<s>
A	O
woofer	B-Device
or	O
bass	O
speaker	O
is	O
a	O
technical	O
term	O
for	O
a	O
loudspeaker	B-Device
driver	I-Device
designed	O
to	O
produce	O
low	O
frequency	O
sounds	O
,	O
typically	O
from	O
50	O
Hz	O
up	O
to	O
1000Hz	O
.	O
</s>
<s>
The	O
name	O
is	O
from	O
the	O
onomatopoeic	O
English	O
word	O
for	O
a	O
dog	O
's	O
bark	O
,	O
"	O
woof	O
"	O
(	O
in	O
contrast	O
to	O
the	O
name	O
used	O
for	O
loudspeakers	O
designed	O
to	O
reproduce	O
high-frequency	O
sounds	O
,	O
tweeter	B-Device
)	O
.	O
</s>
<s>
The	O
most	O
common	O
design	O
for	O
a	O
woofer	B-Device
is	O
the	O
electrodynamic	O
driver	B-Device
,	O
which	O
typically	O
uses	O
a	O
stiff	O
paper	O
cone	O
,	O
driven	O
by	O
a	O
voice	B-Device
coil	I-Device
surrounded	O
by	O
a	O
magnetic	O
field	O
.	O
</s>
<s>
The	O
voice	B-Device
coil	I-Device
is	O
attached	O
by	O
adhesives	O
to	O
the	O
back	O
of	O
the	O
loudspeaker	O
cone	O
.	O
</s>
<s>
The	O
voice	B-Device
coil	I-Device
and	O
the	O
magnet	O
form	O
a	O
linear	O
electric	O
motor	O
.	O
</s>
<s>
When	O
current	O
flows	O
through	O
the	O
voice	B-Device
coil	I-Device
,	O
the	O
coil	O
moves	O
in	O
relation	O
to	O
the	O
frame	O
according	O
to	O
Fleming	O
's	O
left	O
hand	O
rule	O
for	O
motors	O
,	O
causing	O
the	O
coil	O
to	O
push	O
or	O
pull	O
on	O
the	O
driver	B-Device
cone	O
in	O
a	O
piston-like	O
way	O
.	O
</s>
<s>
Woofers	B-Device
are	O
generally	O
used	O
to	O
cover	O
the	O
lowest	O
octaves	O
of	O
a	O
loudspeaker	O
's	O
frequency	O
range	O
.	O
</s>
<s>
In	O
two-way	O
loudspeaker	O
systems	O
,	O
the	O
drivers	O
handling	O
the	O
lower	O
frequencies	O
are	O
also	O
obliged	O
to	O
cover	O
a	O
substantial	O
part	O
of	O
the	O
midrange	B-Device
,	O
often	O
as	O
high	O
as	O
2000	O
to	O
5000Hz	O
;	O
such	O
drivers	O
are	O
commonly	O
termed	O
mid	O
woofers	B-Device
.	O
</s>
<s>
Since	O
the	O
1990s	O
,	O
a	O
type	O
of	O
woofer	B-Device
(	O
termed	O
subwoofer	B-Application
)	O
,	O
which	O
is	O
designed	O
for	O
very	O
low	O
frequencies	O
only	O
,	O
has	O
come	O
to	O
be	O
commonly	O
used	O
in	O
home	O
theater	O
systems	O
and	O
PA	O
systems	O
to	O
augment	O
the	O
bass	O
response	O
;	O
they	O
usually	O
handle	O
the	O
very	O
lowest	O
two	O
or	O
three	O
octaves	O
(	O
i.e.	O
,	O
from	O
as	O
low	O
as	O
20	O
to	O
80	O
or	O
120Hz	O
)	O
.	O
</s>
<s>
Good	O
woofer	B-Device
design	O
requires	O
effectively	O
converting	O
a	O
low	O
frequency	O
amplifier	O
signal	O
to	O
mechanical	O
air	O
movement	O
with	O
high	O
fidelity	O
and	O
acceptable	O
efficiency	O
,	O
and	O
is	O
both	O
assisted	O
and	O
complicated	O
by	O
the	O
necessity	O
of	O
using	O
a	O
loudspeaker	B-Device
enclosure	I-Device
to	O
couple	O
the	O
cone	O
motion	O
to	O
the	O
air	O
.	O
</s>
<s>
If	O
