<s>
A	O
loudspeaker	B-Device
enclosure	I-Device
or	O
loudspeaker	B-Device
cabinet	I-Device
is	O
an	O
enclosure	O
(	O
often	O
rectangular	O
box-shaped	O
)	O
in	O
which	O
speaker	B-Device
drivers	I-Device
(	O
e.g.	O
,	O
loudspeakers	O
and	O
tweeters	B-Device
)	O
and	O
associated	O
electronic	O
hardware	O
,	O
such	O
as	O
crossover	B-Algorithm
circuits	I-Algorithm
and	O
,	O
in	O
some	O
cases	O
,	O
power	O
amplifiers	O
,	O
are	O
mounted	O
.	O
</s>
<s>
Enclosures	O
may	O
range	O
in	O
design	O
from	O
simple	O
,	O
homemade	O
DIY	O
rectangular	O
particleboard	O
boxes	O
to	O
very	O
complex	O
,	O
expensive	O
computer-designed	O
hi-fi	O
cabinets	O
that	O
incorporate	O
composite	O
materials	O
,	O
internal	O
baffles	O
,	O
horns	B-Device
,	O
bass	O
reflex	O
ports	O
and	O
acoustic	O
insulation	O
.	O
</s>
<s>
Loudspeaker	B-Device
enclosures	I-Device
range	O
in	O
size	O
from	O
small	O
"	B-Device
bookshelf	I-Device
"	I-Device
speaker	I-Device
cabinets	O
with	O
woofers	B-Device
and	O
small	O
tweeters	B-Device
designed	O
for	O
listening	O
to	O
music	O
with	O
a	O
hi-fi	O
system	O
in	O
a	O
private	O
home	O
to	O
huge	O
,	O
heavy	O
subwoofer	B-Device
enclosures	I-Device
with	O
multiple	O
or	O
even	O
speakers	O
in	O
huge	O
enclosures	O
which	O
are	O
designed	O
for	O
use	O
in	O
stadium	O
concert	O
sound	O
reinforcement	O
systems	O
for	O
rock	O
music	O
concerts	O
.	O
</s>
<s>
The	O
primary	O
role	O
of	O
the	O
enclosure	O
is	O
to	O
prevent	O
sound	O
waves	O
generated	O
by	O
the	O
rearward-facing	O
surface	O
of	O
the	O
diaphragm	B-Device
of	O
an	O
open	O
speaker	B-Device
driver	I-Device
interacting	O
with	O
sound	O
waves	O
generated	O
at	O
the	O
front	O
of	O
the	O
speaker	B-Device
driver	I-Device
.	O
</s>
<s>
The	O
enclosure	O
also	O
plays	O
a	O
role	O
in	O
managing	O
vibration	O
induced	O
by	O
the	O
driver	B-Algorithm
frame	O
and	O
moving	O
airmass	O
within	O
the	O
enclosure	O
,	O
as	O
well	O
as	O
heat	O
generated	O
by	O
driver	B-Algorithm
voice	O
coils	O
and	O
amplifiers	O
(	O
especially	O
where	O
woofers	B-Device
and	O
subwoofers	B-Application
are	O
concerned	O
)	O
.	O
</s>
<s>
Speaker	B-Device
enclosures	I-Device
designed	O
for	O
use	O
in	O
a	O
home	O
or	O
recording	O
studio	O
typically	O
do	O
not	O
have	O
handles	O
or	O
corner	O
protectors	O
,	O
although	O
they	O
do	O
still	O
usually	O
have	O
a	O
cloth	O
or	O
mesh	O
cover	O
to	O
protect	O
the	O
woofer	B-Device
and	O
tweeter	B-Device
.	O
</s>
<s>
These	O
speaker	B-Device
grilles	I-Device
are	O
a	O
metallic	O
or	O
cloth	O
mesh	O
that	O
are	O
used	O
to	O
protect	O
the	O
speaker	O
by	O
forming	O
a	O
protective	O
cover	O
over	O
the	O
speaker	O
's	O
cone	O
while	O
allowing	O
sound	O
to	O
pass	O
through	O
undistorted	O
.	O
</s>
<s>
Speaker	B-Device
enclosures	I-Device
are	O
used	O
in	O
homes	O
in	O
stereo	O
systems	O
,	O
home	O
cinema	O
systems	O
,	O
televisions	O
,	O
boom	O
boxes	O
and	O
many	O
other	O
audio	O
appliances	O
.	O
</s>
<s>
Small	O
speaker	B-Device
enclosures	I-Device
are	O
used	O
in	O
car	O
stereo	O
systems	O
.	O
</s>
<s>
Speaker	B-Device
cabinets	I-Device
are	O
key	O
components	O
of	O
a	O
number	O
of	O
commercial	O
