711 Coupler - Reference Point?

Hey there,

does anyone know what parts of the human ear the 711 coupler (60318-4 Occluded Ear Simulator) does actually simulate?
Is it the ear drum impedance and inner ear? Or does it also cover a certain length of the ear canal? EEP or DRP?

I'm working on an adapter to make the coupler fit a silicon ear which does not come with its own ear canal.

Greetings
Dr. S

 

I did some digging and found the answer in the following resources:

Presentation of the GRAS seminar at ALMA 2017
Abstract of the IEC 60318-4: 2010 paper
Paper on the 711 Ear Simulator (Type RA0045)
45BB / 45BC KEMAR Catalogue

If I'm not totally wrong here, the essence is that the coupler itself does only cover the impedance of the middle ear and inner ear. Everything else has to be simulated by adding extensions like the the new anthropometric pinna with its reproduction of the human ear canal. The reference point for the specified frequency response of the coupler (without any extension attached) appears to be right in front of the ear drum (DRP). The standard metal adapter the coupler comes with - the one that is mostly used for IEM measurements - is originally meant for calibration purposes with a piston phone. The other extensions are designed to adapt the pinna simulators, of course.

Now, thinking about an adapter for my silicon ears (front / back), the 3D model linked above will probably do the job. The canal extension is about 7 mm in length and leads conically to the entrance point of the ear canal (EEP). The opening that leads to the coupler is adjusted to fit the 7.5 mm entrance of the coupler (w/o anything screwed on). Here you can see the 3D model from below (looking from the pinna's side).
Keeping the canal short and following the shape of the ear I hope to not overdo the simulation and avoid uncontrollable resonances. That is probably the reason why GRAS keeps their ear canal quite short, as well.

Feel free to comment if you like.