Insert Earphones by ER

When sounds are presented through earphones the free field characteristics of the ear are replaced by very different characteristics that are dependent on complex and unreliable interactions between the individual earphones and the individual ear. So it is better to use insert earphones for doing the tests. Here are the earphones offered by ER. I am not aware of other companies.

For research purposes ER has two headphones:

ER1 $540 http://www.etymotic.com/pro/er1.asp

This is designed to have the average free field response of the the ear.  The quater-wavelength longitudinal resonance of the ear canal between 2 and 3 kHz can be seen. Response almost flat from 3 to 11 kHz.

ER2 $825 http://www.etymotic.com/pro/er2.asp

completely Flat frequency response till 12 kHz.

ER 4 series $330 (ER 4S, 4B, 4P) http://www.etymotic.com/ephp/er4-ts.asp

The ER-4S earphone has an equalized high frequency response. This is good for listening to already equalized stereo recordings. Good earphones but not good for doing experiments.

ER 6 series $139 http://www.etymotic.com/ephp/er6-ts.asp

Cheaper alternative to ER4. Good thing about this is that the response is not equalized.

ER2 ideally has the best response. Since pinna cues are present in the fre. range 3 to 12 kHz (we ignore higher frequencies) ER1 would do. It may even be better since it simulates the ear canal resonance. Since HRIRs are measured with the blocked meatus the measure HRIR do not have the canal resonance. The canal resonance may make the stimuli sound more like in free field. If you want to buy a cheaper one ER6 would be better than ER4 since ER6 is not equalized.