applications	O
,	O
including	O
sound	O
reinforcement	O
systems	O
,	O
movie	O
theatre	O
sound	O
systems	O
and	O
recording	O
studios	O
.	O
</s>
<s>
Electric	O
musical	O
instruments	O
invented	O
in	O
the	O
20th	O
century	O
,	O
such	O
as	O
the	O
electric	O
guitar	O
,	O
electric	O
bass	O
and	O
synthesizer	O
,	O
among	O
others	O
,	O
are	O
amplified	O
using	O
instrument	O
amplifiers	O
and	O
speaker	B-Device
cabinets	I-Device
(	O
e.g.	O
,	O
guitar	O
amplifier	O
speaker	B-Device
cabinets	I-Device
)	O
.	O
</s>
<s>
Early	O
on	O
,	O
radio	O
loudspeakers	O
consisted	O
of	O
horns	B-Device
,	O
often	O
sold	O
separately	O
from	O
the	O
radio	O
itself	O
(	O
typically	O
a	O
small	O
wood	O
box	O
containing	O
the	O
radio	O
's	O
electronic	O
circuits	O
)	O
,	O
so	O
they	O
were	O
not	O
usually	O
housed	O
in	O
an	O
enclosure	O
.	O
</s>
<s>
When	O
paper	O
cone	O
loudspeaker	B-Device
drivers	I-Device
were	O
introduced	O
in	O
the	O
mid	O
1920s	O
,	O
radio	O
cabinets	O
began	O
to	O
be	O
made	O
larger	O
to	O
enclose	O
both	O
the	O
electronics	O
and	O
the	O
loudspeaker	O
.	O
</s>
<s>
Before	O
the	O
1950s	O
many	O
manufacturers	O
did	O
not	O
fully	O
enclose	O
their	O
loudspeaker	B-Device
cabinets	I-Device
;	O
the	O
back	O
of	O
the	O
cabinet	O
was	O
typically	O
left	O
open	O
.	O
</s>
<s>
Most	O
of	O
the	O
enclosure	O
types	O
discussed	O
in	O
this	O
article	O
were	O
invented	O
either	O
to	O
wall	O
off	O
the	O
out	O
of	O
phase	O
sound	O
from	O
one	O
side	O
of	O
the	O
driver	B-Algorithm
,	O
or	O
to	O
modify	O
it	O
so	O
that	O
it	O
could	O
be	O
used	O
to	O
enhance	O
the	O
sound	O
produced	O
from	O
the	O
other	O
side	O
.	O
</s>
<s>
In	O
some	O
respects	O
,	O
the	O
ideal	O
mounting	O
for	O
a	O
low-frequency	O
loudspeaker	B-Device
driver	I-Device
would	O
be	O
a	O
rigid	O
flat	O
panel	O
of	O
infinite	O
size	O
with	O
infinite	O
space	O
behind	O
it	O
.	O
</s>
<s>
This	O
would	O
entirely	O
prevent	O
the	O
rear	O
sound	O
waves	O
from	O
interfering	O
(	O
i.e.	O
,	O
comb	B-Algorithm
filter	I-Algorithm
cancellations	O
)	O
with	O
the	O
sound	O
waves	O
from	O
the	O
front	O
.	O
</s>
<s>
An	O
"	O
open	O
baffle	O
"	O
loudspeaker	O
is	O
an	O
approximation	O
of	O
this	O
,	O
since	O
the	O
driver	B-Algorithm
is	O
mounted	O
on	O
a	O
panel	O
,	O
with	O
dimensions	O
comparable	O
to	O
the	O
longest	O
wavelength	O
to	O
be	O
reproduced	O
.	O
</s>
<s>
In	O
either	O
case	O
,	O
the	O
driver	B-Algorithm
would	O
need	O
a	O
relatively	O
stiff	O
suspension	O
to	O
provide	O
the	O
restoring	O
force	O
which	O
might	O
have	O
been	O
provided	O
at	O
low	O
frequencies	O
by	O
a	O
smaller	O
sealed	O
or	O
ported	O
enclosure	O
,	O
so	O
few	O
drivers	O
are	O
suitable	O
for	O
this	O
kind	O
of	O
mounting	O
.	O
</s>
<s>
The	O
forward	O
-	O
and	O
rearward-generated	O
sounds	O
of	O
a	O
speaker	B-Device
driver	I-Device
appear	O
out	O
of	O
phase	O
from	O
each	O
other	O
because	O
they	O
are	O
generated	O
through	O
the	O
opposite	O
motion	O
of	O
the	O
diaphragm	B-Device
and	O
because	O
they	O
travel	O
different	O
paths	O
before	O
converging	O
at	O
the	O
listener	O
's	O
position	O
.	O
</s>
<s>
A	O
speaker	B-Device
driver	I-Device
