Audio Measurements on a Headfi Budget

Would you buy an expensive headphone without hearing it or seeing any measurements for it?

  • No

  • Yes, I'd buy it on the spot if Steve Guttenberg says it sounds good. He is always right.


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McMadface

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Wow.

The amount of information in your very first post is both stunning and incredible. Amazing work, and I'm really loving the level of dedication you guys have to headphone measurements. I stumbled in here as I was trying to learn more about accurately measuring headphones for a review I'm working on, of the AirPods Pro vs other well known wireless earbuds.

I'm considering going with an IEC 711 adapter + UMIK1 for measurements, as apparently the THD of these mics is far lower, and allows for proper measurement of stuff like ANC. Do any of you foresee any issues with this?
I'm currently using a UMIK-1 + 711 for measurements. The mic actually fits pretty perfectly into the coupler; however, the silicone o-ring in the coupler doesn't seem to be enough to seal in all the energy. I was getting a massive dip at around 7K and some roll-off at 50 and 14K.

It turned out that the cutouts at the tip of the mic was responsible for the leakage. I tried different ways of sealing off the leakage, and finally found a stainless steel flat washer that had the perfect inside and outside diameters. I'm still getting a little bit of roll-off at the low and high ends, but everything in between is fine. I am sure that if you remove the tip and use epoxy to seal the mic to the coupler, like the example given by @csglinux, that there would be no issues. However, you lose the ability to remove the coupler if you want to use the UMIK for room measurements. For instance, I recently used the UMIK to EQ my car.

Ultimately, the UMIK + Steel Washer + 711 is accurate enough for my purposes and really easy to use. I usually leave it plugged into my desktop, but can take it and make measurements on my phone with just a USB cable swap. If you try it out, I can send you a few of the steel washers that I got, and I would also love to see what you come up with get a good seal.
 
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psycoffman

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Sorry if it's a stupid question, but how do I order from TaoBao in the US?
 
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post-15299557
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eishyaku

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I'm currently using a UMIK-1 + 711 for measurements. The mic actually fits pretty perfectly into the coupler; however, the silicone o-ring in the coupler doesn't seem to be enough to seal in all the energy. I was getting a massive dip at around 7K and some roll-off at 50 and 14K.

It turned out that the cutouts at the tip of the mic was responsible for the leakage. I tried different ways of sealing off the leakage, and finally found a stainless steel flat washer that had the perfect inside and outside diameters. I'm still getting a little bit of roll-off at the low and high ends, but everything in between is fine. I am sure that if you remove the tip and use epoxy to seal the mic to the coupler, like the example given by @csglinux, that there would be no issues. However, you lose the ability to remove the coupler if you want to use the UMIK for room measurements. For instance, I recently used the UMIK to EQ my car.

Ultimately, the UMIK + Steel Washer + 711 is accurate enough for my purposes and really easy to use. I usually leave it plugged into my desktop, but can take it and make measurements on my phone with just a USB cable swap. If you try it out, I can send you a few of the steel washers that I got, and I would also love to see what you come up with get a good seal.
Hi Thanks for sharing guys really opened my eyes. If you dont mind me asking where did you get your 711 coupler?
 
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post-15300321
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McMadface

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Hi Thanks for sharing guys really opened my eyes. If you dont mind me asking where did you get your 711 coupler?
I got it from a friend who had an extra one. I think it's just a generic Taobao coupler.
 
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post-15305173
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earfonia

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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).

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):

ER4XR - ECM888B - Acoustic Coupler - Various Distances 0mm to 35.0mm.png


At 0mm:
ER4XR - ECM888B - Acoustic Coupler - Various Distances 0mm.png


At 7.5mm:
ER4XR - ECM888B - Acoustic Coupler - Various Distances 7.5mm.png


At 12.5mm:
ER4XR - ECM888B - Acoustic Coupler - Various Distances 12.5mm.png


At 20mm:
ER4XR - ECM888B - Acoustic Coupler - Various Distances 20.0mm.png


At 35mm:
ER4XR - ECM888B - Acoustic Coupler - Various Distances 35.0mm.png


What I've learned:

Bass response affected by the coupler volume. Smaller volume lower bass response, higher volume higher bass response.
Not only that, on my system bass response also affected by temperature. The lower the temperature the higher the bass response.

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.

