Vibrating systems such as the middle ear are affected by changes in ma
ss. After disease or ear surgery, significant changes in mass may cont
ribute positively or negatively to the postoperative hearing threshold
. This article describes experiments in 15 human temporal bones of the
addition or reduction of mass on the middle ear transfer function. Me
asurement of stapes and umbo vibration was performed using a Laser Dop
pler Vibrometer before and after the addition of different masses at s
everal sites on. the tympanic membrane (TM) and ossicular chain. The i
nput was 61 pure tones swept from 147 to 19433 Hz at 80 dB SPL. The ad
dition of mass onto the TM produced varying detrimental effects on sou
nd transmission, depending on the location and amount of mass. The ins
ertion of ventilation tubes, weighing 12 to 17 mg each, produced losse
s at 1.5 to 5.0 khz compared with tympanotomy alone. Addition of mass
to the umbo and malleus head produced a loss at mid and high frequenci
es, whereas addition of mass on the incus long process and stapes also
produced a high-frequency decrease in stapes displacement. Reduction
of TM mass by removal of the epithelium produced an increase, especial
ly at 2.0 to 4.0 kHz.