mounted	O
on	O
a	O
finite	O
baffle	O
will	O
display	O
a	O
physical	O
phenomenon	O
known	O
as	O
interference	O
which	O
can	O
result	O
in	O
perceivable	O
frequency-dependent	O
sound	O
attenuation	O
.	O
</s>
<s>
at	O
lower	O
frequencies	O
)	O
,	O
most	O
loudspeaker	B-Device
cabinets	I-Device
use	O
some	O
sort	O
of	O
structure	O
(	O
usually	O
a	O
box	O
)	O
to	O
contain	O
the	O
out	O
of	O
phase	O
sound	O
energy	O
.	O
</s>
<s>
Enclosures	O
can	O
have	O
a	O
significant	O
effect	O
beyond	O
what	O
was	O
intended	O
,	O
with	O
panel	O
resonances	B-Application
,	O
diffraction	O
from	O
cabinet	O
edges	O
and	O
standing	O
wave	O
energy	O
from	O
internal	O
reflection/reinforcement	O
modes	O
being	O
among	O
the	O
possible	O
problems	O
.	O
</s>
<s>
Bothersome	O
resonances	B-Application
can	O
be	O
reduced	O
by	O
increasing	O
enclosure	O
mass	O
or	O
rigidity	O
,	O
by	O
increasing	O
the	O
damping	O
of	O
enclosure	O
walls	O
or	O
wall/surface	O
treatment	O
combinations	O
,	O
by	O
adding	O
stiff	O
cross	O
bracing	O
,	O
or	O
by	O
adding	O
internal	O
absorption	O
.	O
</s>
<s>
Wharfedale	O
,	O
in	O
some	O
designs	O
,	O
reduced	O
panel	O
resonance	B-Application
by	O
using	O
two	O
wooden	O
cabinets	O
(	O
one	O
inside	O
the	O
other	O
)	O
with	O
the	O
space	O
between	O
filled	O
with	O
sand	O
.	O
</s>
<s>
Sometimes	O
the	O
differences	O
in	O
phase	O
response	O
at	O
frequencies	O
shared	O
by	O
different	O
drivers	O
can	O
be	O
addressed	O
by	O
adjusting	O
the	O
vertical	O
location	O
of	O
the	O
smaller	O
drivers	O
(	O
usually	O
backwards	O
)	O
,	O
or	O
by	O
leaning	O
or	O
'	O
stepping	O
 '	O
the	O
front	O
baffle	O
,	O
so	O
that	O
the	O
wavefront	O
from	O
all	O
drivers	O
is	O
coherent	O
at	O
and	O
around	O
the	O
crossover	B-Algorithm
frequencies	I-Algorithm
in	O
the	O
speaker	O
's	O
normal	O
sound	O
field	O
.	O
</s>
<s>
The	O
acoustic	O
center	O
of	O
the	O
driver	B-Algorithm
dictates	O
the	O
amount	O
of	O
rearward	O
offset	O
needed	O
to	O
"	O
time-align	O
"	O
the	O
drivers	O
.	O
</s>
<s>
Enclosures	O
used	O
for	O
woofers	B-Device
and	O
subwoofers	B-Application
can	O
be	O
adequately	O
modeled	O
in	O
the	O
low-frequency	O
region	O
(	O
approximately	O
100	O
–	O
200Hz	O
and	O
below	O
)	O
using	O
acoustics	O
and	O
the	O
lumped	O
component	O
models	O
.	O
</s>
<s>
The	O
designer	O
must	O
balance	O
low	O
bass	O
extension	O
,	O
linear	O
frequency	O
response	O
,	O
efficiency	O
,	O
distortion	O
,	O
loudness	O
and	O
enclosure	O
size	O
,	O
while	O
simultaneously	O
addressing	O
issues	O
higher	O
in	O
the	O
audible	O
frequency	O
range	O
such	O
as	O
diffraction	O
from	O
enclosure	O
edges	O
,	O
the	O
baffle	O
step	O
effect	O
when	O
wavelengths	O
approach	O
enclosure	O
dimensions	O
,	O
crossovers	B-Algorithm
,	O
and	O
driver	B-Algorithm
blending	O
.	O
</s>
<s>
The	O
loudspeaker	B-Device
driver	I-Device
's	O
moving	O
mass	O
and	O
compliance	B-Algorithm
(	O
slackness	O
or	O
reciprocal	O
stiffness	B-Algorithm
of	O
the	O
suspension	O
)	O
determines	O
the	O
driver	B-Algorithm
's	O
resonance	B-Application
frequency	O
(	O
Fs	O
)	O
.	O
</s>
<s>
Output	O
falls	O
below	O
the	O
system	O
's	O
resonance	B-Application