done	O
well	O
,	O
many	O
of	O
the	O
other	O
problems	O
of	O
woofer	B-Device
design	O
(	O
for	O
instance	O
,	O
linear	O
excursion	O
requirements	O
)	O
are	O
reduced	O
.	O
</s>
<s>
In	O
most	O
cases	O
the	O
woofer	B-Device
and	O
its	O
enclosure	O
must	O
be	O
designed	O
to	O
work	O
together	O
.	O
</s>
<s>
The	O
size	O
of	O
the	O
enclosure	O
is	O
a	O
function	O
of	O
the	O
longest	O
wavelengths	O
(	O
lowest	O
frequencies	O
)	O
to	O
be	O
reproduced	O
,	O
and	O
the	O
woofer	B-Device
enclosure	O
is	O
much	O
larger	O
than	O
required	O
for	O
midrange	B-Device
and	O
high	B-Device
frequencies	I-Device
.	O
</s>
<s>
A	O
crossover	B-Algorithm
network	I-Algorithm
,	O
either	O
passive	O
or	O
active	O
,	O
filters	O
the	O
band	O
of	O
frequencies	O
to	O
be	O
handled	O
by	O
the	O
woofer	B-Device
and	O
other	O
speakers	O
.	O
</s>
<s>
Normally	O
the	O
crossover	B-Algorithm
and	O
speaker	O
system	O
,	O
including	O
the	O
woofer	B-Device
,	O
are	O
expected	O
to	O
convert	O
the	O
electrical	O
signal	O
supplied	O
by	O
the	O
amplifier	O
to	O
an	O
acoustic	O
signal	O
of	O
identical	O
waveform	O
without	O
other	O
interaction	O
between	O
the	O
amplifier	O
and	O
speakers	O
,	O
although	O
sometimes	O
the	O
amplifier	O
and	O
speakers	O
are	O
designed	O
together	O
with	O
the	O
speakers	O
supplying	O
distortion-correcting	O
negative	O
feedback	O
to	O
the	O
amplifier	O
.	O
</s>
<s>
There	O
are	O
many	O
challenges	O
in	O
woofer	B-Device
design	O
and	O
manufacture	O
.	O
</s>
<s>
Most	O
have	O
to	O
do	O
with	O
controlling	O
the	O
motion	O
of	O
the	O
cone	O
so	O
the	O
electrical	O
signal	O
to	O
the	O
woofer	B-Device
's	O
voice	B-Device
coil	I-Device
is	O
faithfully	O
reproduced	O
by	O
the	O
sound	O
waves	O
produced	O
by	O
the	O
cone	O
's	O
motion	O
.	O
</s>
<s>
Problems	O
include	O
damping	O
the	O
cone	O
cleanly	O
without	O
audible	O
distortion	O
so	O
that	O
it	O
does	O
not	O
continue	O
to	O
move	O
,	O
causing	O
ringing	B-Algorithm
,	O
when	O
the	O
instantaneous	O
input	O
signal	O
falls	O
to	O
zero	O
each	O
cycle	O
,	O
and	O
managing	O
high	O
excursions	O
(	O
usually	O
required	O
to	O
reproduce	O
loud	O
sounds	O
)	O
with	O
low	O
distortion	O
.	O
</s>
<s>
In	O
1965	O
,	O
Sennheiser	O
Electronics	O
introduced	O
the	O
Philharmonic	O
sound	O
system	O
,	O
which	O
used	O
electronics	O
to	O
overcome	O
some	O
of	O
the	O
problems	O
ordinary	O
woofer	B-Device
subsystems	O
confront	O
.	O
</s>
<s>
They	O
added	O
a	O
motion	O
sensor	O
to	O
the	O
woofer	B-Device
,	O
and	O
used	O
the	O
signal	O
corresponding	O
to	O
its	O
actual	O
motion	O
to	O
feedback	O
as	O
a	O
control	O
input	O
to	O
a	O
specially	O
designed	O
amplifier	O
.	O
</s>
<s>
As	O
electronics	O
costs	O
have	O
decreased	O
,	O
