DIPLACUSIS or double hearing is the phenomenon of hearing the same tone at a different pitch in each ear. It is far more prevalent than formerly realized and can now be detected with considerable accuracy by expressing the degree of diplacusis as the percentage of deviation from the other ear. A person with normal hearing may have from 1% to 2% deviation of their tone perception which may vary with fatigue and exposure to noise. Tuning forks have long been used to indicate the presence of diplacusis. Variable frequency audio-oscillators permit accurate measurements for matching identical tones.
Diplacusis was first reported in 1907 by Shambaugh, Sr.,1 to be caused by a slight alteration in the mass of the delicate tectorial membrane causing it to respond in a different area than normal. He claimed that temporary "tinnitus aurium" was due to increased endolymphatic pressure whether caused by stapedial displacement, hypertension,
Albers GD, Wilson WH. DiplacusisI. Historical Review. Arch Otolaryngol. 1968;87(6):601-603. doi:10.1001/archotol.1968.00760060603009