frequency	O
(	O
Fc	O
)	O
,	O
defined	O
as	O
the	O
frequency	O
of	O
peak	O
impedance	O
.	O
</s>
<s>
The	O
enclosure	O
or	O
driver	B-Algorithm
must	O
have	O
a	O
small	O
leak	O
so	O
that	O
the	O
internal	O
and	O
external	O
pressures	O
can	O
equalise	O
over	O
time	O
,	O
to	O
compensate	O
for	O
changes	O
in	O
barometric	O
pressure	O
or	O
altitude	O
;	O
the	O
porous	O
nature	O
of	O
paper	O
cones	O
,	O
or	O
an	O
imperfectly	O
sealed	O
enclosure	O
,	O
is	O
normally	O
sufficient	O
to	O
provide	O
this	O
slow	O
pressure	O
equalisation	O
.	O
</s>
<s>
A	O
variation	O
on	O
the	O
'	O
open	O
baffle	O
 '	O
approach	O
is	O
to	O
mount	O
the	O
loudspeaker	B-Device
driver	I-Device
in	O
a	O
very	O
large	O
sealed	O
enclosure	O
,	O
providing	O
minimal	O
'	O
air	O
spring	O
 '	O
restoring	O
force	O
to	O
the	O
cone	O
.	O
</s>
<s>
This	O
minimizes	O
the	O
change	O
in	O
the	O
driver	B-Algorithm
's	O
resonance	B-Application
frequency	O
caused	O
by	O
the	O
enclosure	O
.	O
</s>
<s>
This	O
is	O
often	O
the	O
case	O
with	O
exotic	O
rotary	B-Device
woofer	I-Device
installations	O
,	O
as	O
they	O
are	O
intended	O
to	O
go	O
to	O
frequencies	O
lower	O
than	O
20Hz	O
and	O
displace	O
large	O
volumes	O
of	O
air	O
.	O
</s>
<s>
"	O
Infinite	O
baffle	O
"	O
or	O
simply	O
"	O
IB	O
"	O
is	O
also	O
used	O
as	O
a	O
generic	O
term	O
for	O
sealed	O
enclosures	O
of	O
any	O
size	O
,	O
the	O
name	O
being	O
used	O
because	O
of	O
the	O
ability	O
of	O
a	O
sealed	O
enclosure	O
to	O
prevent	O
any	O
interaction	O
between	O
the	O
forward	O
and	O
rear	O
radiation	O
of	O
a	O
driver	B-Algorithm
at	O
low	O
frequencies	O
.	O
</s>
<s>
The	O
term	O
is	O
often	O
and	O
erroneously	O
used	O
of	O
sealed	O
enclosures	O
which	O
cannot	O
exhibit	O
infinite-baffle	O
behavior	O
unless	O
their	O
internal	O
volume	O
is	O
much	O
greater	O
than	O
the	O
Vas	O
Thiele/Small	B-Device
of	O
the	O
drive	O
unit	O
AND	O
the	O
front	O
baffle	O
dimensions	O
are	O
ideally	O
several	O
wavelengths	O
of	O
the	O
lowest	O
output	O
frequency	O
.	O
</s>
<s>
Acoustic	B-Architecture
suspension	I-Architecture
or	O
air	O
suspension	O
is	O
a	O
variation	O
of	O
the	O
closed-box	O
enclosure	O
,	O
using	O
a	O
box	O
size	O
that	O
exploits	O
the	O
almost	O
linear	O
air	O
spring	O
resulting	O
in	O
a	O
−3dB	O
low-frequency	O
cut-off	O
point	O
of	O
30	O
–	O
40Hz	O
from	O
a	O
box	O
of	O
only	O
one	O
to	O
two	O
cubic	O
feet	O
or	O
so	O
.	O
</s>
<s>
The	O
"	O
spring	O
"	O
suspension	O
that	O
restores	O
the	O
cone	O
to	O
a	O
neutral	O
position	O
is	O
a	O
combination	O
of	O
an	O
exceptionally	O
compliant	O
(	O
soft	O
)	O
woofer	B-Device
suspension	O
,	O
and	O
the	O
air	O
inside	O
the	O
enclosure	O
.	O
</s>
<s>
At	O
frequencies	O
below	O
system	O
resonance	B-Application
,	O
the	O
air	O
pressure	O
caused	O
by	O
the	O
cone	O
motion	O
is	O
the	O
dominant	O
force	O
.	O
</s>
<s>
The	O
acoustic	B-Architecture
suspension	I-Architecture
principle	O
takes	O
advantage	O
of	O
this	O
relatively	O
linear	O
spring	O
.	O
</s>
<s>
For	O
a	O
specific	O
driver	B-Algorithm
,	O
an	O
optimal	O
acoustic	B-Architecture
suspension	I-Architecture
cabinet	O
will	O
be	O
smaller	O