it	O
has	O
become	O
common	O
to	O
have	O
sensor-equipped	O
woofers	B-Device
in	O
inexpensive	O
'	O
music	O
systems	O
 '	O
,	O
boom	O
boxes	O
,	O
or	O
even	O
car	O
audio	O
systems	O
.	O
</s>
<s>
Computer	O
techniques	O
,	O
in	O
particular	O
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
(	O
DSP	O
)	O
,	O
make	O
possible	O
a	O
higher	O
precision	O
crossover	B-Algorithm
.	O
</s>
<s>
By	O
using	O
finite	O
impulse	O
response	O
(	O
FIR	O
)	O
and	O
other	O
digital	O
techniques	O
,	O
the	O
crossovers	B-Algorithm
for	O
a	O
bi-amped	O
or	O
tri-amped	O
system	O
can	O
be	O
accomplished	O
with	O
a	O
precision	O
not	O
possible	O
with	O
analog	O
filters	O
,	O
whether	O
passive	O
or	O
active	O
.	O
</s>
<s>
Furthermore	O
,	O
many	O
driver	B-Device
peculiarities	O
(	O
down	O
to	O
and	O
including	O
individual	O
variances	O
)	O
can	O
be	O
remedied	O
at	O
the	O
same	O
time	O
such	O
as	O
in	O
Klein	O
and	O
Hummel	O
's	O
recent	O
designs	O
.	O
</s>
<s>
The	O
three	O
chief	O
properties	O
designers	O
look	O
for	O
in	O
cones	O
are	O
light	O
weight	O
,	O
stiffness	O
,	O
and	O
lack	O
of	O
coloration	O
(	O
due	O
to	O
absence	O
of	O
ringing	B-Algorithm
)	O
.	O
</s>
<s>
Exotic	O
materials	O
like	O
Kevlar	O
and	O
magnesium	O
are	O
light	O
and	O
stiff	O
,	O
but	O
can	O
have	O
ringing	B-Algorithm
problems	O
,	O
depending	O
on	O
their	O
fabrication	O
and	O
design	O
.	O
</s>
<s>
Materials	O
like	O
paper	O
(	O
including	O
coated	O
paper	O
cones	O
)	O
and	O
various	O
polymers	B-Language
will	O
generally	O
ring	O
less	O
than	O
metal	O
diaphragms	O
,	O
but	O
can	O
be	O
heavier	O
and	O
not	O
as	O
stiff	O
.	O
</s>
<s>
There	O
have	O
been	O
good	O
and	O
bad	O
woofers	B-Device
made	O
with	O
every	O
type	O
of	O
cone	O
material	O
.	O
</s>
<s>
The	O
frame	O
,	O
or	O
basket	O
,	O
is	O
the	O
structure	O
holding	O
the	O
cone	O
,	O
voice	B-Device
coil	I-Device
and	O
magnet	O
in	O
the	O
proper	O
alignment	O
.	O
</s>
<s>
Since	O
the	O
voice	B-Device
coil	I-Device
gap	O
is	O
quite	O
narrow	O
(	O
clearances	O
are	O
typically	O
in	O
the	O
low	O
thousandths	O
of	O
an	O
inch	O
)	O
,	O
rigidity	O
is	O
important	O
to	O
prevent	O
rubbing	O
of	O
the	O
voice	B-Device
coil	I-Device
against	O
the	O
magnet	O
structure	O
in	O
the	O
gap	O
and	O
also	O
avoid	O
extraneous	O
motions	O
.	O
</s>
<s>
An	O
important	O
woofer	B-Device
specification	O
is	O
its	O
power	O
rating	O
,	O
the	O
amount	O
of	O
power	O
the	O
woofer	B-Device
can	O
handle	O
without	O
damage	O
.	O
</s>
<s>
Woofer	B-Device
power	O
ratings	O
become	O
important	O
when	O
the	O
speaker	O
is	O
pushed	O
to	O
extremes	O
:	O
applications	O
requiring	O
high	O
output	O
,	O
amplifier	O
overload	O
conditions	O
,	O
unusual	O
signals	O
(	O
i.e.	O
