW Sydney engineers developed a new way to make cold brew coffee in under three minutes without sacrificing taste.
University of New South Wales, Sydney
Diehard fans of cold-brew coffee put in a lot of time and effort for their preferred caffeinated beverage. But engineers at the University of New South Wales, Sydney, figured out a nifty hack. They rejiggered an existing espresso machine to accommodate an ultrasonic transducer to administer ultrasonic pulses, thereby reducing the brewing time from 12 to 24 hours to just under three minutes, according to a new paper published in the journal Ultrasonics Sonochemistry.
As previously reported, rather than pouring boiling or near-boiling water over coffee grounds and steeping for a few minutes, the cold-brew method involves mixing coffee grounds with room-temperature water and letting the mixture steep for anywhere from several hours to two days. Then it is strained through a sieve to filter out all the sludge-like solids, followed by filtering. This can be done at home in a Mason jar, or you can get fancy and use a French press or a more elaborate Toddy system. It’s not necessarily served cold (although it can be)—just brewed cold.
The result is coffee that tastes less bitter than traditionally brewed coffee. “There’s nothing like it,” co-author Francisco Trujillo of UNSW Sydney told New Scientist. “The flavor is nice, the aroma is nice and the mouthfeel is more viscous and there’s less bitterness than a regular espresso shot. And it has a level of acidity that people seem to like. It’s now my favorite way to drink coffee.”
While there have been plenty of scientific studies delving into the chemistry of coffee, only a handful have focused specifically on cold-brew coffee. For instance, a 2018 study by scientists at Thomas Jefferson University in Philadelphia involved measuring levels of acidity and antioxidants in batches of cold- and hot-brew coffee. But those experiments only used lightly roasted coffee beans. The degree of roasting (temperature) makes a significant difference when it comes to hot-brew coffee. Might the same be true for cold-brew coffee?
To find out, the same team decided in 2020 to explore the extraction yields of light-, medium-, and dark-roast coffee beans during the cold-brew process. They used the cold-brew recipe from The New York Times for their experiments, with a water-to-coffee ratio of 10:1 for both cold- and hot-brew batches. (Hot brew normally has a water-to-coffee ratio of 20:1, but the team wanted to control variables as much as possible.) They carefully controlled when water was added to the coffee grounds, how long to shake (or stir) the solution, and how best to press the cold-brew coffee.
The team found that for the lighter roasts, caffeine content and antioxidant levels were roughly the same in both the hot- and cold-brew batches. However, there were significant differences between the two methods when medium- and dark-roast coffee beans were used. Specifically, the hot-brew method extracts more antioxidants from the grind; the darker the bean, the greater the difference. Both hot- and cold-brew batches become less acidic the darker the roast.
Enlarge/ The new faster cold brew system subjects coffee grounds in the filter basket to ultrasonic sound waves from a transducer, via a specially adapted horn.
UNSW/Francisco Trujillo
That gives cold brew fans a few handy tips, but the process remains incredibly time-consuming; only true aficionados have the patience required to cold brew their own morning cuppa. Many coffee houses now offer cold brews, but it requires expensive, large semi-industrial brewing units and a good deal of refrigeration space. According to Trujillo, the inspiration for using ultrasound to speed up the process arose from failed research attempts to extract more antioxidants. Those experiments ultimately failed, but the setup produced very good coffee.
Trujillo et al. used a Breville Dual Boiler BES920 espresso machine for their latest experiments, with a few key modifications. They connected a bolt-clawed transducer to the brewing basket with a metal horn. They then used the transducer to inject 38.8 kHz sound waves through the walls at several different points, thereby transforming the filter basket into a powerful ultrasonic reactor.
The team used the machine’s original boiler but set it up to be independently controlled it with an integrated circuit to better manage the temperature of the water. As for the coffee beans, they picked Campos Coffee’s Caramel & Rich Blend (a medium roast). “This blend combines fresh, high-quality specialty coffee beans from Ethiopia, Kenya, and Colombia, and the roasted beans deliver sweet caramel, butterscotch, and milk chocolate flavors,” the authors wrote.
There were three types of samples for the experiments: cold brew hit with ultrasound at room temperature for one minute or for three minutes, and cold brew prepared with the usual 24-hour process. For the ultrasonic brews, the beans were ground into a fine grind typical for espresso, while a slightly coarser grind was used for the traditional cold-brew coffee.
Enlarge/ The bundengan (left) began as a combined shelter/instrument for duck hunters but it is now often played onstage.
There’s rarely time to write about every cool science-y story that comes our way. So this year, we’re once again running a special Twelve Days of Christmas series of posts, highlighting one science story that fell through the cracks in 2020, each day from December 25 through January 5. Today: the surprisingly complex physics of two simply constructed instruments: the Indonesian bundengan and the Australian Aboriginal didgeridoo (or didjeridu).
The bundengan is a rare, endangered instrument from Indonesia that can imitate the sound of metallic gongs and cow-hide drums (kendangs) in a traditional gamelan ensemble. The didgeridoo is an iconic instrument associated with Australian Aboriginal culture that produces a single, low-pitched droning note that can be continuously sustained by skilled players. Both instruments are a topic of scientific interest because their relatively simple construction produces some surprisingly complicated physics. Two recent studies into their acoustical properties were featured at an early December meeting of the Acoustical Society of America, held in Sydney, Australia, in conjunction with the Australian Acoustical Society.