than	O
a	O
bass	O
reflex	O
,	O
but	O
the	O
bass	O
reflex	O
cabinet	O
will	O
have	O
a	O
lower	O
−3dB	O
point	O
.	O
</s>
<s>
The	O
voltage	O
sensitivity	O
above	O
the	O
tuning	O
frequency	O
remains	O
a	O
function	O
of	O
the	O
driver	B-Algorithm
,	O
and	O
not	O
of	O
the	O
cabinet	O
design	O
.	O
</s>
<s>
The	O
isobaric	O
loudspeaker	O
configuration	O
was	O
first	O
introduced	O
by	O
Harry	O
F	O
.	O
Olson	O
in	O
the	O
early	O
1950s	O
,	O
and	O
refers	O
to	O
systems	O
in	O
which	O
two	O
or	O
more	O
identical	O
woofers	B-Device
(	O
bass	O
drivers	O
)	O
operate	O
simultaneously	O
,	O
with	O
a	O
common	O
body	O
of	O
enclosed	O
air	O
adjoining	O
one	O
side	O
of	O
each	O
diaphragm	B-Device
.	O
</s>
<s>
Bass	O
reflex	O
designs	O
are	O
used	O
in	O
home	O
stereo	O
speakers	O
(	O
including	O
both	O
low	O
-	O
to	O
mid-priced	O
speaker	B-Device
cabinets	I-Device
and	O
expensive	O
hi-fi	O
cabinets	O
)	O
,	O
bass	O
amplifier	O
speaker	B-Device
cabinets	I-Device
,	O
keyboard	O
amplifier	O
cabinets	O
,	O
subwoofer	B-Application
cabinets	O
and	O
PA	O
system	O
speaker	B-Device
cabinets	I-Device
.	O
</s>
<s>
They	O
deliberately	O
and	O
successfully	O
exploit	O
Helmholtz	O
resonance	B-Application
.	O
</s>
<s>
In	O
particular	O
Thiele	B-Device
and	I-Device
Small	I-Device
became	O
very	O
well	O
known	O
for	O
their	O
work	O
.	O
</s>
<s>
While	O
ported	O
loudspeakers	O
had	O
been	O
produced	O
for	O
many	O
years	O
before	O
computer	O
modeling	O
,	O
achieving	O
optimum	O
performance	O
was	O
challenging	O
,	O
as	O
it	O
is	O
a	O
complex	O
sum	O
of	O
the	O
properties	O
of	O
the	O
specific	O
driver	B-Algorithm
,	O
the	O
enclosure	O
and	O
port	O
,	O
because	O
of	O
imperfect	O
understanding	O
of	O
the	O
assorted	O
interactions	O
.	O
</s>
<s>
These	O
enclosures	O
are	O
sensitive	O
to	O
small	O
variations	O
in	O
driver	B-Algorithm
characteristics	O
and	O
require	O
special	O
quality	O
control	O
concern	O
for	O
uniform	O
performance	O
across	O
a	O
production	O
run	O
.	O
</s>
<s>
Bass	O
ports	O
are	O
widely	O
used	O
in	O
subwoofers	B-Application
for	O
PA	O
systems	O
and	O
sound	O
reinforcement	O
systems	O
,	O
in	O
bass	O
amp	O
speaker	B-Device
cabinets	I-Device
and	O
in	O
keyboard	O
amp	O
speaker	B-Device
cabinets	I-Device
.	O
</s>
<s>
A	O
passive	B-Architecture
radiator	I-Architecture
speaker	I-Architecture
uses	O
a	O
second	O
"	O
passive	O
"	O
driver	B-Algorithm
,	O
or	O
drone	O
,	O
to	O
produce	O
similar	O
low-frequency	O
extension	O
,	O
or	O
efficiency	O
increase	O
,	O
or	O
enclosure	O
size	O
reduction	O
,	O
similar	O
to	O
ported	O
enclosures	O
.	O
</s>
<s>
The	O
passive	O
driver	B-Algorithm
is	O
not	O
wired	O
to	O
an	O
amplifier	O
;	O
instead	O
,	O
it	O
moves	O
in	O
response	O
to	O
changing	O
enclosure	O
pressures	O
.	O
</s>
<s>
Tuning	O
adjustments	O
for	O
a	O
passive	B-Architecture
radiator	I-Architecture
are	O
usually	O
accomplished	O
more	O
quickly	O
than	O
with	O
a	O
bass	O
reflex	O
design	O
since	O
such	O
corrections	O
can	O
be	O
as	O
simple	O
as	O
mass	O
adjustments	O
to	O
the	O
drone	O
.	O
</s>
<s>
The	O
disadvantages	O
are	O
that	O
a	O
passive	B-Architecture
radiator	I-Architecture
