<s>
An	O
electrodynamic	B-Device
speaker	I-Device
driver	I-Device
,	O
often	O
called	O
simply	O
a	O
speaker	B-Device
driver	I-Device
when	O
the	O
type	O
is	O
implicit	O
,	O
is	O
an	O
individual	O
transducer	B-Algorithm
that	O
converts	O
an	O
electrical	O
audio	O
signal	O
to	O
sound	O
waves	O
.	O
</s>
<s>
While	O
the	O
term	O
is	O
sometimes	O
used	O
interchangeably	O
with	O
the	O
term	O
speaker	O
(	O
loudspeaker	O
)	O
,	O
it	O
is	O
usually	O
applied	O
to	O
specialized	O
transducers	B-Algorithm
which	O
reproduce	O
only	O
a	O
portion	O
of	O
the	O
audible	O
frequency	O
range	O
.	O
</s>
<s>
For	O
high	O
fidelity	O
reproduction	O
of	O
sound	O
,	O
multiple	O
loudspeakers	O
are	O
often	O
mounted	O
in	O
the	O
same	O
enclosure	B-Device
,	O
each	O
reproducing	O
a	O
different	O
part	O
of	O
the	O
audible	O
frequency	O
range	O
.	O
</s>
<s>
Drivers	O
made	O
for	O
reproducing	O
high	O
audio	O
frequencies	O
are	O
called	O
tweeters	B-Device
,	O
those	O
for	O
middle	O
frequencies	O
are	O
called	O
mid-range	B-Device
drivers	I-Device
,	O
and	O
those	O
for	O
low	O
frequencies	O
are	O
called	O
woofers	B-Device
,	O
while	O
those	O
for	O
very	O
low	O
bass	O
range	O
are	O
subwoofers	B-Application
.	O
</s>
<s>
Less	O
common	O
types	O
of	O
drivers	O
are	O
supertweeters	B-Device
and	O
rotary	B-Device
woofers	I-Device
.	O
</s>
<s>
The	O
electroacoustic	O
mechanism	O
most	O
widely	O
used	O
in	O
speakers	O
to	O
convert	O
the	O
electric	O
current	O
to	O
sound	O
waves	O
is	O
the	O
dynamic	O
or	O
electrodynamic	O
driver	O
,	O
invented	O
in	O
1925	O
by	O
Edward	O
W	O
.	O
Kellogg	O
and	O
Chester	O
W	O
.	O
Rice	O
,	O
which	O
creates	O
sound	O
with	O
a	O
coil	O
of	O
wire	O
called	O
a	O
voice	B-Device
coil	I-Device
suspended	O
between	O
the	O
poles	O
of	O
a	O
magnet	O
.	O
</s>
<s>
There	O
are	O
others	O
which	O
are	O
far	O
less	O
widely	O
used	O
:	O
electrostatic	B-Device
drivers	I-Device
,	O
piezoelectric	O
drivers	O
,	O
planar	O
magnetic	O
drivers	O
,	O
Heil	B-Device
air	I-Device
motion	I-Device
drivers	I-Device
,	O
and	O
ionic	B-Device
drivers	I-Device
,	O
among	O
others	O
.	O
</s>
<s>
Speaker	B-Device
drivers	I-Device
include	O
a	O
diaphragm	B-Device
that	O
moves	O
back	O
and	O
forth	O
to	O
create	O
pressure	O
waves	O
in	O
the	O
air	O
column	O
in	O
front	O
,	O
and	O
depending	O
on	O
the	O
application	O
,	O
at	O
some	O
angle	O
to	O
the	O
sides	O
.	O
</s>
<s>
The	O
diaphragm	B-Device
is	O
typically	O
in	O
the	O
shape	O
of	O
a	O
cone	O
for	O
low	O
and	O
mid	O
frequencies	O
or	O
a	O
dome	O
for	O
higher	O
frequencies	O
,	O
or	O
less	O
commonly	O
,	O
a	O
ribbon	O
,	O
and	O
is	O
usually	O
made	O
of	O
coated	O
or	O
uncoated	O
paper	O
or	O
polypropylene	O
plastic	O
.	O
</s>
<s>
All	O
speaker	B-Device
drivers	I-Device
have	O
a	O
means	O
of	O
electrically	O
inducing	O
back-and-forth	O
motion	O
.	O
</s>
<s>
Typically	O
