Sound deformation by the open ear canal (REUR)
The ear canal can be seen as a half open tube, that also contains a typical form. Just as an organ pipe contains a specific resonance by its length and diameter, the ear canal also has specific acoustic characteristics. The hearing aid specialist must realize that when you place an earmould in the ear canal, this will change the acoustic characteristics of the ear. We value the importance of this phenomenon.
By placing the end of the REM-tube close to the eardrum it is possible to measure the sound at that location. Outside the ear the sound is measured by the reference microphone. The difference between these two measurements is called the sound deformation by the form of the ear canal.
This measurement is called the Real Ear Unaided Response (or REUR) and when amplification is applied it is called REUG.
Real Ear Unaided Gain (REUG)
You can also measure the gain instead of the response. In gain it is called the REUG or Real Ear Unaided Gain.
The image opposite shows us a REUG measurement.
Location of the tube
The location of the measurement probe in the ear canal comes very accurately. The end of the probe must be placed at 5 or 6 millimeters from the eardrum to obtain a good measurement. When the end of the tube is located further away from the eardrum, this will create a deviation in the high frequency tunes. (The further the probe is away from the eardrum, the less high frequency tunes will be measured, making the measurement inaccurate.)