• Unique design minimizes interference with ERP / EP measurements
  • Predictable frequency response
  • High isolation between ears: reduces the need for masking sound (* when used with a source having separate grounds for each channel – eg NOT a standard PC sound card) 
  • Eliminates collapsed ear canal problem
  • 30+ dB external noise exclusion

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Why do I need these special earphones for auditory EP / ERP applications?

  • Calibratable – These insert earphones have optimally-flat frequency response. So, no matter the frequency of the sound you play, you can apply a single scale factor to achieve relatively accurate control of sound-pressure at the earphone.
  • Reduced stimulus artifact – The transducer is a few inches from the electrodes so for most applications you will not see a stimulus artifact in the recorded EEG. In certain applications (e.g. frequency following response), it may be necessary to externally shield the transducer to attenuate tiny electromagnetic emissions. On the plus side, these transducers are small and inline, making external shielding relatively easy.
  • Predictable timing – The time it takes for sound to travel from the transducer to the ear is exactly one millisecond, and you can take that into account in your measurements.

Can I use standard earphones or speakers?

  • Standard headphones will interfere with the EEG recording.

You can use loudspeakers, but we recommend against that because:

  • Loudspeakers can produce more stimulus artifact than small insert earphone transducers.
  • Sound pressure levels depend on the exact head position relative to the speaker.
  • Loudspeakers typically have irregular (not flat) pass bands, making calibration across frequencies a challenge.
  • Time delay from speaker to ear depends on distance and head-position, so it is impossible to know the timing delay to the ear without carefully measuring the distance between the speaker and the ear.
  • The amount of artifact may vary form one participant to the next if the location of the participant in the room relative to speakers and/or the voltage level of the signal used to accomplish nHL stimulation level vary from one participant to the next.