Orienting an Outdoor Amphitheater Surrounded by Natural Rock Formations

Joseph Morris – jmorris@resolutgroup.com
Instagram: @resolutgroup

Resolut Group
181 E 5600 S, Suite 200
Murray, UT, 84123

Popular version of 2pAAa6 – Measurement-informed orientation of an amphitheater surrounded by natural rock formations using in-situ impulse response analysis.
Presented at the 190th ASA Meeting
Read the abstract at https://eppro01.ativ.me/web/planner.php?id=ASASPRING2026

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

A venue’s beauty may draw guests in, but the acoustic experience is what brings them back.

When attending a symphony, the first desired experience is to hear and appreciate music. Musical quality is important for design aspects of an outdoor amphitheater, especially when the design is impacted by large, natural rock formations. Maxwell Park in Hilldale, UT contains several striking, extraordinary features that naturally catch any eye. Although there’s beauty in this scenery, acoustic tests were needed to help enhance the listening experience, i.e., find the best stage direction. Because of these colossal rocks, the way the stage faces can strongly change what the audience hears.

During predesign, two realistic stage orientations were compared: a stage on the north side facing south (Figures 1-3), and a stage on the east side facing west (Figures 4-6). The orientation matters because rocks are reflective and if reflections arrive at the audience at different times and from different directions, they can smear the sound and make music feel less clear. To find the best option, four types of tests were performed at each orientation: an impulse response test (to see when echoes arrive), a “chirp” test (to check how different pitches carry and whether they interfere), a real-time analysis (to see how evenly sound spreads across the audience area), and a music listening test (to hear the real-world result). The client team, including several city officials and the architect, was on-site during testing and though graphs, tables, and data analyses are useful, hearing the difference in-person made the greatest impression.

Aerial view of an outdoor event layout with a marked stage area and audience zone in a desert-like terrain.

Figure 1: Northern Stage Design

Sound level meter mounted on a tripod in a desert clearing with towering red rock cliffs and sparse vegetation under a clear blue sky.

Figure 2: Northern Stage Simulation

Tripod with mounted sound level meter standing on a wide, dry dirt field surrounded by distant rocky hills under a clear blue sky.

Figure 3: Southern Audience Area

Aerial view of an outdoor stage and audience area marked in red near sparse vegetation.

Figure 4: Eastern Stage Design

Tripod-mounted microphone setup on a dirt path with desert shrubs and red rock cliffs in the background under a clear sky.

Figure 5: Eastern Stage Simulation

Wide view of a dirt plain with green shrubs and rugged rocky mountains under a clear blue sky.

Figure 6: Western Audience Area

From the north side, sound struck the nearby eastern rock face almost immediately and provided positive reinforcement for the direct sound. However, the sound reflecting off the western rock face arrived at a significant delay causing negative reinforcement which distorted the overall quality. Those repeated reflections, arriving at slightly different times, blurred the sound, made it harder to tell where the music was originating, and confused listeners. During the music listening test, the clients were so distracted that some initially assumed the sound equipment was the problem, calling it, “low quality”.

On the east side, the audience heard stronger direct sound, with only mild reflections from farther rock formations. Those reflections helped the sound feel full and supportive. During the music listening test, listeners described their experience as clear, impactful, more evenly heard across the area, and emotional to the music that was played. The same equipment and music were used for both orientations, but the natural rock formations from the eastern side had the greatest acoustic impact.

Measurements, figures, and charts help explain why one option performs better, but the shared, real-time listening experience made the difference. Based on that direct experience (supported by test results), the east-side stage orientation was the clear recommendation to, and accepted by, the client.

Music Features Prominently in Global Prehistoric Archaeology and Ancient Legends

Steven Waller – wallersj@yahoo.com

Rock Art Acoustics, Lemon Grove, CA, 91945, United States

Popular version of 2aMU6 – Musical Instruments Feature Prominently in Prehistoric Archaeology and Legends of Multiple Cultures
Presented at the 190th ASA Meeting
Read the abstract at https://eppro01.ativ.me/web/planner.php?id=ASASPRING2026

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

Put yourself in the place of one of your early Stone Age human ancestors. As you are devouring a bird, you see a hollow bone that the wind could blow through, so you breathe into it. Imagine your surprise when the bone comes alive with the piercing sound of a shrill whistle, and then your further astonishment when an invisible spirit responds from a cave on the other side of the canyon with the exact same whistling.

Early peoples did not understand the wave nature of sound. The complex acoustic principles that cause sound production from musical instruments were totally inexplicable; that goes double for sound repetition in the form of echoes. Examples will be given of ancient myths from cultures around the world describing magic flutes and echo spirits. These attempts to explain mysterious sounds by attributing them to supernatural entities underscore the misperception of such sounds in the past as otherworldly.

