• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

DIY Headphone Measurements - Ear Simulation?

P48

Member
Joined
Feb 7, 2019
Messages
31
Likes
20
#1
Hello everyone,

I've been planning to build my own dummy head for quite a long time now and am gradually comming closer to actually building the construct. The idea is to build a binaural microphone I can use for over ear headphone measurements (no IEMs) as much as for field recording.

The base will consist of a plastic mannequin head that is filled with compressed absorbing foam. As for the mics I will use some Primo EM172 electret capsules which are quite cheap and come with a great signal to noise and sensitivity. Linearity is decent for the price, as well. Maybe not the end of the road, but probably good enough for a hobby rig.

And then the heart of the matter: ear simulation.
I have finally found a pair of silicon ears which is somewhat average in size, realistic in shape and not too stiff. This should allow me to capture some generic pinna inteferences and directional bands. So far so good.
But what about the ear canal? Using pinna only, recording the sound somewhere in the concha cave, there will be no ear canal resonances which shape the timbre and are naturally processed by our brain trying to accomplish tonal balance.

There is a a lot of buzz around the net whether it is practically beneficial or not to model the ear canal.
Some say you can only get meaningful results when working with a state-of-the-art coupler by B&K or GRAS. Some say you can just use some generic 711 couplers from Taobao. Some say you just have to attach a plastic tube (18 to 25 mm long) to the ear to cover the fundamental resonances. And some say you don't need to worry about that at all because the canal is anatomically random anyway, shifting the resonant frequency in a unpredictable fashion.

After all, there is probably a piece of truth to all of them. But I wonder which of those options would fit best to my project.
To make it clear at this point: of course I can't reinvent the wheel or fit IEC standards and such with this rig. And I won't be so naive to expect any reliable correlation between the measured frequency response - depending on the impedance of the capsules, the flange and the coupling, the (here: random) shape of pinna and ear canal ecetera - and my personal perception. But I want try to account for the main requirements and difficulties for over ear measurements and expect a relative basis of comparison to judge overall tonal balance, changes with pads or varying case damping.

I know that there is no perfect standard, that even the recognized flagship couplers have their flaws and that there is also a lot of technical politics involved. And the more I read, the more I'm worrying about the usefulness of this rig. But I still do have hope that there is a practical solution that is good enough for the purpose and allows somewhat meaningful and repeatable results.

What are your thoughts?


Generic 711 coupler from Taobao? Plastic tube? Or just going completely without the ear canal?

I would welcome your response :)

Best wishes,
P48
 

P48

Member
Joined
Feb 7, 2019
Messages
31
Likes
20
#4
Thanks for your replies!

Custom canal:
...
Definitely not DIY.
I already considered to get my ear canals casted by an audiologist. But then I would probably have to create the custom molds and cast negatives made of silicone myself ... which is in an art of its own. On the other hand, having them made in the audiologist's lab might be too expensive.
The next question would be: How to join the silicon pinna (which is even harder to custom mold) and the ear canal together?

There would be a lot of things to master.

P48, you might be better off asking this on the Micbuilders group, it used to be on Yahoo. There are experienced mic designers and builders on it. https://groups.io/g/MicBuilders
Thanks for the tip!
I'm actually a user of that group. And I don't whether there are that much users who have experiences with ear simulators and couplers. But I might give it a try.
 
Last edited:

P48

Member
Joined
Feb 7, 2019
Messages
31
Likes
20
#6
There are quite inexpensive DIY ear mold kits out there, though I don't think they go as deep as a professional impression.
Is it for casting negatives or positives?

I do need the negative, the "outter shell" of course.
 
Last edited:

Wombat

Major Contributor
Joined
Nov 5, 2017
Messages
5,016
Likes
3,546
Location
Australia
#8

P48

Member
Joined
Feb 7, 2019
Messages
31
Likes
20
#10
Yes.
And I'm also aware of its issues. :rolleyes:


https://www.head-fi.org/threads/audio-measurements-on-a-headfi-budget.893084/

Even when you accept that the system is nowhere near an IEC standard due to the lack of an ear canal, there would still be the stiff pinna (hard silicone which does not bend with pressure) as a major flaw. I also dislike the fact that they offer no mic specs.

Thanks for the mention, though!
 
Top Bottom