The bundengan originated with Indonesian duck hunters as protection from rain and other adverse conditions while in the field, doubling as a musical instrument to pass the time. It’s a half-dome structure woven out of bamboo splits to form a lattice grid, crisscrossed at the top to form the dome. That dome is then coated with layers of bamboo sheaths held in place with sugar palm fibers. Musicians typically sit cross-legged inside the dome-shaped resonator and pluck the strings and bars to play. The strings produce metallic sounds while the plates inside generate percussive drum-like sounds.
Gea Oswah Fatah Parikesit of Universitas Gadja Mada in Indonesia has been studying the physics and acoustics of the bundengan for several years now. And yes, he can play the instrument. “I needed to learn to do the research,” he said during a conference press briefing. “It’s very difficult because you have two different blocking styles for the right and left hand sides. The right hand is for the melody, for the string, and the left is for the rhythm, to pluck the chords.”
Much of Parikesit’s prior research on the bundengan focused on the unusual metal/percussive sound of the strings, especially the critical role played by the placement of bamboo clips. He used computational simulations of the string vibrations to glean insight on how the specific gong-like sound was produced, and how those vibrations change with the addition of bamboo clips located at different sections of the string. He found that adding the clips produces two vibrations of different frequencies at different locations on the string, with the longer section having a high frequency vibration compared to the lower frequency vibration of the shorter part of the string. This is the key to making the gong-like sound.
This time around, Parikesit was intrigued by the fact many bundengan musicians have noted the instrument sounds better wet. In fact, several years ago, Parikesit attended a bundengan concert in Melbourne during the summer when it was very hot and dry—so much so that the musicians brought their own water spray bottles to ensure the instruments stayed (preferably) fully wet.
Enlarge/ A bundengan is a portable shelter woven from bamboo, worn by Indonesian duck herders who often outfit it to double as a musical instrument.
Gea Oswah Fatah Parikesit
“A key element between the dry and wet versions of the bundengan is the bamboo sheaths—the material used to layer the wall of the instrument,” Parokesit said. “When the bundengan is dry, the bamboo sheaths open and that results in looser connections between neighboring sheaths. When the bundengan is wet, the sheaths tend to form a curling shape, but because they are held by ropes, they form tight connections between the neighboring sheaths.”
The resulting tension allows the sheaths to vibrate together. That has a significant impact on the instrument’s sound, taking on a “twangier” quality when dry and a more of metallic gong sound when it is wet. Parikesit has tried making bundengans with other materials: paper, leaves, even plastics. But none of those produce the same sound quality as the bamboo sheaths. He next plans to investigate other musical instruments made from bamboo sheaths.“As an Indonesian, I have extra motivation because the bundengan is a piece of our cultural heritage,” Parikesit said. “I am trying my best to support the conservation and documentation of the bundengan and other Indonesian endangered instruments.”
Coupling with the human vocal tract
Meanwhile, John Smith of the University of New South Wales is equally intrigued by the physics and acoustics of the didgeridoo. The instrument is constructed from the trunk or large branches of the eucalyptus tree. The trick is to find a live tree with lots of termite activity, such that the trunk has been hollowed out leaving just the living sapwood shell. A suitably hollow trunk is then cut down, cleaned out, the bark removed, the ends trimmed, and the exterior shaped into a long cylinder or cone to produce the final instrument. The longer the instrument, the lower the pitch or key.
Players will vibrate their lips to play the didgeridoo in a manner similar to lip valve instruments like trumpets or trombones, except those use a small mouthpiece attached to the instrument as an interface. (Sometimes a beeswax rim is added to a didgeridoo mouthpiece end.) Players typically use circular breathing to maintain that continuous low-pitched drone for several minutes, basically inhaling through the nose and using air stored in the puffed cheeks to keep producing the sound. It’s the coupling of the instrument with the human vocal tract that makes the physics so complex, per Smith.
Smith was interested in investigating how changes in the configuration of the vocal tract produced timbral changes in the rhythmic pattern of the sounds produced. To do so, “We needed to develop a technique that could measure the acoustic properties of the player’s vocal tract while playing,” Smith said during the same press briefing. “This involved injecting a broadband signal into the corner of the player’s mouth and using a microphone to record the response.” That enabled Smith and his cohorts to record the vocal tract impedance in different configurations in the mouth.
Enlarge/ Producing complex sounds with the didjeridu requires creating and manipulating resonances inside the vocal tract.
Kate Callas
The results: “We showed that strong resonances in the vocal tract can suppress bands of frequencies in the output sound,” said Smith. “The remaining strong bands of frequencies, called formants, are noticed by our hearing because they fall in the same ranges as the formants we use in speech. It’s a bit like a sculptor removing marble, and we observe the bits that are left behind.”
Smith et al. also noted that the variations in timbre arise from the player singing while playing, or imitating animal sounds (such as the dingo or the kookaburra), which produces many new frequencies in the output sound. To measure the contact between vocal folds, they placed electrodes on either side of a player’s throat and zapped them with a small high frequency electric current. They simultaneously measured lip movement with another pair of electrics above and below the lips. Both types of vibrations affect the flow of air to produce the new frequencies.
As for what makes a desirable didgeridoo that appeals to players, acoustic measurements on a set of 38 such instruments—with the quality of each rated by seven experts in seven different subjective categories—produced a rather surprising result. One might think players would prefer instruments with very strong resonances but the opposite turned out to be true. Instruments with stronger resonances were ranked the worst, while those with weaker resonances rated more highly. Smith, for one, thinks this makes sense. “This means that their own vocal tract resonance can dominate the timbre of the notes,” he said.
