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Insert headphones

Microphone preamplifier

Binaural microphones

Rotating Turntable

Spherical loudspeaker

Audio stimulator for conditions with zero tolerance against electromagnetic interence

The KAR ADU insert headphones, designed by Unides Design Ay, replaces headphones / loudspeakers in surroundings where electromagnetic interference fields cannot be allowed.

The electrodynamic transducer (sound source) and the control electronics of the stimulator are enclosed in a moulded aluminum box, from which sound is transmitted via plastic / silicone tubes to a porous EAR-tip acting as an earphone. The stimulator box is placed outside the shielding room (or far away from the sensitive equipment) and only the plastic tubes conveying the sound waves are placed inside the shielding room so that no electromagnetic interference is created there. The use of replaceable EAR-tips allows 100 % hygienic use of the insert-type headphone.

The stimulator is driven by a normal sound amplifier yielding at least 100 W RMS / 8 ohm (per channel). The passive sound source requires no power supply. The KAR ADU audio stimulator is a single channel device, hence a binaural system consists of two units.

The passive ADU headphones are not digitally equalized, instead the equipment is well electro-acoustically designed so that a maximum flat frequency range is obtained. The problem with digital equalization is that it requires additional hardware whilst limiting the dynamic range of the stimulus. Also, the equalization can only be done in generic way (based on artificial ear measurements), which creates more or less artifacts in the the individual listening experience. Of course, the EAR-tips need to be properly fitted at the ear canals in order to avoid leaks that would degrade the quality of the sound reproduction and cause imperfect background noise cancellation.

KAR ADU1c & ADU2a audio stimulator

There are currently two different models of the KAR audio stimulator available. The newest design (02/2006) insert headphones are model KAR ADU1c, with a total tube length of 3.25 m.

The other model is KAR ADU2a (02/2004), with a total tube length of 5.3 m.


Download the product specifications in PDF below.


The ADU audio stimulators are in use, e.g., in the following research institutions:

Literature - reports, empirical verification

References - research

The ADU audio stimulators have been used, e.g., in the following published studies (in addition to the above):
  • Human cortical representation of 3-dimensional sounds: differences between azimuth and elevation (Nobuya Fujiki, Klaus A J Riederer, Veikko Jousmäki, Jyrki Mäkelä & Riitta Hari).
      In Society for Neuroscience 31st Annual Meeting, San Diego, CA, USA, 10.-15.11.2001.
      [Abstract in HTML]

  • Human cortical representation of virtual auditory space: Differences between sound azimuth and elevation (Nobuya Fujiki, Klaus A J Riederer, Veikko Jousmäki, Jyrki Mäkelä & Riitta Hari)
      European Journal of Neuroscience, Vol. 16, pp. 2207-2213, 2002.
      [Abstract in HTML]     [Paper in PDF]

  • Processing of sound location in human cortex (Jörg Lewald, Klaus A J Riederer, Tobias Lentz, Ingo G Meister)
      European Journal of Neuroscience, Vol. 27, pp. 1261-1270, 2008.
      [Abstract in HTML]

ADU1 audio stimulator

Model KAR ADU1c audio stimulator, 4th generation model (latest in production).