A cheap earphone for small animals with good frequency response in the ultrasonic frequency range

A new type of earphone for binaural stimulation in small animals is described. The characteristic features are: (1) small, 8 mm diameter, can be miniaturised further; (2) cheap, uses no expensive condenser microphone capsule, material costs less than 20 dollars; (3) frequency response flat within 6 dB between 10 kHz and 120 kHz, within 10 dB up to 200 kHz; (4) harmonic distortions at levels of the fundamental frequency below 75 dB SPL is below - 34 dB at worst case (10 kHz); and (5) due to the low price the most stable earphones optimally paired for dichotic stimulation can be selected by screening a number of individual specimen.