Sorry if it's a stupid question, but how do I order from TaoBao in the US?
Not a stupid question. Ordering from Taobao isn't as easy as ordering from Amazon. If you speak no Chinese, Google translate is your friend. You can also use the Google translate app on your phone (with the camera) to translate text from your computer screen. (At least, that works with Android phones.) One thing to watch out for... when you purchase aything, items initially just get sent to a local warehouse. After that point, you need to pay, separately, for the international shipping. Keep an eye on the site, because you won't get any notice of the arrival at the distribution center and if you leave it too long to pay for that shipping, the item will get returned to the seller. Good luck!
Wow I wish I knew about this thread earlier! Awesome post! Thanks a lot to
@csglinux and others who have shared many useful info here!
I have a lot to learn from you guys!
So far I've learning about IEM measurement using MiniDSP UMIK-1 and Superlux ECM888B measurement microphones, using DIY acoustic coupler made of heat shrink tube, Multiple layers of heat shrink tube (4-5 layers).
Nice work,
@earfonia 
Your multi-layered heat-shrink tubing couplers look quite professional. I think for most of what we want to do (comparing headphones), you've already got all the rig you'll ever need. And you're already using the world's best measurement software, IMHO. (BTW, you can use the camera (Capture) icon button to dump just an image of the plot, so you don't need to capture the entire screen or window.) I believe the average ear canal length is around 25 mm, but that's from the pinna, so a deep-insertion IEM probably requires us to subtract off the length of the IEM. But none of that's a problem as long as you're consistent from measurement to measurement.
The transfer impedance of the standard 711 couplers is: L_ZT(f)=85.08-20Log(f)+L_pmeas(f)+10Log(V^2/1260^2)
where V is the effective volume in mm^3. The V in a 711 coupler results from additional side volumes that act as resonators. But again, I'm not sure it's all that relevant, given that even the world's best(?) couplers aren't going to perfectly match your own ears. In fact, there's evidence that some of the newer hi-res couplers are even a step backwards in that regard.
Some other thoughts...
I've been experimenting different volume of the coupler, as well as different length from the Reference Plane to the Microphone.
Here is an experiment using Superlux ECM888B on various length of tube from 0mm up to 35mm (reference plane to microphone). I choose Superlux mic for this experiment due to the slim nozzle barrel, easier for me to DIY a coupler that can just slide on the barrel to simulate different length of the tube. I did this last year using Ety ER4XR (borrowed from my bro) Here is the result (referenced at 500Hz):
At 0mm:
At 7.5mm:
At 12.5mm:
At 20mm:
At 35mm:
What I've learned:
Bass response affected by the coupler volume. Smaller volume lower bass response, higher volume higher bass response.
I'm not sure I completely understand that one. I've not played with such drastic changes in simulated canal length, but haven't noted much change at all in the lower frequencies with insertion depth. Maybe at very short distances there's not enough length to support even a quarter wave of the lowest frequencies, and so you lose some resonance effects? This is just a wild guess.
Not only that, on my system bass response also affected by temperature. The lower the temperature the higher the bass response.
That one makes sense, because air density will be higher and the speed of sound will be lower. I'm surprised it's a significant effect though. Are you doing measurements in your freezer?
Mids (400Hz - 4kHz) not much affected by volume or length of the coupler as long as the length is less than 20mm.
Treble is the most difficult for accurate measurement, as the tube resonance directly affect the treble response. In this case I just look for a certain length that comparable to factory datasheet of the FR, like for example Knowles datasheet. Basically between 12-15 mm in length from my observation, for tube diameter between 6mm to 7mm.
IMHO, all these measurements are accurate - they just might not be representative of the physical situation you intended
The problem is knowing how to determine what physical situation we really intend to simulate. That's tough without doing MRI scans of our ear anatomies. It sounds like you've got the tube length about right.
BTW, if you're interested in participating?:
https://www.head-fi.org/threads/ety...phone-for-your-ears-and-your-couplers.908512/
