Materials selection was determined via testing. A PVC text fixture was built to test various materials and compare them relative to each other. Two phones were used to complete the testing.
Procedure
Open respective apps on phones (music player and decibel X)
Insert dB reading phone into slot near the flange plates with the bottom/microphone side inward
Insert music phone into opposite slot with the speaker inward
Begin music, dB measurement at same time. Play music (The Wreck of the Edmund Fitzgerald) for 30 seconds before stopping both simultaneously
Record the average measurement over the 30 seconds
Repeat the test three times
Remove phones
Unscrew flange plates, insert material into gap such that there is no gap between material and flange plate diameter, and retighten the bolts
Repeat steps 2-7 with new material
After all materials were tested, averages were calculated and they were compared relative to the control. The largest observed difference was found in the acoustic fabric, at 8.8 dB compared to the ridge geometry foam at 7.3 dB. See table A for detailed results.
Table C. Dampening Materials Testing Data
Fig. 1: Unscrewed flange plates with material inserted
Fig. 2: Test fixture with music phone attached
Fig. 3. Free Body Diagram of Whispr
Fig. 4. Calculations for Strap Placement
Whispr needs to be able to support its own weight while also being adjustable so that any user can wear it. This requirement is why the straps are crucial. The straps need to be placed at an ideal angle to support the mask and minimize the forces that the user experiences, while still supporting the full weight of the device and holding it steady during use.
Shown to the left in Fig. 4, and here, you can see the calculations for determining the ideal strap placement. As a team, we decided to explore the estimated force being applied to the user's head while wearing the device if the top strap was placed at an angle of 45 degrees. Yet, even with this estimate, we were not able to determine the force being applied to the user's head. While friction is being ignored, the normal force of the user's mouth pushing into the mask can not be ignored. Due to this unknown, we do not have enough information given to determine any of these values. In the future, we would perform strength tests on the straps chosen to calculate the approximate tension force. With this value, we would then calculate the ideal angle the top, load-bearing strap should be angled at in order to reduce the amount of force being put on the user's head in one contact point- allowing for maximum comfortability.
To decide which electrical components were needed, it was required to define the functions of the mask. It was determined that Whispr shall be capable of recording an individual's voice, play it back through their connected headphones, and allowing the user to switch to live monitoring. Due to these requirements, the following parts were used to achieve this goal.
Figure 4 shows the ISD1820 module used inside the outer shell of the mask. This module allows a user to record up to 10 seconds of vocal or audio input and stores it in the device until the user plays it back, or records a new sample. With this, a user is also able to switch the module to live monitoring mode, allowing the user's voice to travel back through their connected headphones with no visible audio delay. The module is powered by a 3.7V battery and powers an 8Ω speaker. This module was acquired here.
While the ISD1820 module contained buttons already, they were replaced with momentary buttons to allow the user to trigger the module from the outside of the mask. These buttons were soldered onto the board and fed through openings placed in the outer shell of the mask, allowing a user to use the functionalities of the module, without needing to remove the mask to access the module. These buttons were obtained here.
On board the module was a microphone; however, due to its placement, a user would not be able to accurately record their voice into the module while wearing the device. To fix this, the onboard microphone was desoldered and replaced with wires that ran from the leads on the module to the new location of the microphone in the outer shell, demonstrated in the PoC Prototype page. The microphone chosen can be found here.
As mentioned under ISD1820 Module, the device contained an 8Ω speaker. However, this feature was removed and instead replaced with a 3.5mm 5-pin headphone jack to allow the user to connect their headphones to the module, allowing all audio to feed into their headphones rather than their environment. This headphone jack is found here.
To power the entire circuit, a 3.7V lithium polymer battery was used. The battery used can be found here.
To connect all necessary components, a combination of jumper wires and standard 20 gauge electrical wires were used. To test the functionality of the buttons when removing and adding buttons, we used the jumper wires for quick connection tests. These wires consisted of Male-Male, Male-Female, and Female-Female connections. Once the connections were validated, we removed the jumper wires and replaced them with 20 gauge wires to finalize the connections. The jumper wires used are found here.
Fig. 5. ISD1820 module
Fig 6. Push Buttons
Fig. 7. Microphone
Fig. 8. Headphone Jack
Fig. 9. Battery
Fig 10. Jumper Wires
To size the mask according to ergonomic factors, the team utilized data from an Antropometric sizing analysis system, a study conducted by Wonsup Lee et al. This study developed a sizing analysis system for head-related product designs based on the civilian American and European Surface Anthropometry resourse database of North Americans.
For the purpose of the Whispr mask, the data utilized was 6. face width, menton to subnasale length, 22. bigonal breadth, and 27. botragion-subnasale arc.
The data was then transformed into parametric dimensions for the model and was accommodated to fit the features of the external shell and the internal dampening unit.
The team performed an Eco Audit using GRANTA software to determine Whispr's impact on the environment. We found that the vast majority of our footprint came from our materials. Almost 70% of that came from electrical components, such as the playback module and microphone. The team placed a high value on making these components easily separable from the rest of Whispr so they can be recycled once end-of-life is reached. Additionally, we made sure that the inside material of then IDU wasn't made from foam, which the manufacturing of is a source of CO2. Instead we used a fabric that is more breathable, more environmentally friendly to manufacture, and even more sound attenuating.