<s>
An	O
acoustic	B-Architecture
transmission	I-Architecture
line	I-Architecture
is	O
the	O
use	O
of	O
a	O
long	O
duct	O
,	O
which	O
acts	O
as	O
an	O
acoustic	O
waveguide	O
and	O
is	O
used	O
to	O
produce	O
or	O
transmit	O
sound	O
in	O
an	O
undistorted	O
manner	O
.	O
</s>
<s>
Examples	O
of	O
transmission	O
line	O
(	O
TL	O
)	O
related	O
technologies	O
include	O
the	O
(	O
mostly	O
obsolete	O
)	O
speaking	O
tube	O
,	O
which	O
transmitted	O
sound	O
to	O
a	O
different	O
location	O
with	O
minimal	O
loss	O
and	O
distortion	O
,	O
wind	O
instruments	O
such	O
as	O
the	O
pipe	O
organ	O
,	O
woodwind	O
and	O
brass	O
which	O
can	O
be	O
modeled	O
in	O
part	O
as	O
transmission	O
lines	O
(	O
although	O
their	O
design	O
also	O
involves	O
generating	O
sound	O
,	O
controlling	O
its	O
timbre	O
,	O
and	O
coupling	B-Application
it	O
efficiently	O
to	O
the	O
open	O
air	O
)	O
,	O
and	O
transmission	B-Architecture
line	I-Architecture
based	I-Architecture
loudspeakers	I-Architecture
which	O
use	O
the	O
same	O
principle	O
to	O
produce	O
accurate	O
extended	O
low	O
bass	O
frequencies	O
and	O
avoid	O
distortion	O
.	O
</s>
<s>
The	O
complex	O
loading	O
of	O
the	O
bass	O
drive	O
unit	O
demands	O
specific	O
Thiele-Small	B-Device
driver	I-Device
parameters	I-Device
to	O
realise	O
the	O
full	O
benefits	O
of	O
a	O
TL	O
design	O
.	O
</s>
<s>
Acoustic	B-Architecture
transmission	I-Architecture
lines	I-Architecture
gained	O
attention	O
in	O
their	O
use	O
within	O
loudspeakers	O
in	O
the	O
1960s	O
and	O
1970s	O
.	O
</s>
<s>
TDL	O
's	O
1980s	O
reference	O
speaker	O
range	O
(	O
now	O
discontinued	O
)	O
contained	O
models	O
with	O
frequency	O
ranges	O
of	O
20Hz	O
upwards	O
,	O
down	O
to	O
7Hz	O
upwards	O
,	O
without	O
needing	O
a	O
separate	O
subwoofer	B-Application
.	O
</s>