,	O
non-musical	O
ones	O
)	O
,	O
very	O
low	O
frequencies	O
at	O
which	O
the	O
enclosure	O
provides	O
little	O
or	O
no	O
acoustic	O
loading	O
(	O
and	O
so	O
there	O
will	O
be	O
maximum	O
cone	O
excursion	O
)	O
,	O
or	O
amplifier	O
failure	O
.	O
</s>
<s>
In	O
high-volume	O
situations	O
,	O
a	O
woofer	B-Device
's	O
voice	B-Device
coil	I-Device
will	O
heat	O
up	O
,	O
increase	O
its	O
resistance	O
,	O
causing	O
"	O
power	O
compression	O
"	O
,	O
a	O
condition	O
where	O
output	O
sound	O
power	O
level	O
decreases	O
after	O
extended	O
high	O
power	O
activity	O
.	O
</s>
<s>
Further	O
heating	O
can	O
physically	O
distort	O
the	O
voice	B-Device
coil	I-Device
,	O
causing	O
scuffing	O
,	O
shorting	O
due	O
to	O
wire	O
insulation	O
deterioration	O
,	O
or	O
other	O
electrical	O
or	O
mechanical	O
damage	O
.	O
</s>
<s>
Sudden	O
impulse	O
energy	O
can	O
melt	O
a	O
section	O
of	O
voice	B-Device
coil	I-Device
wire	O
,	O
causing	O
an	O
open	O
circuit	O
and	O
a	O
dead	O
woofer	B-Device
;	O
the	O
necessary	O
level	O
will	O
vary	O
with	O
driver	B-Device
characteristics	O
.	O
</s>
<s>
In	O
normal	O
listening	O
level	O
music	O
applications	O
,	O
the	O
electrical	O
power	O
rating	O
of	O
woofers	B-Device
is	O
generally	O
unimportant	O
;	O
it	O
remains	O
important	O
for	O
higher	O
frequency	O
drivers	O
.	O
</s>
<s>
There	O
are	O
three	O
types	O
of	O
power	O
handling	O
in	O
loudspeaker	B-Device
drivers	I-Device
,	O
including	O
woofers	B-Device
:	O
thermal	O
(	O
heat	O
)	O
,	O
electrical	O
(	O
both	O
covered	O
above	O
)	O
,	O
and	O
mechanical	O
.	O
</s>
<s>
Thermal	O
power	O
handling	O
limits	O
may	O
be	O
reached	O
when	O
fairly	O
high	O
power	O
levels	O
are	O
fed	O
to	O
a	O
woofer	B-Device
for	O
too	O
long	O
,	O
even	O
if	O
not	O
exceeding	O
mechanical	O
limits	O
at	O
any	O
time	O
.	O
</s>
<s>
Most	O
of	O
the	O
energy	O
applied	O
to	O
the	O
voice	B-Device
coil	I-Device
is	O
converted	O
to	O
heat	O
,	O
not	O
sound	O
;	O
all	O
of	O
the	O
heat	O
is	O
ultimately	O
passed	O
to	O
the	O
pole	O
piece	O
,	O
the	O
rest	O
of	O
the	O
magnet	O
structure	O
,	O
and	O
the	O
frame	O
.	O
</s>
<s>
From	O
the	O
woofer	B-Device
structure	O
,	O
the	O
heat	O
is	O
eventually	O
dissipated	O
into	O
the	O
surrounding	O
air	O
.	O
</s>
<s>
If	O
too	O
much	O
power	O
is	O
applied	O
to	O
the	O
voice	B-Device
coil	I-Device
as	O
compared	O
to	O
its	O
ability	O
to	O
shed	O
heat	O
,	O
it	O
will	O
eventually	O
exceed	O
a	O
maximum	O
safe	O
temperature	O
.	O
</s>
<s>
Adhesives	O
can	O
melt	O
,	O
the	O
voice	B-Device
coil	I-Device
former	O
can	O
melt	O
or	O
distort	O
,	O
or	O
the	O
insulation	O
separating	O
the	O
voice	B-Device
coil	I-Device
windings	O
can	O
fail	O
.	O
</s>
<s>
Each	O
of	O
these	O