requires	O
precision	O
construction	O
like	O
a	O
driver	B-Algorithm
,	O
thus	O
increasing	O
costs	O
,	O
and	O
may	O
have	O
excursion	O
limitations	O
.	O
</s>
<s>
A	O
4th-order	O
electrical	O
bandpass	O
filter	O
can	O
be	O
simulated	O
by	O
a	O
vented	O
box	O
in	O
which	O
the	O
contribution	O
from	O
the	O
rear	O
face	O
of	O
the	O
driver	B-Algorithm
cone	O
is	O
trapped	O
in	O
a	O
sealed	O
box	O
,	O
and	O
the	O
radiation	O
from	O
the	O
front	O
surface	O
of	O
the	O
cone	O
is	O
directed	O
into	O
a	O
ported	O
chamber	O
.	O
</s>
<s>
This	O
modifies	O
the	O
resonance	B-Application
of	O
the	O
driver	B-Algorithm
.	O
</s>
<s>
The	O
dividing	O
wall	O
between	O
the	O
chambers	O
holds	O
the	O
driver	B-Algorithm
;	O
typically	O
only	O
one	O
chamber	O
is	O
ported	O
.	O
</s>
<s>
If	O
the	O
enclosure	O
on	O
each	O
side	O
of	O
the	O
woofer	B-Device
has	O
a	O
port	O
in	O
it	O
then	O
the	O
enclosure	O
yields	O
a	O
6th-order	O
band-pass	O
response	O
.	O
</s>
<s>
These	O
are	O
considerably	O
harder	O
to	O
design	O
and	O
tend	O
to	O
be	O
very	O
sensitive	O
to	O
driver	B-Algorithm
characteristics	O
.	O
</s>
<s>
As	O
in	O
other	O
reflex	O
enclosures	O
,	O
the	O
ports	O
may	O
generally	O
be	O
replaced	O
by	O
passive	B-Architecture
radiators	I-Architecture
if	O
desired	O
.	O
</s>
<s>
This	O
design	O
falls	O
between	O
acoustic	B-Architecture
suspension	I-Architecture
and	O
bass	O
reflex	O
enclosures	O
.	O
</s>
<s>
The	O
result	O
is	O
control	O
of	O
the	O
resonance	B-Application
behavior	O
of	O
the	O
system	O
which	O
improves	O
low-frequency	O
reproduction	O
,	O
according	O
to	O
some	O
designers	O
.	O
</s>
<s>
Dynaco	O
was	O
a	O
primary	O
producer	O
of	O
these	O
enclosures	O
for	O
many	O
years	O
,	O
using	O
designs	O
developed	O
by	O
a	O
Scandinavian	O
driver	B-Algorithm
maker	O
.	O
</s>
<s>
A	O
reason	O
for	O
this	O
may	O
be	O
that	O
adding	O
damping	O
material	O
is	O
a	O
needlessly	O
inefficient	O
method	O
of	O
increasing	O
damping	O
;	O
the	O
same	O
alignment	O
can	O
be	O
achieved	O
by	O
simply	O
choosing	O
a	O
loudspeaker	B-Device
driver	I-Device
with	O
the	O
appropriate	O
parameters	B-Device
and	O
precisely	O
tuning	O
the	O
enclosure	O
and	O
port	O
for	O
the	O
desired	O
response	O
.	O
</s>
<s>
A	O
resistive	O
mat	O
is	O
placed	O
in	O
front	O
of	O
or	O
directly	O
behind	O
the	O
loudspeaker	B-Device
driver	I-Device
(	O
usually	O
mounted	O
on	O
the	O
rear	O
deck	O
of	O
the	O
car	O
in	O
order	O
to	O
use	O
the	O
trunk	O
as	O
an	O
enclosure	O
)	O
.	O
</s>
<s>
The	O
loudspeaker	B-Device
driver	I-Device
is	O
sealed	O
to	O
the	O
mat	O
so	O
that	O
all	O
acoustic	O
output	O
in	O
one	O
direction	O
must	O
pass	O
through	O
the	O
mat	O
.	O
</s>
<s>
This	O
increases	O
mechanical	O
damping	O
,	O
and	O
the	O
resulting	O
decrease	O
in	O
the	O
impedance	O
magnitude	O
at	O
resonance	B-Application
is	O
generally	O
the	O
desired	O
effect	O
,	O
though	O
there	O
is	O
no	O
perceived	O
or	O
objective	O
benefit	O
to	O
this	O
.	O
</s>
<s>
Again	O
,	O
this	O
technique	O
reduces	O
efficiency	O
and	O
the	O
same	O
result	O
can	O
be	O
achieved	O
through	O
selection	O
of	O
a	O
driver	B-Algorithm