Sound producing objects – including flutes, drums, and musical bows – are often depicted in prehistoric paintings and engravings, which are typically situated in acoustically reflective environments such as caves, canyons, and cliff faces. Evidence is accumulating to support the theory that such rock art was motivated by the echoes and reverberation heard in those special acoustic environments. Results of archaeoacoustic studies will be presented relating musical instruments to the content and context of prehistoric art.

Another example of misperception of musical sounds in the distant past pertains to Stonehenge and other megalithic stone circles known by the collective term “Pipers’ Stones”, from an ancient legend of two magical pipers. Experimental data show that sound wave interference patterns from two flutes or bagpipes can cause the auditory illusion of acoustic shadows that seem to be cast from a ring of massive rocks blocking the sound, when in actuality it is merely sound wave cancellation from the two sound sources.

These examples of musical instruments featuring prominently in prehistoric archaeology and in legends of multiple cultures emphasize the importance of considering how the human mind has perceived and interpreted sounds over time, especially when studying archaeological sites.

“The Cave Spoke Back” ebook, a collection of archaeoacoustic publications by Steven J. Waller, can be accessed at https://www.dropbox.com/scl/fo/zx0sc652ybovt6ijf5nl0/AC2bHC3yQbTvF8lhWj5yhSc?rlkey=6je6s4zmgc9ygqme599q4c40x&st=62vrgw3f&dl=0

The sounds of the water music of Vanuatu

Randy Hurd – randyhurd@weber.edu

Weber State University, Department of Mechanical Engineering, Ogden, UT, 84408, United States

Additional author: John Allen

Popular version of 5aMU3 – Acoustics of the Vanuatu Water Music
Presented at the 189th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0041406

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

Women in the island nation of Vanuatu create music in a unique way. Standing waist deep in a pool, they strike the water with their hands creating a unique variety of tones (see Figure 1). While the acoustics of inanimate objects entering water (such as spheres and raindrops) have long been understood, the mechanisms governing human hand strikes have received less attention. For this study, we replicate and simplify these musical techniques in a controlled laboratory environment to analyze the physical properties—the hydrodynamics and the resulting acoustic profile—of the sounds produced.

Figure 1: Women from the Leweton Cultural Group in the Banks Islands of Vanuatu dance together while interacting with the water surface to create music. (Image courtesy of The Secrets of Vanuatu Water Music. Directed by Marc Hoeferlin, ARTE France and ZED, 2015)

To isolate and measure these effects, we recreated the water-slapping motions in a transparent water tank. We used a high-speed camera to capture the subsurface cavity formation in detail (see figure 2), and recorded the sounds with both an in-air microphone and an underwater hydrophone.

Figure 2: A series of high-speed image sequences portray simplifications of four different techniques used by the women of Vanuatu to create music. a) A flat-handed slap produces a wide and shallow entrained air cavity. b) A cup-handed slap produces a slightly deeper cavity. c) A plunge with a deep hand produces a deep cavity that collapses in the final image. d) A horizontal plowing motion entrains air behind the hand (50 ms between images).

The key finding of this work is the establishment of a direct link between the physical motion of the hand, the shape and size of the air cavity created, and the acoustic characteristics of the sound produced. We find that the way the hand interacts with the water creates different subsurface cavities and control the volume and tone of the sound produced. Even hand-shape upon impact is shown to affect the resulting tone. In essence, the research demonstrates that the tone and duration of the sound are primarily controlled by the size and shape of the entrained air cavity. The larger the cavity, the deeper and longer the resulting sound.

The women of Vanuatu are incredibly sophisticated in their approach to creating music. They manipulate the sound spectrum without needing different instruments, simply by varying parameters like hand pose, curvature, and depth of penetration. This is a powerful demonstration of how multiphase flow, water entry and acoustics can produce an enriching and aesthetically complex experience.

How do humans whistle?

Prashanth Tamilselvam – ptamilselvam@hawk.illinoistech.edu
Bluesky: @prashanth-t.bsky.social
Instagram: @prashanth_tamilselvam
Illinois Institute of Technology, Chicago, Illinois, 60616, United States

Francisco Ruiz
ruiz@illinoistech.edu
Illinois Institute of Technology,
Chicago, Illinois,60616
United States

Popular version of 4pMU15 – Experiments on the flow acoustics of Human whistling
Presented at the 189th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0041252

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

When was the last time you tried to whistle and wondered how do we make music with our mouth? For many, whistling feels effortless: purse your lips, blow, and a clear tone appears. Yet nearly half of us find it surprisingly difficult and never manage to produce more than a faint breath. Our research explores the physics behind this familiar but surprisingly complex activity.

When you whistle, the tongue rises against the roof of the mouth, leaving a small gap. The lips form a second constriction, and the space between acts as a resonant chamber, much like the tube of a flute. Pitch is controlled by moving the tongue to change the space between it and the palate. But geometry alone is not enough: we have found that only a specific combination of airflow and lip shape creates a ‘sweet spot’ leading to a stable tone. Maybe this is why so many people struggle with it.

