The invention provides a speaker unit for low frequency reproduction wherein
distortion is reduced and the orientation of a sound image of the lower side frequency
region is augmented. To that end, the phase characteristic in an actually used
frequency band is made substantially flat. The speaker unit includes a speaker
enclosure, a duct formed in the speaker enclosure and having a port thereon, and
a speaker mounted in the speaker enclosure. The speaker is formed such that it
has a first resonance frequency set higher than a higher side frequency of the
actually used frequency band (about 20 Hz to 100 Hz), while the port is formed
such that it has a second resonance frequency set lower than a lower side frequency
of the used frequency band. For example, the speaker includes a vibrating system
having a reduced mass or a reduced compliance with which the first resonance frequency
is set higher than the higher side frequency of the actually used frequency band,
and the duct has an increased length or a controlled cross sectional area with
which the second resonance frequency is set lower than the lower side frequency
of the actually used frequency band.
