Appeal No. 1996-1891
Application 08/058,478
[w]hile prior art approaches using acoustic
transmission lines generally teach the use of sound
absorbing material to minimize resonance phenomena
in the tube, according to the present invention the
tube is preferably hard and free of sound absorbing
material to take advantage of the resonance
phenomena in the acoustic transmission line to
achieve improved impedance match and thereby improve
power transfer between the loudspeaker driver and
the environment outside the cabinet. [Emphasis
added.] [Col. 3, lines 34-42.]
Taddeo, which shows a loudspeaker system having a shorter
labyrinth passage, discloses that it is known to provide
labyrinth speaker systems with
some form of damping or stuffing material for the
damping of undesired sound waves. In some instances
the damping material is simply in the form of a
lining inside the housing; and in other cases the
damping material is stuffed in the housing
completely to block off certain portions thereof,
such as for example portions of the labyrinth formed
in a transmission line
housing. Typical materials used in [the] past have
been wool, fiberglass and polyester fibers. Foam
materials have also been used.
The primary reasons for utilizing damping
materials in such housings are twofold. First, the
damping material is used to absorb unwanted higher
frequency sounds, such as internal reflections and
standing wave resonances between walls of the
cabinet, and to the extent that the lower
frequencies are attenuated to a much lower degree,
the damping material therefore acts as a desirable
low-pass filter. Secondly, the damping materials
are used to reduce the necessary cabinet volume. In
transmission line or labyrinth type enclosures, the
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