Youtube Link - presentation by G.R.A.S. Sound & Vibration at Rocky Mountain Audio Festival
New occluded ear simulator consists of the modified IEC 60318-4 (711) Ear Simulator and the low-noise microphone system.
Its frequency response is very similar to that of a IEC 60318-4 standardized ear simulator. But above 10 kHz, the differences in the microphone diaphragm impedance results in substantial differences.
The traditional IEC standard coupler has a high-Q resonance around 13.5 kHz related to the length of the ear canal and the diaphragm impedance. This sharp resonance does contribute to large measurement uncertainties and in the IEC standard it is stated “Due to resonances in the acoustic transfer impedance of the occluded-ear simulator above 10 kHz, high measurement uncertainties, e.g. in the order of 10 dB, can occur in earphone responses”.
In this new occluded ear simulator, the single high-Q resonance is replaced by two balanced and more damped resonances. One is related to the length of the coupler cavity, which is the same as for the standard coupler, and the other is related to the undamped diaphragm resonance of the low noise microphone.
G.R.A.S. explained that the much lower Q of the two high frequency resonances means that new coupler can be used above 10 kHz as the uncertainties are much lower and repeatability is much improved over the standardized IEC 60318-4 artificial ear.
The noise floor of the new coupler system is close to or below the threshold of human hearing. Where the traditional artificial ear has a noise floor of 24.2 dB(A), the new coupler has its noise floor below 10.5 dB(A).
This low-noise microphone system has been developed to meet the consumer electronics industry's need for R&D testing of headphones, especially in-ear headphones with Active Noise Cancellation. Because it can measure down to and below the threshold of human hearing, it can measure the influence of the electronics on the audio response of the earphones.
G.R.A.S. explained that Its low noise floor and usability above 10 kHz means that measurement results will have a strong correlation with the subjective feedback from test persons and users.
Did the real ear transfer-function have such a massive rise above 10kHz? I know the λ/2 resonance gives you a peak around 13-14kHz, but do you have more data on that?
ReplyDeleteOnly measurements I've seen are the ones that Rasmussen and Bruel performed on their own ears; their averaged result is more conservative in peaking, as the new GRAS coupler seems to be aimed toward.
https://onedrive.live.com/redir?resid=3EB56A975EF74DA5!2232&authkey=!AFg0Z51hBPn5lys&ithint=file%2cpdf
Deletethis is the only paper that I have, which is you also mentioned at the comment. Their data looks peaky though.
I'm not sure whether the new coupler system simulates the real human ear better or not, but the obvious thing is the new coupler system will have better repeatabillity above 10kHz, compared to traditional couplers.
Due to it is the brand new product that just released this month, maybe we should wait until the IEC or professional audio society verifies this new GRAS coupler system.
Shouldn't you have received a calibration chart of your canal simulator's transfer characteristic showing its compliance with IEC 60318-4 tolerances? Can you show it?
ReplyDeleteYes, I received the chart but I can't remember where I put that. I'll show you when I find that.
DeleteSo, how far above 10khz can the new coupler measure (with good accuracy)?
ReplyDeleteI'm not sure about that because GRAS didn't told about that exactly. But at least it would be better than the tradtional IEC couplers. (IEC60711: 10kHz, IEC60318-4: 16kHz)
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