Kiersten Reeser – kreeser@ara.com
Applied Research Associates, Inc.
7921 Shaffer Pkwy
Littleton, Colorado 80127
United States
Twitter: @ARA_News_Events
Instagram: @appliedresearchassociates
Additional authors:
Alexandria Podolski
William Gray
Andrew Brown
Theodore Argo
Popular version of 1pEA3 – Investigating Commercially Available Force Sensors for Bone Conduction Hearing Device Evaluation
Presented at the 187th ASA Meeting
Read the abstract at https://eppro01.ativ.me//web/index.php?page=IntHtml&project=ASAFALL24&id=3771572
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Bone conduction (BC) headphones produce sound without covering the outer ears, offering an appealing alternative to conventional headphones. While BC technologies have long been used for diagnosing and treating hearing loss, consumer BC devices have become increasingly popular with a variety of claimed benefits, from safety to sound quality. However, objectively measuring BC signals – to guide improvement of device design, for example – presents several unique challenges, beginning with measurement of the BC signal itself.
Airborne audio signals, like those generated by conventional headphones, are measured using microphones; BC signals are generated by vibrating transducers pressed against the head. These vibrations are impacted by how/where and how tightly the BC headphones are positioned on the head, and other factors including individualized anatomy.
BC devices have historically been evaluated using an artificial mastoid (Figure 1 – left), a specialized (and expensive) measurement tool that was designed to simulate key properties of the tissue behind the ear, capturing the output of selected clinical BC devices under carefully controlled measurement conditions. While the artificial mastoid’s design allows for high-precision measurements, it does not account for the variety of shapes and sizes of consumer BC devices. Stakeholders ranging from manufacturers to researchers need a method to measure the effective outputs of consumer BC devices as worn by actual listeners.
Figure 1. The B&K Artificial Mastoid (left) is the standard solution for measuring BC device output. There is a need for a sensor to be placed between the BCD and human head for real-life measurements of the device’s output.
Our team, made up of collaborators at Applied Research Associates, Inc. (ARA) and the University of Washington, is working to develop a system that can be used across a wide variety of unique anatomy, BC devices, and sensor placement locations (Figure 1 – right). The goal is to use thin/flexible sensors placed directly under BC devices during use to accurately and repeatably measure the coupling of the BC device with the head (static force) and the audio-frequency vibrations produced by the device (dynamic force).
Three low-cost force sensors have been identified, shown in Figure 2, each having different underlying technologies with potential to meet the requirements necessary to characterize BC device output. The sensors have undergone preliminary testing, which revealed that all three can produce static force measurements. However, the detectable frequencies and signal quality of the dynamic force measurements varied based on the sensing design and circuitry of each sensor. The design of the Ohmite force sensing resistor (Figure 3– left) limited the quality of the measured signal. The SingleTact force sensing capacitor (Figure 3– middle) was incapable of collecting dynamic measurements for audio signals. The Honeywell FSA was limited by its circuitry and could only partially detect the desired frequency ranges.
Figure 2. Three force-sensors were evaluated; Ohmite force-sensing resistor (left), SingleTact force-sensing capacitor (middle), and Honeywell FSA (right).
Figure 2. Three force-sensors were evaluated; Ohmite force-sensing resistor (left), SingleTact force-sensing capacitor (middle), and Honeywell FSA (right).
Further testing and development are necessary to identify whether dynamic force measurements can be improved by utilizing different hardware for data collection or implementing different data analysis techniques. Parallel efforts are focused on streamlining the interface between the BC device and the sensors to improve listener comfort.