If you are just building one of my designs, you may wish to skip this section. If you want to come up with something from scratch (or improve on my designs), it helps enormously if you can measure the frequency response in order to pinpoint issues and measure design changes.
Professional headphone manufacturers use expensive test rigs that compensate for the way the human ear alters the frequency response. If you are interested in reading more about this, I would recommend this article. If you don’t have tens of thousands of dollars lying around for a proper test rig, the one described here can be built for under US$100. It has some big limitations, but is also extremely helpful.
While I plan to make a test rig that uses a 3D printed human ear shape in order to get more accurate results, right now I am using a fairly simple flat plate. Here is my test setup:
The repeatability of the rig is not perfect, as the magnitude of the frequency response is sensitive to the location of the headphones on the rig. If there are issues with a design, it will consistently show up, so this doesn’t negate its value for diagnosing problems.
When I was exploring the effect of different design parameters, to ensure repeatability, I used bolts in a single ‘headphone’ to control the location and pressure on the cushion. This worked extremely well – the variations frequency response in the ‘baseline’ condition between tests were negligible compared to the variations from changing the design. I would recommend doing this if you are tuning a design.
The test rig was was invaluable for solving the issues I initially had with lack of high frequency response on my closed back design, so is well worth the effort if you want to tune a design or root cause issue you can hear.
Here is an example of the output, in this case my open back design vs the Grado SR225:
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