<s>
A	O
voice	B-Device
coil	I-Device
(	O
consisting	O
of	O
a	O
former	O
,	O
collar	O
,	O
and	O
winding	O
)	O
is	O
the	O
coil	O
of	O
wire	O
attached	O
to	O
the	O
apex	O
of	O
a	O
loudspeaker	B-Device
cone	O
.	O
</s>
<s>
The	O
term	O
is	O
also	O
used	O
for	O
voice	B-Device
coil	I-Device
linear	O
motors	O
such	O
as	O
those	O
used	O
to	O
move	O
the	O
heads	O
inside	O
hard	B-Device
disk	I-Device
drives	I-Device
,	O
which	O
produce	O
a	O
larger	O
force	O
and	O
move	O
a	O
longer	O
distance	O
but	O
work	O
on	O
the	O
same	O
principle	O
.	O
</s>
<s>
In	O
some	O
applications	O
,	O
such	O
as	O
electronic	O
focus	O
adjustment	O
on	O
digital	O
cameras	O
,	O
these	O
are	O
known	O
as	O
voice	B-Device
coil	I-Device
motors	O
(	O
VCM	O
)	O
.	O
</s>
<s>
By	O
driving	O
a	O
current	O
through	O
the	O
voice	B-Device
coil	I-Device
,	O
a	O
magnetic	O
field	O
is	O
produced	O
.	O
</s>
<s>
This	O
magnetic	O
field	O
causes	O
the	O
voice	B-Device
coil	I-Device
to	O
react	O
to	O
the	O
magnetic	O
field	O
from	O
a	O
permanent	O
magnet	O
fixed	O
to	O
the	O
speaker	O
's	O
frame	O
,	O
thereby	O
moving	O
the	O
cone	O
of	O
the	O
speaker	O
.	O
</s>
<s>
By	O
applying	O
an	O
audio	O
waveform	O
to	O
the	O
voice	B-Device
coil	I-Device
,	O
the	O
cone	O
will	O
reproduce	O
the	O
sound	O
pressure	O
waves	O
,	O
corresponding	O
to	O
the	O
original	O
input	O
signal	O
.	O
</s>
<s>
Because	O
the	O
moving	O
parts	O
of	O
the	O
speaker	O
must	O
be	O
of	O
low	O
mass	O
(	O
to	O
accurately	O
reproduce	O
high-frequency	O
sounds	O
without	O
being	O
damped	O
too	O
much	O
by	O
inertia	O
)	O
,	O
voice	B-Device
coils	I-Device
are	O
usually	O
made	O
as	O
light	O
weight	O
as	O
possible	O
,	O
making	O
them	O
delicate	O
.	O
</s>
<s>
Voice	B-Device
coils	I-Device
wound	O
with	O
flattened	O
wire	O
,	O
called	O
ribbon-wire	O
,	O
provide	O
a	O
higher	O
packing	O
density	O
in	O
the	O
magnetic	O
gap	O
than	O
coils	O
with	O
round	O
wire	O
.	O
</s>
<s>
The	O
majority	O
of	O
loudspeakers	O
use	O
'	O
overhung	O
 '	O
voice	B-Device
coils	I-Device
,	O
with	O
windings	O
that	O
are	O
taller	O
than	O
the	O
height	O
of	O
the	O
magnetic	O
gap	O
.	O
</s>
<s>
The	O
power	O
handling	O
is	O
limited	O
by	O
the	O
amount	O
of	O
heat	O
that	O
can	O
be	O
tolerated	O
,	O
and	O
the	O
amount	O
that	O
can	O
be	O
removed	O
from	O
the	O
voice	B-Device
coil	I-Device
.	O
</s>
<s>
If	O
all	O
other	O
conditions	O
remain	O
constant	O
,	O
the	O
area	O
of	O
the	O
voice	B-Device
coil	I-Device
windings	O
is	O
proportional	O
to	O
the	O
power	O
handling	O
of	O
the	O
coil	O
.	O
</s>
<s>
Thus	O
a	O
100mm	O
diameter	O
voice	B-Device
coil	I-Device
,	O
with	O
a	O
12mm	O
winding	O
height	O
has	O
similar	O
power	O
handling	O
to	O
a	O
50mm	O
diameter	O
voice	B-Device
coil	I-Device
with	O
a	O
24mm	O
winding	O
height	O
.	O
</s>
<s>
In	O
'	O
underhung	O
 '	O
voice	B-Device
coil	I-Device
designs	O
(	O
see	O
below	O
)	O
,	O
the	O
coil	O
is	O
shorter	O
than	O
the	O
magnetic	O
gap	O
,	O
a	O
topology	O
that	O
provides	O
consistent	O
electromotive	O
force	O
over	O
a	O
limited	O
range	O
of	O
motion	O
,	O
known	O
as	O
Xmax	O
.	O
</s>
<s>
Many	O
hi-fi	O
,	O
and	O
almost	O
all	O
professional	O
low	O
frequency	O
loudspeakers	O
(	O
woofers	O
)	O
include	O
vents	O
in	O
the	O
magnet	O
system	O
to	O
provide	O
forced-air	O
cooling	O
of	O
the	O
voice	B-Device
coil	I-Device
.	O
</s>
<s>
In	O
the	O
earliest	O
loudspeakers	O
,	O
voice	B-Device
coils	I-Device
were	O
wound	O
onto	O
paper	O
bobbins	O
,	O
which	O
was	O
appropriate	O
for	O
modest	O
power	O
levels	O
.	O
</s>
<s>
As	O
more	O
powerful	O
amplifiers	O
became	O
available	O
,	O
alloy	O
1145	O
aluminium	O
foil	O
was	O
widely	O
substituted	O
for	O
paper	O
bobbins	O
,	O
and	O
the	O
voice	B-Device
coils	I-Device
