I’m doing some research into the bone conduction of recorded and live sound through body contact with various hard surfaces, such as wood or metal. Making its way through human bone to the inner ear. This is for a creative, research project with a focus on vibratory phenomena. In this case it could also be representative of the overall equilibrium of an acoustic environment both internally and externally (to and of that environment).
In April 2021 Solange Kershaw and I produced a sound and video installation using bone conduction. The works was titled rainFalls and was produced for the Sculpture at Scenic World outdoor exhibition in Katoomba. Below is a working sketch of the audio hand rail we had fabricated for the install. It was placed in and amongst a constructed walkway surrounded by the flora and fauna in a rainforest adjacent to the world heritage listed wilderness in the Blue Mountains of NSW, Australia.
Creating and installing an audio-visual work for and in this environment was a significant challenge. Sculpture at Scenic World had not previously installed work using our particular video projection and sound technologies. They had a very skilled installation crew managed by Justin Morrissey and on this project we worked closely with Clytie Smith, all of whom were up for a challenge.
rainFalls was installed in a location based outdoor environment for a month with a large audience passing through every day to experience a range of sculptural works on display along the wilderness walkway. Our installation worked reasonably well but for me lacked sonic and visual clarity (particularly in the mid to high frequencies, 90 to 200Hz and the laser projection of water onto the surrounding trees). The overall experience of sound travelling through the elbow to the inner ear through bone conduction was not as clear or profound as I would have hoped. Ideally people engaging with the work would have experienced a unique change, shift or movement in their immediate sonic environment. If the sound coming from our installation was not transmitted in the air and through the middle ear but instead through the skull bone and inner ear it would have been a sonic experience most people (unless familiar with modern hearing aids) might never have experienced before.
The visitor’s body could act as their personal resonator with their body (size and mass) affecting the level and intensity of the audio perceived and/or heard. Ideally, when someone leant onto the railing and cupped their ears with their open hands the sound of rain & thunder was clearly conducted from the audio system on the railing, through their elbows, arms and hands and directly into their inner ear. The key word here is clearly …. Bone conduction using this technique is not necessarily that effective (for my purposes) and I am looking at other technologies that might have a more direct and effective contact with bone. The cupping of hands over ears to hear the sound transmitted from the bone in the arm and elbow also suggests that some or all of the sound is heard through air conduction and not bone conduction.
To amplify and trigger other air conducted sound we used a small 60W mono, outdoor speaker mounted above the hand rail and equipped with a Maxbotix Range Finder Ultrasonic sensor, an Arduino Uno R3 (see sketch above) and a recording of the mid to high pitched sound of just rain. This was triggered by close proximity and accompanied the bone conduction audio but transmitted in the air. It attracted people sonically to the railing and augmented the very low pitched sounds of thunder coming up through the elbows. This device failed to work about half way through the install so it was dismantled. We were unable to either fix or replace it in the short time we had left for the installation.
The video projection of large, slow drops of blueish water dripping all over the forest of trees (set in front of the elbow/sound rail) was also problematic in that the trees and space in between them were simply too bright to project into/onto. We installed the work at the top of and possibly the brightest part of the walkway and it should have been installed deep in the darkest wilderness environment possible. We had a custom built Projector enclosure (IP65 rated), which Included 2 x Fan ventilation and a glass lens cover made up for us by Andy McIntyre at illuminart. This housed an Epson EB-L610U LCD High Brightness Full HD Laser Projector and a Raspberry Pi Model B+, Power supply, Micro SD Card with QuickTime video file (shown below). The video technology could not have been better and worked without fault throughout the entire period of installation. In this writing I am not particularly focused on the video content and projection for the rainFalls installation and do not mention it again.
To transmit the sound through the elbow, arm and hand to the skull bone, the railing is equipped with bone conduction transducers, amplifiers and the input signal from a recording of rain and thunder. The audio technology we used for the sound component of the installation came from Wagner Electronics and included: A 200W Bass-Shaker Bridgeable Stereo Amplifier with remote (BSA-200). Ideal for exciters and sub sonic transducers from the Dayton Bass Shaker; 2 x Dayton 100mm Tactile Bass Shakers (BST-1); 2 x Dayton 100mm Sound Exciters 50W (HDN-8) and a looped digital audio file (rain & thunder) on a small compact audio player (placed inside a separate amplifier enclosure).
The following image is of the heavy duty metal stand with 2 speaker enclosures (amplifier is separate) that we had fabricated for the Scenic World install by Bradley Allen-Waters. The dimensions are 1300mm w x 100mm H, which made it comfortable for the average person, of average height to lean their elbows onto the top horizontal bar of the railing and cup their ears in their hands to hear the sound.
How could this concept, design and use of technology be applied to an indoor/outdoor installation and possible performance environment? The technology and sculptural work would not have to be weatherproof, power would be more accessible, the control over illumination and projection would be far greater. If for example one of the sound sources were to be large, tuned, hanging (and possibly swinging) aluminium bars and the sound from these is heard in the space, how does this accompany or work with silent sound sources that are only heard through bone conduction? Possibly by creating rooms within rooms that are connected by the extended use of internal staircases, hand-rails and furniture, such as very long interconnecting tables? A small acoustic anechoic chamber could be built within which sound(s) are produced and broadcast but then what relationship does this source of sound have to the bone conducting listener in another room. Is there a kinetic narrative developing here?