with	O
a	O
lower	O
Q	O
factor	O
,	O
or	O
even	O
via	O
electronic	O
equalization	O
.	O
</s>
<s>
A	O
dipole	O
enclosure	O
in	O
its	O
simplest	O
form	O
is	O
a	O
driver	B-Algorithm
located	O
on	O
a	O
flat	O
baffle	O
panel	O
,	O
similar	O
to	O
older	O
open	O
back	O
cabinet	O
designs	O
.	O
</s>
<s>
A	O
horn	B-Device
loudspeaker	I-Device
is	O
a	O
speaker	O
system	O
using	O
a	O
horn	O
to	O
match	O
the	O
driver	B-Algorithm
cone	O
to	O
the	O
air	O
.	O
</s>
<s>
The	O
horn	O
structure	O
itself	O
does	O
not	O
amplify	O
,	O
but	O
rather	O
improves	O
the	O
coupling	O
between	O
the	O
speaker	B-Device
driver	I-Device
and	O
the	O
air	O
.	O
</s>
<s>
Properly	O
designed	O
horns	B-Device
have	O
the	O
effect	O
of	O
making	O
the	O
speaker	B-Device
cone	I-Device
transfer	O
more	O
of	O
the	O
electrical	O
energy	O
in	O
the	O
voice	O
coil	O
into	O
the	O
air	O
;	O
in	O
effect	O
the	O
driver	B-Algorithm
appears	O
to	O
have	O
higher	O
efficiency	O
.	O
</s>
<s>
Horns	B-Device
can	O
help	O
control	O
dispersion	O
at	O
higher	O
frequencies	O
which	O
is	O
useful	O
in	O
some	O
applications	O
such	O
as	O
sound	O
reinforcement	O
.	O
</s>
<s>
Properly	O
designed	O
horns	B-Device
for	O
high	O
frequencies	O
are	O
small	O
(	O
above	O
say	O
3kHz	O
or	O
so	O
,	O
a	O
few	O
centimetres	O
or	O
inches	O
)	O
,	O
those	O
for	O
mid-range	O
frequencies	O
(	O
perhaps	O
300Hz	O
to	O
2kHz	O
)	O
much	O
larger	O
,	O
perhaps	O
30	O
to	O
60cm	O
(	O
1	O
or	O
2	O
feet	O
)	O
,	O
and	O
for	O
low	O
frequencies	O
(	O
under	O
300Hz	O
)	O
very	O
large	O
,	O
a	O
few	O
metres	O
(	O
dozens	O
of	O
feet	O
)	O
.	O
</s>
<s>
In	O
the	O
1950s	O
,	O
a	O
few	O
high	O
fidelity	O
enthusiasts	O
actually	O
built	O
full	O
sized	O
horns	B-Device
whose	O
structures	O
were	O
built	O
into	O
a	O
house	O
wall	O
or	O
basement	O
.	O
</s>
<s>
With	O
the	O
coming	O
of	O
stereo	O
(	O
two	O
speakers	O
)	O
and	O
surround	O
sound	O
(	O
four	O
or	O
more	O
)	O
,	O
plain	O
horns	B-Device
became	O
even	O
more	O
impractical	O
.	O
</s>
<s>
Various	O
speaker	O
manufacturers	O
have	O
produced	O
folded	O
low-frequency	O
horns	B-Device
which	O
are	O
much	O
smaller	O
(	O
e.g.	O
,	O
Altec	O
Lansing	O
,	O
JBL	O
,	O
Klipsch	O
,	O
Lowther	O
,	O
Tannoy	O
)	O
and	O
actually	O
fit	O
in	O
practical	O
rooms	O
.	O
</s>
<s>
The	O
multiple	O
entry	O
horn	O
(	O
also	O
known	O
as	O
a	O
coentrant	O
horn	O
,	O
unity	O
horn	O
or	O
synergy	O
horn	O
)	O
is	O
a	O
manifold	O
speaker	O
design	O
;	O
it	O
uses	O
several	O
different	O
drivers	O
mounted	O
on	O
the	O
horn	O
at	O
stepped	O
distances	O
from	O
the	O
horn	O
's	O
apex	O
,	O
where	O
the	O
high	O
frequency	O
driver	B-Algorithm
is	O
placed	O
.	O
</s>
<s>
Both	O
sides	O
of	O
a	O
long-excursion	O
high-power	O
driver	B-Algorithm
in	O
a	O
tapped	O
horn	O
enclosure	O
are	O
ported	O
into	O
the	O
horn	O
itself	O
,	O
with	O
one	O
path	O
length	O
long	O
and	O
the	O
other	O
short	O
.	O
</s>
<s>
This	O
design	O
is	O
especially	O
effective	O
at	O
subwoofer	B-Application
frequencies	O
and	O
offers	O
reductions	O
in	O
enclosure	O
size	O
along	O
with	O
more	O
output	O
.	O
</s>
<s>
A	O
perfect	O
transmission	B-Architecture
line	I-Architecture
