How I finalized the way I measure my IEMs?

My goal was to find a cost-effective and reliable way to measure the frequency response of in-ear monitors (IEMs). Thankfully, numerous online resources provided step-by-step guidance, which helped me achieve my goal. At the end of this guide, I have provide a link to a separate page that lists all the interesting articles/videos that helped me through the journey and some of which offer detailed instructions for those who want more precise results.

I’ll outline the equipment and methodology I used for the measurement, along with links to where I purchased each component.

My intention was to establish a setup that would produce consistent results, enabling me to benchmark my IEMs, particularly budget models that may vary in quality between production batches. This way, I could establish a reliable frequency response curve for adjustments to meet my target curve and develop my target curve.

Equipment and Software

1.     IEC 60318-4 Occluded-Ear Simulator and USB Sound Card: Purchased as a bundle from Aliexpress: Aliexpress Link

2.     3.5mm Stereo Audio Male to 2 Female Headphone Mic Splitter Audio Adapter: Available on Amazon: Amazon Link

3.     Ibasso DC04 Pro Dongle DAC: Available on Aliexpress: Aliexpress Link

4.     REW-Room EQ Wizard Room Acoustics Software: A free, versatile software: REW Software

The simplest and most cost-effective method involves purchasing the IEC ear simulator with the sound card and using REW software to generate IEM frequency response curves. However, I encountered high distortion error messages from REW, so I experimented with various measurement combinations and compared the results to finalize my methodology.

I began by following Ian Fann’s excellent video, which provides a solid foundation for understanding the basic methodology, please see this video before proceeding with the rest of the article.

Rig Combinations and Analysis

I encountered a distortion error using Ian Fann’s method, so I tested five rig combinations:

1. USB: Following Ian Fann's method.

   • Audio Output: MacBook USB-C port → USB Sound Card → IEM to be tested.

   • Audio Input: IEC 60318-4 Coupler → USB Sound Card → MacBook USB-C port.

2. HP:

   • Audio Output: MacBook Headphone Jack (3.5mm) → Headphone Mic Splitter → IEM to be tested.

   • Audio Input: IEC 60318-4 Coupler → Headphone Mic Splitter → MacBook Headphone Jack (3.5mm).

3. IB HP:

   • Audio Output: MacBook USB-C port→ Ibasso DC04 Pro → IEM to be tested.

   • Audio Input: IEC 60318-4 Coupler → Headphone Mic Splitter → MacBook Headphone Jack (3.5mm).

4. IB USB:

   • Audio Output: MacBook USB-C port→ Ibasso DC04 Pro → IEM to be tested.

   • Audio Input: IEC 60318-4 Coupler → USB Sound Card → MacBook USB-C port.

5. HP USB:

   • Audio Output: MacBook Headphone Jack (3.5mm) → Headphone Mic Splitter → IEM to be tested.

   • Audio Input: IEC 60318-4 Coupler → USB Sound Card → MacBook USB-C port.

I compared the average curves from the left and right measurements in each scenario, smoothed by 1/6 and normalized at 85 dB for 1 kHz.

The graphs are depicted below:

Conclusion

• USB: Not chosen due to high distortion error.

• HP: Not chosen due to significant deviation in the lower end.

• IB HP: Not chosen due to significant deviation in the lower end.

• HP USB: Not chosen due to wavy results in the lower end.

• IB USB: Chosen as the best representation of the average of all and smooth throughout the frequency response.

Given these results, I decided to proceed with the "IB USB" combination. This marks the beginning of my journey to measure IEMs.

If you really want to go into more detailed measurements I suggest the below excellent article written by Earfonia:

https://www.audiosciencereview.com/forum/index.php?threads/earfonia-iem-measurement-setup-methodology.29559/#post-1033870

Finally, I referred to many articles and videos during this journey. I’ve decided to compile them into a separate page, which I can update as my journey progresses. Here’s the link to that page:

Interesting Articles and Videos along my Audio Journey

I encourage you to explore this page and share any other helpful resources with me. Let me know if you’d like me to add more interesting links.