Figure 1

In our experiments, involving orifices shaped like the hole of a donut to represent the lips, we found periodic vortices coming out (fig 1). These vortices are released at a frequency that is exactly the pitch we hear, showing that whistling is not simply blowing air but a precise coupling between the flow and the sound (fig 2a). The shape of the lips has a significant influence on the sound. Too narrow or too wide an opening suppresses the sound, and the front-to-back contour of the lips must encourage clean airflow separation (see how the non-toroidal lip geometry in fig 2b manages to whistle only within a small range of air velocity). This subtle control of lip geometry is essential for sustaining a clear, steady whistle.

Figure 2
The sound does not simply travel outward into the air. It also travels back into the mouth, where it interacts with the air coming from the lungs. This inward-traveling sound creates a feedback loop that amplifies the oscillations of the flow (fig 2c). The shear layer produced at the back of the mouth has a strong influence on how the airflow interacts with the lips. Subtle changes in this upstream shear layer either support or disrupt the formation of the vortices, and hence the sound.Difficult? It clearly is for many of us, but did you know that walruses also whistle? And they shape their lips exactly the way humans do it.We hope that understanding how humans (and walruses) whistle will help those of us who struggle with it. Meanwhile, our research is already guiding the development of a new, super-compact wind instrument that can be played without the use of hands. We call it the Flutino.Whistling may feel ordinary, but its physics is anything but simple.

Explaining the tone of two legendary jazz guitarists

Chirag Gokani – chiragokani@utexas.edu
Instagram: @chiragokani
Applied Research Laboratories and Walker Department of Mechanical Engineering
Austin, Texas 78766-9767

Preston S. Wilson (also at Applied Research Laboratories and Walker Department of Mechanical Engineering)

Popular version of 2aMU6 – Timbral effects of the right-hand techniques of jazz guitarists Wes Montgomery and Joe Pass
Presented at the 188th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0037556

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

Wes Montgomery and Joe Pass are two of the most influential guitarists of the 20th century. Acclaimed music educator and producer Rick Beato says,

Wes influenced all my favorite guitarists, from Joe Pass, to George Benson, to Pat Martino, to Pat Metheny, to John Scofield. He influenced Jimi Hendrix, he influenced Joe Satriani, Eric Johnson. Virtually every guitarist I can think of that I respect, Wes is a major, if not the biggest, influence of.

Beato similarly praises Joe Pass for his 1973 album Virtuoso, calling it the “album that changed my life”:

If there’s one record that I ever suggest to people that want to get into jazz guitar, it’s this record, Joe Pass, Virtuoso.

Part of what made Wes Montgomery and Joe Pass so great was their iconic guitar tone. Montgomery played with his thumb, and his tone was focused and warm. See, for example, “Cariba” from Full House (1962). Meanwhile, Pass played both fingerstyle and with a pick, and his tone was smooth and rich. His fingerstyle playing can be heard on “Just Friends” from I Remember Charlie Parker (1979), and his pick playing can be heard on “Dreamer (Vivo Sonhando)” from Ella Abraca Jobim (1981).

Wes Montgomery (left, Tom Marcello, CC BY-SA 2.0) and Joe Pass (right, Chuck Stewart, Public domain via Wikimedia Commons)

To better understand the tone of Montgomery and Pass, we modeled the thumb, fingers, and pick as they interact with a guitar string.

Our model for how the thumb, fingers, and pick excite a guitar string. The string’s deformation is exaggerated for the purpose of illustration.

One factor in the model is the location at which the string is excited. Montgomery played closer to the bridge of the guitar, while Pass played closer to the neck. Another important factor is the amount that the thumb, fingers, and pick slip off the string. Montgomery’s thumb delivered a “pluck” and slipped less than Pass’s pick, which delivered more of a “strike” to the string.

Simulations of the model suggest that Montgomery and Pass balanced these two factors with the choice of thumb, fingers, and pick. The focused nature of Montgomery’s tone is due to his thumb, while the warmth of his tone arises from playing closer to the bridge and predominantly plucking the string. Meanwhile, the richness of Pass’s tone is due to his pick, while its smooth quality is due to playing closer to the neck and predominantly striking the string. Pass’s fingerstyle playing falls in between the thumb and pick techniques.

Guitarists wishing to play in the style of Montgomery and Pass can adjust their technique to match the parameters of our model. Conversely, the parameters of our model can be adjusted to emulate the tone of other notable guitarists.

Notable jazz and fusion guitarists grouped by technique. The parameters of our model can be adjusted to describe these guitarists.

Our model could also be used to synthesize realistic digital guitar voices that are more sensitive to the player’s touch.

To demonstrate the effects of the right-hand technique on the tone, we offer an arrangement of the jazz standard “Stella by Starlight” for solo guitar. The thumb is used at the beginning of the arrangement, with occasional contributions from the fingers. The fingers are used exclusively from 0:50-1:10, after which the pick is used to conclude the arrangement. Knowledge of the physics underlying these techniques helps us better appreciate both the subtlety of guitar performance and the contributions of Montgomery and Pass to music.