What if your ears could blink? Chameleon is a variable hearing protection device that changes its attenuation according to the environment. It is targeted towards users in periodically loud environments—environments with significant noise exposure, but with periods of quiet—such as construction sites, factories and machine shops.
I was the product lead in this project, and played a pivotal role in all aspects of product design including defining requirements & benchmarks, designing the attenuation system, measurement circuit, and control logic, and implementing standard test procedures and analyzing the results.
To determine whether we were solving a real problem, we interviewed and surveyed over a dozen potential users working in the targeted environments. Many users admitted openly that they didn't regularly use hearing protection—even when they knew they should—because it was inconvenient and uncomfortable. If they were wearing hearing protection and needed to talk to a coworker, they would need to take the hearing protector off. Because of this tediousness, many people wouldn't put on hearing protection during the loud periods between conversation. Other reasons cited were because of comfort—standard hearing protectors can put a lot of pressure on the head and feel isolating, while earplugs can be hard to insert, especially when wearing work gloves. Findings from these interviews were corroborated by a number of academic sources, which study the comfort, and social implications of hearing protection 1 2 3 4 5 6.
From all our research we were able to define six major areas that the product should perform in, and user requirements in each. We took these categories and set benchmarks based on government standards, the behaviour of other devices and other research. Durability was also an area of concern throughout the design process, given the use environment, but it was an oversight that we never explicitly defined durability benchmarks.
|Product Attribute||User Requirement||Metric||Unit||Min||Target||Max|
|Attenuation||Shall protect against excessively loud noise||Reaction Time||ms||0||100||1000|
|Communication||Shall allow communication without removal in periods when communication is possible||Open Attenuation||NRR||-||0||6|
|Threshold to Close||dB (SPL)||77||85||90|
|Threshold to Open||dB (SPL)||50||55||65|
|Comfort||Should be comfortable to wear for a full work day||Weight||Grams||-||245||330|
|Ear should not touch inner cup||Inner height||mm||63||75||-|
|Cost||Should be competitively priced relative to similar products||Cost of Device||$||-||50||300|
|Should function for an entire workday||Operational time||Hours||8||12||-|
|Measurement Accuracy||Should accurately measure noise level||Measurement Error at 4000Hz||dBSPL||0||3|
Our first prototypes were of a measurement circuit—a system to calculate the volume in dB(A) from the mic's signal. The design of this piece was based on that of a standard noise meter. In order to have a useful dB value which represents loudness as a human ear might hear it, the incoming sound signal is put through a band-pass filter called an A-weight filter. I took a circuit design I found online for this filter, and simulated it to verify its behaviour before ordering parts. The filter behaved as expected, though it did have a constant amplitude drop of about -6dB. This is not a problem since the signal must be amplified before passing through the filter in the first place. This amplified and filtered signal is then input into the
analog read pin of an Arduino Uno. Since the positive and negative gains of the analog filter and amplifiers are known, we can easily calculate the voltage at the output of the microphone. Since the sensitivity of the microphone is given, the incoming noise level in dB(A) can be caculated. This took a little calibration since the component values and mic input voltage weren't precise. In the end we were able to get a relatively accurate measurement of the noise level reaching the microphone (verified using the app NoiSee).
I often got questions when demoing the prototype about why the filtering was implemented in analog circuitry as opposed to digitally. The answer for the first prototype is that the Arduino Uno was the only microcontroller we had access to at this point, and that I was more familiar with analog filters vs. digital filters. Once we had decided to implement the final prototype using a Teensy 3.2, which has enough processing power to do this kind of filtering (and I had become more familiar with digital filtering) I decided to keep this section of the design the same so I could spend more time working on parts of the prototype that didn't work yet.
More details coming soon
Hsu, Yeh-Liang et al. "Comfort Evaluation Of Hearing Protection", International Journal of Industrial Ergonomics, vol.33, pp. 543-551 (2004) ↩
Park, Min-Yong et. al. "An Empirical Study of Comfort Afforded by Various Hearing Protection Devices: Laboratory versus Field Results", Applied Acoustics, vol. 34, pp. 151-179 (1991) ↩
C. Stephenson and M. Stephenson, "Hearing loss prevention for carpenters: Part 1 - Using health communication and health promotion models to develop training that works", Noise and Health, vol. 13, no. 51, p. 113, 2011. ↩
D. Gower and J. Casalvi, "Speech Intelligibility and Protective Effectiveness of Selected Active Noise Reduction and Conventional Communications Headsets", Human Factors: The Journal of the Human Factors and Ergonomics Society, vol. 36, no. 2, 2016. ↩
Acton, W. J., "Effects of Ear Protection on Communication", The Annals Occupational Hygeine, vol. 10, pp. 423-429 (1967) ↩
E. H. Berger, "The Effects of Hearing Protectors on Auditory Communications", Aearo Company (1979) ↩