there	O
is	O
a	O
tightly	O
wound	O
coil	O
of	O
insulated	O
wire	O
(	O
known	O
as	O
a	O
voice	B-Device
coil	I-Device
)	O
attached	O
to	O
the	O
neck	O
of	O
the	O
driver	O
's	O
cone	O
.	O
</s>
<s>
In	O
a	O
ribbon	O
speaker	O
the	O
voice	B-Device
coil	I-Device
may	O
be	O
printed	O
or	O
bonded	O
onto	O
a	O
sheet	O
of	O
very	O
thin	O
paper	O
,	O
aluminum	O
,	O
fiberglass	O
or	O
plastic	O
.	O
</s>
<s>
This	O
cone	O
,	O
dome	O
or	O
other	O
radiator	O
is	O
mounted	O
at	O
its	O
outer	O
edge	O
by	O
a	O
flexible	O
surround	O
to	O
a	O
rigid	O
frame	O
which	O
supports	O
a	O
permanent	O
magnet	O
in	O
close	O
proximity	O
to	O
the	O
voice	B-Device
coil	I-Device
.	O
</s>
<s>
For	O
the	O
sake	O
of	O
efficiency	O
the	O
relatively	O
lightweight	O
voice	B-Device
coil	I-Device
and	O
cone	O
are	O
the	O
moving	O
parts	O
of	O
the	O
driver	O
,	O
whereas	O
the	O
much	O
heavier	O
magnet	O
remains	O
stationary	O
.	O
</s>
<s>
Other	O
typical	O
components	O
are	O
a	O
spider	O
or	O
damper	O
,	O
used	O
as	O
the	O
rear	O
suspension	O
element	O
,	O
simple	O
terminals	O
or	O
binding	O
posts	O
to	O
connect	O
the	O
audio	O
signal	O
,	O
and	O
possibly	O
a	O
compliant	O
gasket	O
to	O
seal	O
the	O
joint	O
between	O
the	O
chassis	O
and	O
enclosure	B-Device
.	O
</s>
<s>
Drivers	O
are	O
almost	O
universally	O
mounted	O
into	O
a	O
rigid	O
enclosure	B-Device
of	O
wood	O
,	O
plastic	O
,	O
or	O
occasionally	O
metal	O
.	O
</s>
<s>
This	O
loudspeaker	B-Device
enclosure	I-Device
or	O
speaker	B-Device
box	I-Device
isolates	O
the	O
acoustic	O
energy	O
from	O
the	O
front	O
of	O
the	O
cone	O
from	O
that	O
of	O
the	O
back	O
of	O
the	O
cone	O
.	O
</s>
<s>
A	O
horn	B-Device
may	O
be	O
employed	O
to	O
increase	O
efficiency	O
and	O
directionality	O
.	O
</s>
<s>
A	O
grille	O
,	O
fabric	O
mesh	B-Algorithm
,	O
or	O
other	O
acoustically	O
neutral	O
screen	O
is	O
generally	O
provided	O
to	O
cosmetically	O
conceal	O
the	O
drivers	O
and	O
hardware	O
,	O
and	O
to	O
protect	O
the	O
driver	O
from	O
physical	O
damage	O
.	O
</s>
<s>
In	O
operation	O
,	O
a	O
signal	O
is	O
delivered	O
to	O
the	O
voice	B-Device
coil	I-Device
by	O
means	O
of	O
electrical	O
wires	O
,	O
from	O
the	O
amplifier	O
through	O
speaker	B-Device
cable	I-Device
,	O
then	O
through	O
flexible	O
tinsel	O
wire	O
to	O
the	O
moving	O
coil	O
.	O
</s>
<s>
The	O
current	O
creates	O
a	O
magnetic	O
field	O
that	O
causes	O
the	O
diaphragm	B-Device
to	O
be	O
alternately	O
forced	O
one	O
way	O
or	O
the	O
other	O
,	O
by	O
the	O
magnetic	O
field	O
produced	O
by	O
current	O
flowing	O
in	O
the	O
voice	B-Device
coil	I-Device
,	O
against	O
the	O
field	O
established	O
in	O
the	O
magnetic	O
gap	O
by	O
the	O
fixed	O
magnet	O
structure	O
as	O
the	O
electrical	O
signal	O
varies	O
.	O
</s>
<s>
The	O
resulting	O
back-and-forth	O
motion	O
drives	O
the	O
air	O
in	O
front	O
of	O
the	O
diaphragm	B-Device
,	O
