Introduction: Make the Smallest Single Balanced Armature Earbuds in the World

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This is a project to make probably the smallest single BA earbuds with audiophile sound quality. The design was inspired by Final F7200, a $400+ high resolution IEM on Amazon. While with components available on the open market, DIYers can make it in 1~2h in great fun and much lower cost. (visit for all components in this project)

Compare with most commercial earbuds on the market, the key differentiation of this kit would be:

  • Extremely small (5.5mm), lightweight (23g) and durable (stainless steel) shell
  • Perfect fit and high sound isolation properties
  • Situated close to the eardrum, this earbud delivers high resolution, a vast sound stage and rich bass tones.
  • Built with similar full spectrum Balanced Armature drivers as Final F7200, manufactured in Denmark
  • Upgrade BA driver option to Knowles RAB 32257 for better bass performance
  • MMCX connectors and custom 6N silver plated OFC cable
  • Safe fit edge for silicon or foam ear-tips to protect your ear, which is also compatible with all 4.3mm ear tips you can easily buy from most markets

Step 1: Know the Components

  • 2 pcs of MMCX female connectors
  • 2 pcs stainless steel shells
  • 2 pcs of ear tips, 4.3mm inner diameter
  • 2 pcs anti-dust covers, 4.3mm diameter
  • 2 pcs BA driver housing (3D printed)
  • 2 pcs BA drivers (Knowles RAB 32257 or Sonion 26U08/9)
  • 4 pcs inner wires, 6N OFC

Step 2: Solder Wires to BA Drivers

See the +/- pin definition below of Knowles drivers. Sonion driver is the same.

And make sure you solder the blue wire to negative pin and red wire to positive pin.

Step 3: Glue Drivers to Housing

Then glue the driver to the housing. We recommend T8000/E8000/B7000 or similar instant dry glues, where you can easily find on stores nearby. And wait >30min until the glue fully dry.

Step 4: Install Drivers+housing to Shell

Follow following direction to push BA+housing in to the shell.

Apply some glue around the housing and glue it to the shell, Wait until the glue being dry, then put on the anti-dust cover.

Step 5: Install the MMCX Female Connector

Solder the blue wire to the ground pin and red wire to the positive pin, see below.

Step 6: Test and Finalize

You shall test the earbuds now before the final step to make sure all previous steps being done perfectly. The best way is to measure the FR response and ensure L/R channels being fully balanced. As both Knowles and Sonion are top BA manufactures, the channel balance can be very good (variance <1dB). If you don’t have an ICE711 coupler, you can try some familiar musics to check if bass, mid and high all sound identical from L/R earbuds. See the reference measurements I did with a IEC711 coupler and ARTA software on the Knowles RAB 32557 based kits.

  • Frequency response - Red for Left and Blue curve for Right. The 2 curves must be very close to ensure good L/R balance. As you can observed in the figure, the channel matching is nearly perfect if you make it right.
  • Impulse response - the short the better. You can see the response is within 2.5ms which is an excellent number.
  • Cumulative Spectral Decay - the decay over time and frequency shall be as consistent as possible. You can see there are peaks at 3 and 8KHz, and valley at 6KHz. Although it is not perfect, it outperforms most IEMs built with dynamic drivers.

If everything OK, apply a little bit instant dry glue to the edge of MMCX connector, and slowly screw it into the shell. Then you have this nice earbuds finally.

Step 7: About the Cable

This earbuds have to work with the cable specially customized for 2 reasons: firstly, the MMCX connector must be super tiny and light weight, second, it must be 90 degree curved. The only MMCX connector meeting these requirements are those used in Radio/RF scenarios like microwave or cable TV. You can build it by your self or order from