Other research activity
My early research into some practical installation art related examples of similar work includes Laurie Anderson, The Handphone Table (1978). A work that transforms the human body into a listening device using bone conduction to tell intimate stories and play songs inside one’s body [see: Google Arts & Culture reference] and The Museum of Modern Art Press Release reference], which states that: The viewer hears Laurie Anderson’s Handphone Table only while seated, elbows making contact with particular points of the table top and hands covering the ears. The viewer’s arms serve as conductors for the otherwise inaudible sound, which consists of vocal tones at one end of the table and instrumental music at the other. As a self-contained structure made with untraditional materials, the work is representative of contemporary interest in perceptual alternatives in art. There are plenty of images on Google and Pinterest of this work including this description/sketch of how it works, signed by Laurie Anderson.
A work by Markus Kison Touched Echo (2007 – 2009). Silent and Invisible WWII Memorials using BONE CONDUCTION. The touched echo installation transmits sounds of the cities which were devastated in the 1945 carpet bombing in the Second World War, through the arms of the visitors when they rest their elbows on the balustrade and hold their ears closed. Several custom-made sound conductors mounted to the railing send sounds of airplanes and bombs exploding through vibrations; it is completely silent unless you touch the railing ….
BONE CONDUCTION – How it works?
Quoted from Wikipedia – Bone conduction is the conduction of sound to the inner ear (cochlea) primarily through the bones of the skull, allowing the hearer to perceive audio content without blocking the ear canal. Bone conduction transmission occurs constantly as sound waves vibrate bone, specifically the bones in the skull, although it is hard for the average individual to distinguish sound being conveyed through the bone as opposed to the sound being conveyed through the air via the ear canal. Intentional transmission of sound through bone can be used with individuals with normal hearing — as with bone conduction headphones — or as a treatment option for certain types of hearing impairment. Bone generally conveys lower frequency sounds better than higher frequency sounds.
Other commercial headphone research
SHOKZ is a company that produces a consumer stereo bone conduction headset called Aftershokz. The outer-ear headphones have two transducers that fit slightly outside of and in front of both ears sitting on the side of the cheekbones. On their US website the description they provide for HOW IT WORKS is as follows:
Unlike traditional in-ear or on-ear headphones that utilize air conduction, Shokz（Named AfterShokz) has mastered the natural phenomenon of bone conduction by adapting it to consumer electronics, and it’s now the secret behind the success of our open-ear product line. Here’s how we’ve harnessed bone conduction technology to work for our products:
1. Audio Enters The Transducer
Every Shokz audio device features two transducers on either side. These transducers, positioned near the cheekbone, work to convert audio signals into mechanical energy (vibrations) which is then sent to your cheekbones.
2. Titanium Makes Conduction Seamless
The use of titanium in the frame of all Shokz products is not only because of its lightweight and flexible properties, but also because titanium is an ideal metal for properly and efficiently conducting sound waves.
3. Vibrations Are Converted Into Audible Sound
Advances in bone conduction technology have enabled us to create devices that minimize the sensation of vibrations on the temple while still retaining high-quality sound.
My personal experience
I have recently experienced some hearing loss, particularly in my right ear. My GP suggested using the Shokz headphones and not the earbuds I am used to. I bought a pair and have been using them for a couple of months now. They work well enough but for me lack frequency response in the lower bass register and the volume levels are not nearly as dynamic as other headphones. A newer, 9th generation bone conduction (Shokz TurboPitch™️) technology has a built-in CoreCushion low frequency enhancement unit, which they say makes music sound deeper and richer while also making the human voice sound softer and more natural during calls. I am yet to use these. In the studio I also work with over ear headphones and recently started using a pair of TMA-2 Studio Wireless+ I AIAIAI headphones, which are a professional pair of modular, versatile bluetooth headphones. This gives me a good, accurate listening experience to compare with, when listening through other air or bone conduction technologies. Some of my music and sound design background has been working with very talented sound engineers in unique and very well equipped recording studios. This has brought another level and focus for me to the detail and finer points of sound, acoustic and/or other creativity applications for audio production.
More statements & questions
Apart from the above mentioned headphone technology and the bone conduction projects I have written about what are some other examples of the effective use of bone conduction?
The human skull conducts lower frequencies better than air so people perceive their own voices to be lower and fuller than others do.
If you place the stem of a vibrating tuning fork in your mouth between your back teeth you hear the note via bone conduction.
Some animals, such as elephants pick up good vibrations through their feet. Article by Mark Shwartz for the Stanford News Service. Quote: “When an elephant transmits airborne low-frequency (20 hertz) vocalizations,” she wrote, “a corresponding seismic wave is transmitted in the ground.”
Quoted from Wikipedia: Comparison of hearing sensitivity through bone conduction and directly through the ear canal can aid audiologists in identifying pathologies of the middle ear—the area between the tympanic membrane (ear drum) and the cochlea (inner ear). If hearing is markedly better through bone conduction than through the ear canal (air-bone gap), problems with the ear canal (e.g. ear wax accumulation), the tympanic membrane or ossicles can be suspected.
If you have an interesting experience with bone conduction that you would like to share, comments on this post will be open soon … (note: these comments are moderated).