How Do We Know This Will Fit?

 
 
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Ergonomics, Anthropometry or more plainly.... 

How do we know that Mindset will fit?


David Doyon, May 16, 2018


Making consumer products is a challenge. Not only does it have to work and be robust, but it also needs to be pretty and ergonomic. In the case of headphones more specifically, it also needs to work equally well for everyone.

 

What does this mean?

For the Mindset headphones, working equally well means that the EEG signal quality, sound performance, and comfort need to be the same across users. For this post, we will investigate the ergonomics of the headphones.

The four main ways we’ve improved ergonomics and comfort are as follows:

Size and adjustments

  • The general shape of the headphones and ranges allow various adjustments to accommodate all users’ head.

Contact with the ears

  • One of the main reasons for discomfort in headphones is the contact it has with the ears. As a result, we've decided to minimize contact with the ear for comfort.

Weight distribution

  • We’ve selected and positioned the components to distribute the weight equally. By increasing padding and area of support along the top band we've been able reduce pressure on the head.

Materials

  • Our choice of cushion fabrics is due to it's ability to not feel warm on the touch while, still feeling pleasant on the skin.
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The scientific study of human measurements is referred to as anthropometry.

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To ensure that our designs meet both our functional and ergonomic goals, we needed a deep understanding of certain key human measurements. The scientific study of human measurements is referred to as anthropometry.

For a typical pair of headphones, the relevant human body measurements are head width, head height and size of the ear. However, since our product has electrodes and they must remain in contact with the users’ head at all times, we needed an additional key measurement: head curvature.

Here’s what our design process for the overall headphones geometry looked like:

Step 1: Acquire Anthropometric Data

The first step was to acquire anthropometric data on our key measurements. For typical measurements like width, height and ear size, we were able to directly use publicly available anthropometric data. However, for less standard measurements like head curvature, it wasn’t available for free or at an affordable price. Due to financial constraints, we had to resort to more creative solutions to seek the data that we needed.

We first tried measuring head curvature directly on individuals using contouring tools. We would take the tool and press it against people’s head to recreate the shape of their head. From there, we would draw and convert this measurement into computer models. An image of a typical contouring tool is shown below. In the end, we found it to be quite time consuming and imprecise. However, it did allow us to begin the mechanical design of the headphones.

 An example of a contouring tool. 

An example of a contouring tool. 

When the design advanced far enough that we needed more precise measurements, we’ve developed a method using online databases of MRI data to directly measure curvature on medical images. This method has proven to be quite fast and accurate. After going through this process, we generated a database of geometries representing the shape of hundreds of heads of various sizes.

 Example of a human head shape. 

Example of a human head shape. 

 

Step 2: Translate Anthropometric Data into Constraints

The next step was to translate this information into relevant constraints for our mechanical design, that is head width, head height and head curvature. As discussed before, head width and height data were already publicly available online, but measuring it again using our MRI technique allowed us to validate that the new data was comparable to more established data sources. After confirming that the results were equivalent, we had good confidence that our new curvature measurement would be accurate as well.

We imported each of the head shape into a computer-assisted drawing software. To simplify the analysis, we replaced the irregular shapes of the top of the head with a circular arc that fitted best. At the end of the process, we had generated a database of head arcs and their specific radius.

 Generated human head shape including arc and radius. 

Generated human head shape including arc and radius. 

Using all this data, we statistically calculated what shapes the headphones needed to take to fit everyone. In this case, “everyone” was defined as 90% of all the adult population. The headphones were shaped based on this analysis.

Step 3: Build Test Jigs

Until this point, it was all theoretical work. The next step was to design head jigs to test the real headphones. We ended up making 8 different heads representing extreme cases of width, height and curvature. You will find below a picture of the 3D design of those head jigs, as well as the final physical jig model that is being used to test the real headphones.

 

Step 4: Designing the Earcup Cavity

In addition to fitting on the head, one of the most important aspect of comfort in headphones is the way it touches the ear.

Our research has shown that as much as possible, contact between the headphones and the ears should be minimized. This is the reason why we decided the use a circumaural (around the ear) configuration. This means the cushion touches the side of your head, around the ear, and not the ear.

To ensure that the ear fits properly into the earcup cavity, we used the same anthropometric data approach to calculate the required space in the headphones to avoid any contacts between the ear and some solid components. For example, below is a cross-section of an older earcup viewed from the top. You can see the tip of the ear touching the back plate, which is not good! We had to fix this in a later revision.

 Cross section of a poorly fitted earcup. 

Cross section of a poorly fitted earcup. 

Wrapping Things Up

Overall, the shape of the headphones with its adjustment and the earcups were the most important aspects in establishing the ergonomics of the product. While the weight distributions and fabric choice do play an important role, they are simpler problems to deal with.

This concludes our behind-the-scenes overview of how ergonomics and comfort were designed into our product, and how we validated that the headphones will fit.

If you have any questions or are curious to dig deeper into some of the methods used, feel free to comment below.

 
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Joel Blair