loudspeaker	I-Architecture
enclosure	O
has	O
an	O
infinitely	O
long	O
line	O
,	O
stuffed	O
with	O
absorbent	O
material	O
such	O
that	O
all	O
the	O
rear	O
radiation	O
of	O
the	O
driver	B-Algorithm
is	O
fully	O
absorbed	O
,	O
down	O
to	O
the	O
lowest	O
frequencies	O
.	O
</s>
<s>
Stuffing	O
often	O
is	O
of	O
different	O
materials	O
and	O
densities	O
,	O
changing	O
as	O
one	O
gets	O
further	O
from	O
the	O
back	O
of	O
the	O
driver	B-Algorithm
's	O
diaphragm	B-Device
.	O
</s>
<s>
Consequent	O
to	O
the	O
above	O
,	O
practical	O
transmission	B-Architecture
line	I-Architecture
loudspeakers	I-Architecture
are	O
not	O
true	O
transmission	O
lines	O
,	O
as	O
there	O
is	O
generally	O
output	O
from	O
the	O
vent	O
at	O
the	O
lowest	O
frequencies	O
.	O
</s>
<s>
They	O
can	O
be	O
thought	O
of	O
as	O
a	O
waveguide	O
in	O
which	O
the	O
structure	O
shifts	O
the	O
phase	O
of	O
the	O
driver	B-Algorithm
's	O
rear	O
output	O
by	O
at	O
least	O
90°	O
,	O
thereby	O
reinforcing	O
the	O
frequencies	O
near	O
the	O
driver	B-Algorithm
's	O
free-air	O
resonance	B-Application
frequency	O
Fs	O
.	O
</s>
<s>
But	O
it	O
is	O
the	O
inherent	O
resonance	B-Application
(	O
typically	O
at	O
1/4	O
wavelength	O
)	O
that	O
can	O
enhance	O
the	O
bass	O
response	O
in	O
this	O
type	O
of	O
enclosure	O
,	O
albeit	O
with	O
less	O
absorbent	O
stuffing	O
.	O
</s>
<s>
The	O
tapering	O
tube	O
can	O
be	O
coiled	O
for	O
lower	O
frequency	O
driver	B-Algorithm
enclosures	O
to	O
reduce	O
the	O
dimensions	O
of	O
the	O
speaker	O
system	O
,	O
resulting	O
in	O
a	O
seashell	O
like	O
appearance	O
.	O
</s>
<s>
A	O
quarter	O
wave	O
resonator	O
is	O
a	O
transmission	O
line	O
tuned	O
to	O
form	O
a	O
standing	O
quarter	O
wave	O
at	O
a	O
frequency	O
somewhat	O
below	O
the	O
driver	B-Algorithm
's	O
resonance	B-Application
frequency	O
Fs	O
.	O
</s>
<s>
When	O
properly	O
designed	O
,	O
a	O
port	O
that	O
is	O
of	O
much	O
smaller	O
diameter	O
than	O
the	O
main	O
pipe	O
located	O
at	O
the	O
end	O
of	O
the	O
pipe	O
then	O
produces	O
the	O
driver	B-Algorithm
's	O
backward	O
radiation	O
in	O
phase	O
with	O
the	O
speaker	B-Device
driver	I-Device
itself	O
;	O
greatly	O
adding	O
to	O
the	O
bass	O
output	O
.	O
</s>
<s>
Quarter	O
wave	O
resonators	O
have	O
seen	O
a	O
revival	O
as	O
commercial	O
applications	O
with	O
the	O
onset	O
of	O
neodymium	O
drivers	O
that	O
enable	O
this	O
design	O
to	O
produce	O
relatively	O
low	O
bass	O
extensions	O
within	O
a	O
relatively	O
small	O
speaker	B-Device
enclosure	I-Device
.	O
</s>
<s>
The	O
concept	O
is	O
that	O
the	O
sound	O
emitted	O
from	O
the	O
rear	O
of	O
the	O
loudspeaker	B-Device
driver	I-Device
is	O
progressively	O
reflected	O
and	O
absorbed	O
along	O
the	O
length	O
of	O
the	O
tapering	O
tube	O
,	O
almost	O
completely	O
preventing	O
internally	O
reflected	O
sound	O
being	O
retransmitted	O
through	O
the	O
cone	O
of	O
the	O
loudspeaker	O
.	O
</s>
<s>
The	O
TQWP	O
is	O
also	O
known	O
as	O
a	O
Voigt	B-Architecture
pipe	I-Architecture
and	O
was	O
introduced	O
in	O
1934	O
by	O
Paul	O
G	O
.	O
A	O
.	O
H	O
.	O
Voigt	O
,	O
Lowther	O
's	O
original	O
driver	B-Algorithm
designer	O
.	O
</s>