events	O
will	O
damage	O
the	O
woofer	B-Device
,	O
perhaps	O
beyond	O
usability	O
.	O
</s>
<s>
Woofers	B-Device
designed	O
for	O
public	O
address	O
system	O
(	O
PA	O
)	O
and	O
instrument	O
amplifier	O
applications	O
are	O
similar	O
in	O
makeup	O
to	O
home	O
audio	O
woofers	B-Device
,	O
except	O
that	O
they	O
are	O
usually	O
designed	O
more	O
ruggedly	O
.	O
</s>
<s>
Typically	O
,	O
design	O
variances	O
include	O
:	O
cabinets	O
built	O
for	O
repeated	O
shipping	O
and	O
handling	O
,	O
larger	O
woofer	B-Device
cones	O
to	O
allow	O
for	O
higher	O
sound	O
pressure	O
levels	O
,	O
more	O
robust	O
voice	B-Device
coils	I-Device
to	O
withstand	O
higher	O
power	O
,	O
and	O
higher	O
suspension	O
stiffness	O
.	O
</s>
<s>
Generally	O
,	O
a	O
home	O
woofer	B-Device
used	O
in	O
a	O
PA/instrument	O
application	O
can	O
be	O
expected	O
to	O
fail	O
more	O
quickly	O
than	O
a	O
PA/instrument	O
woofer	B-Device
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
a	O
PA/instrument	O
woofer	B-Device
in	O
a	O
home	O
audio	O
application	O
will	O
not	O
have	O
the	O
same	O
quality	O
of	O
performance	O
,	O
particularly	O
at	O
low	O
volumes	O
.	O
</s>
<s>
A	O
PA	O
woofer	B-Device
will	O
not	O
produce	O
the	O
same	O
audible	O
high	O
fidelity	O
which	O
is	O
the	O
goal	O
of	O
high	O
quality	O
home	O
audio	O
due	O
to	O
those	O
differences	O
.	O
</s>
<s>
PA	O
system	O
woofers	B-Device
typically	O
have	O
high	O
efficiency	O
and	O
high	O
power	O
handling	O
capacity	O
.	O
</s>
<s>
The	O
trade-off	O
for	O
high	O
efficiency	O
at	O
reasonable	O
cost	O
is	O
usually	O
relatively	O
low	O
excursion	O
capability	O
(	O
i.e.	O
,	O
inability	O
to	O
move	O
"	O
in	O
and	O
out	O
"	O
as	O
far	O
as	O
many	O
home	O
woofers	B-Device
can	O
)	O
,	O
as	O
they	O
are	O
intended	O
for	O
horn	O
or	O
large	O
reflex	O
enclosures	O
.	O
</s>
<s>
A	O
home	O
stereo	O
woofer	B-Device
,	O
because	O
it	O
is	O
used	O
at	O
relatively	O
low	O
volumes	O
,	O
may	O
be	O
able	O
to	O
handle	O
very	O
low	O
frequencies	O
.	O
</s>
<s>
Because	O
of	O
this	O
,	O
most	O
PA	O
woofers	B-Device
are	O
not	O
well	O
suited	O
to	O
use	O
in	O
high	O
quality	O
high	O
fidelity	O
home	O
applications	O
,	O
and	O
vice	O
versa	O
.	O
</s>
<s>
To	O
accurately	O
reproduce	O
the	O
lowest	O
tones	O
,	O
a	O
woofer	B-Device
,	O
or	O
group	O
of	O
woofers	B-Device
,	O
must	O
move	O
an	O
appropriately	O
large	O
volume	O
of	O
air	O
⁠	O
—	O
⁠a	O
task	O
that	O
becomes	O
more	O
difficult	O
at	O
lower	O
frequencies	O
.	O
</s>
<s>
The	O
larger	O
the	O
room	O
,	O
the	O
more	O
air	O
the	O
woofer	B-Device
's	O
movement	O
will	O
have	O
to	O
displace	O
in	O
order	O
to	O
produce	O
the	O
required	O
sound	O
power	O
at	O
low	O
frequencies	O
.	O
</s>