Here is the mic and the DIY heat shrink coupler:
20191113_210839_tn.jpg


20191113_211037_tn.jpg 20191113_210923_tn.jpg

20191113_211021_tn.jpg 20191113_211007_tn.jpg

20191113_211533_tn.jpg 20191113_124926_tn.jpg

20191113_211916_tn.jpg
 
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post-15306017
Post #66 of 99

csglinux

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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? :wink:

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 :wink:
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/
 
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Cevisi

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Is there a more budget option
 
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Is there a more budget option
That was the whole point of this thread. A vinyl tube coupler+mic can be had for less than $50. You may even have an old dynamic mic lying around at home that you can just plug into your phone or soundcard. AudioTools (iOS) is about $20. REW is free (if you're not willing or able to donate to its developer). Even a (clone) 711 coupler can be bought for less than $100 (including shipping) these days.
 
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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.
in regard to the effective variation between a nice acoustic model and the flesh and bones version, I've read a study once that said they consistently measured resonance in the ear canal as would a theoretical model with a slightly shorter canal length(don't ask me to explain why ^_^. if I stumble upon that paper again I'll post it). of course that's only a tiny detail compared to the per listener variations we're going to encounter(and probably per ear for a same listener), but as a coupler usually follows the predicted acoustic model to a T, I guess it's possible that a closer reference plane could be needed to simulate a given ear canal length(for the elite few who happen to know what that is for themselves).

this has been, your monthly knowledge that helps nobody. sponsored by sugar pills, the pills that don't have a bad side effects, or a good one.
 
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post-15306776
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earfonia

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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.

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? :wink:

IMHO, all these measurements are accurate - they just might not be representative of the physical situation you intended :wink:
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/
The experiment with different tube length is just a study, similar to the test done by GRAS in their 783 whitepaper, figure 4 at page 5 (shown as page 6 on the paper):
https://www.gras.dk/files/783-Whitepaper.pdf

I just wanted to see what is the effect of the tube volume and length to the measurement result. Rather than spending too much time searching Google I did the experiment myself.

Regarding the bass response at different temperature, the story was, in Singapore, regular room temperature at home without air conditioning was around 29C +/- 2 degree. In my office, temperature usually around 25C. So every time I compare FR measurement of the same IEM I did at home and the measurement I did in office, using the same microphone and coupler, I notice the bass response always slightly different. So I did the experiment at home, starting at 29C, then using air conditioner bring down the temperature down to 23C. IEM was plugged to the coupler and mic untouched during the whole experiment, so no change on the IEM fitting to the coupler. And it shows bass response increases as temperature goes down. The experiment is repeatable. I have to search my folders where I keep the result, when found I will share it here. So noticeable result within 6 degree Celsius of temperature difference.

As for the Ety ER2SE world tour, yes I'm interested to compare our measurement using the same IEM. I just bought generic 711 coupler during AliExpress sale 11-11, the coupler probably arrive around end of this month (Nov 2019), it would be interesting to check the 711 coupler measurement and my DIY heat shrink coupler. Thanks for the offer! I will reply later on the thread.

Is there a more budget option
I've been experimenting using the Primo EM172 condenser mic and getting pretty good result. But need DIY to solder the mic capsule and make a suitable coupler. Just an option.
https://micbooster.com/primo-microphone-capsules/8-primo-em172.html
The pictures below showing the EM172 with short coupler. I plan to DIY a longer coupler to follow the 7.5mm x 12.4mm dimension.

20191114_082458_tn.jpg 20191114_082524_tn.jpg
 
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earfonia

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The China generic IEC60318-4 I bought from AliExpress has been delivered last week. So far I've done quite a lot of measurement with it and quite happy with the consistency. Using small Silicone ear tips and proper insertion, I can get less than 0.1 dB level matching between insertions. That is pretty impressive. Very consistent result between measurements. I use RME Babyface Pro for the audio interface using the XLR input with Rode VXLR+ to convert the 48V phantom power to 5V plugin power for the condenser mic inside the IEC60318-4 coupler. For software I use REW latest beta version.

20191124_095421a.jpg
 
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csglinux

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The China generic IEC60318-4 I bought from AliExpress has been delivered last week. So far I've done quite a lot of measurement with it and quite happy with the consistency. Using small Silicone ear tips and proper insertion, I can get less than 0.1 dB level matching between insertions. That is pretty impressive. Very consistent result between measurements. I use RME Babyface Pro for the audio interface using the XLR input with Rode VXLR+ to convert the 48V phantom power to 5V plugin power for the condenser mic inside the IEC60318-4 coupler. For software I use REW latest beta version.

Great setup - I love the Babyface Pro :)
 
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TooPoorForHiFi

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Hello is there a simple / easy to follow guide for setting up REW w/ Dayton iMM6? for someone that is clueless like me? I only want to measure for Channel Imbalance on IEMs
 
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