survived	O
increased	O
power	O
.	O
</s>
<s>
Typical	O
modern	O
hi-fi	O
loudspeaker	B-Device
voice	I-Device
coils	I-Device
employ	O
materials	O
which	O
can	O
withstand	O
operating	O
temperatures	O
up	O
to	O
150°C	O
,	O
or	O
even	O
180°C	O
.	O
</s>
<s>
For	O
professional	O
loudspeakers	O
,	O
advanced	O
thermoset	O
composite	O
materials	O
are	O
available	O
to	O
improve	O
voice	B-Device
coil	I-Device
survival	O
under	O
severe	O
simultaneous	O
thermal	O
(	O
<3	O
00°C	O
)	O
and	O
mechanical	O
stresses	O
.	O
</s>
<s>
It	O
rather	O
efficiently	O
but	O
inconveniently	O
transfers	O
heat	O
from	O
the	O
voice	B-Device
coil	I-Device
into	O
the	O
adhesive	O
bonds	O
of	O
the	O
loudspeaker	B-Device
,	O
thermally	O
degrading	O
or	O
even	O
burning	O
them	O
.	O
</s>
<s>
In	O
1955	O
DuPont	O
developed	O
Kapton	O
,	O
a	O
polyimide	O
plastic	O
film	O
which	O
did	O
not	O
suffer	O
from	O
aluminium	O
's	O
deficiencies	O
,	O
so	O
Kapton	O
,	O
and	O
later	O
Kaneka	O
Apical	O
were	O
widely	O
adopted	O
for	O
voice	B-Device
coils	I-Device
.	O
</s>
<s>
As	O
successful	O
as	O
these	O
dark	O
brown	O
plastic	O
films	O
were	O
for	O
most	O
hi-fi	O
voice	B-Device
coils	I-Device
,	O
they	O
also	O
had	O
some	O
less	O
attractive	O
properties	O
,	O
principally	O
their	O
cost	O
,	O
and	O
an	O
unfortunate	O
tendency	O
to	O
soften	O
when	O
hot	O
.	O
</s>
<s>
The	O
actual	O
wire	O
employed	O
in	O
voice	B-Device
coil	I-Device
winding	O
is	O
almost	O
always	O
copper	O
,	O
with	O
an	O
electrical	O
insulation	O
coating	O
,	O
and	O
in	O
some	O
cases	O
,	O
an	O
adhesive	O
overcoat	O
.	O
</s>
<s>
Copper	O
wire	O
provides	O
an	O
easily	O
manufactured	O
,	O
general	O
purpose	O
voice	B-Device
coil	I-Device
,	O
at	O
a	O
reasonable	O
cost	O
.	O
</s>
<s>
Where	O
maximum	O
sensitivity	O
or	O
extended	O
high	O
frequency	O
response	O
is	O
required	O
from	O
a	O
loudspeaker	B-Device
,	O
aluminium	O
wire	O
may	O
be	O
substituted	O
,	O
to	O
reduce	O
the	O
moving	O
mass	O
of	O
the	O
coil	O
.	O
</s>
<s>
Anodized	O
aluminium	O
flat	O
wire	O
may	O
be	O
used	O
,	O
providing	O
an	O
insulating	O
oxide	O
layer	O
more	O
resistant	O
to	O
dielectric	O
breakdown	O
than	O
enamel	O
coatings	O
on	O
other	O
voice	B-Device
coil	I-Device
wire	O
.	O
</s>
<s>
This	O
creates	O
lightweight	O
,	O
low-inductance	O
voice	B-Device
coils	I-Device
,	O
ideally	O
suited	O
to	O
use	O
in	O
small	O
,	O
extended	O
range	O
speakers	O
.	O
</s>
<s>
Voice	B-Device
coils	I-Device
can	O
be	O
used	O
for	O
applications	O
other	O
than	O
loudspeakers	O
,	O
where	O
time	O
force	O
linearity	O
and	O
long	O
strokes	O
are	O
needed	O
.	O
</s>
<s>
The	O
image	O
above	O
shows	O
two	O
ways	O
in	O
which	O
the	O
voice	B-Device
coil	I-Device
is	O
immersed	O
in	O
the	O
magnetic	O
field	O
.	O
</s>
<s>
The	O
most	O
common	O
method	O
is	O
the	O
overhung	O
design	O
where	O
the	O
height	O
of	O
the	O
voice	B-Device
coil	I-Device
is	O
greater	O
than	O
the	O
magnetic	O
gap	O
's	O
height	O
.	O
</s>
<s>
The	O
term	O
"	O
voice	B-Device
coil	I-Device
"	O
has	O
been	O
generalized	O
and	O
refers	O
to	O
any	O
galvanometer-like	O
mechanism	O
that	O
uses	O
a	O
solenoid	B-Algorithm
to	O
move	O
an	O
object	O
back-and-forth	O
within	O
a	O
magnetic	O
field	O
.	O
</s>
<s>
In	O
particular	O
,	O
it	O
is	O
commonly	O
used	O
to	O
refer	O
to	O
the	O
coil	O
of	O
wire	O
that	O
moves	O
the	O
read	O
–	O
write	O
heads	O
in	O
a	O
moving-head	O
disk	B-Device
drive	I-Device
.	O
</s>
<s>
The	O
voice	B-Device
coil	I-Device
is	O
the	O
motor	O
part	O
of	O
the	O
servo	O
system	O
that	O
positions	O
the	O
heads	O
:	O
an	O
electric	O
control	O
signal	O
drives	O
the	O
voice	B-Device
coil	I-Device
and	O
the	O
resulting	O
force	O
quickly	O
and	O
accurately	O
positions	O
the	O
heads	O
.	O
</s>