resulting	O
in	O
pressure	O
differentials	O
that	O
travel	O
away	O
as	O
sound	O
waves	O
.	O
</s>
<s>
In	O
addition	O
,	O
each	O
contributes	O
to	O
centering	O
the	O
voice	B-Device
coil	I-Device
and	O
cone	O
,	O
both	O
concentrically	O
within	O
the	O
magnet	O
assembly	O
,	O
and	O
front-to-back	O
,	O
restoring	O
the	O
voice	B-Device
coil	I-Device
to	O
a	O
critical	O
position	O
within	O
the	O
magnetic	O
gap	O
,	O
neither	O
toward	O
one	O
end	O
nor	O
the	O
other	O
.	O
</s>
<s>
The	O
voice	B-Device
coil	I-Device
and	O
magnet	O
essentially	O
form	O
a	O
linear	O
motor	O
working	O
against	O
the	O
centering	O
"	O
spring	O
tension	O
"	O
of	O
the	O
spider	O
and	O
surround	O
.	O
</s>
<s>
If	O
there	O
were	O
no	O
restriction	O
on	O
travel	O
distance	O
imposed	O
by	O
the	O
spider	O
and	O
surround	O
,	O
the	O
voice	B-Device
coil	I-Device
could	O
be	O
ejected	O
from	O
the	O
magnet	O
assembly	O
at	O
high	O
power	O
levels	O
,	O
or	O
travel	O
inward	O
deep	O
enough	O
to	O
collide	O
with	O
the	O
back	O
of	O
the	O
magnet	O
assembly	O
.	O
</s>
<s>
The	O
majority	O
of	O
speaker	B-Device
drivers	I-Device
work	O
only	O
against	O
the	O
centering	O
forces	O
of	O
the	O
spider	O
and	O
surround	O
,	O
and	O
do	O
not	O
actively	O
monitor	B-Device
the	O
position	O
of	O
the	O
driver	O
element	O
or	O
attempt	O
to	O
precisely	O
position	O
it	O
.	O
</s>
<s>
Some	O
speaker	B-Device
driver	I-Device
designs	O
have	O
provisions	O
to	O
do	O
so	O
(	O
typically	O
termed	O
servomechanisms	O
)	O
;	O
these	O
are	O
generally	O
used	O
only	O
in	O
woofers	B-Device
and	O
especially	O
subwoofers	B-Application
,	O
due	O
to	O
the	O
greatly	O
increased	O
cone	O
excursions	O
required	O
at	O
those	O
frequencies	O
in	O
a	O
driver	O
whose	O
cone	O
size	O
is	O
well	O
under	O
the	O
wavelength	O
of	O
the	O
some	O
of	O
the	O
sounds	O
it	O
is	O
made	O
to	O
reproduce	O
(	O
ie	O
,	O
bass	O
frequencies	O
below	O
perhaps	O
100	O
Hz	O
or	O
so	O
)	O
.	O
</s>
<s>
Speaker	B-Device
drivers	I-Device
may	O
be	O
designed	O
to	O
operate	O
within	O
a	O
broad	O
or	O
narrow	O
frequency	O
range	O
.	O
</s>
<s>
Small	O
diaphragms	B-Device
are	O
not	O
well	O
suited	O
to	O
moving	O
the	O
large	O
volume	O
of	O
air	O
that	O
is	O
required	O
for	O
satisfying	O
low	O
frequency	O
response	O
.	O
</s>
<s>
Conversely	O
,	O
large	O
drivers	O
may	O
have	O
heavy	O
voice	B-Device
coils	I-Device
and	O
cones	O
that	O
limit	O
their	O
ability	O
to	O
move	O
at	O
very	O
high	O
frequencies	O
.	O
</s>
<s>
In	O
a	O
multi-way	O
loudspeaker	O
system	O
,	O
specialized	O
drivers	O
are	O
provided	O
to	O
produce	O
specific	O
frequency	O
ranges	O
,	O
and	O
the	O
incoming	O
signal	O
is	O
split	O
by	O
a	O
crossover	B-Algorithm
.	O
</s>
<s>
Drivers	O
can	O
be	O
sub-categorized	O
into	O
several	O
types	O
:	O
full-range	B-Device
,	O
tweeters	B-Device
,	O
super	B-Device
tweeters	I-Device
,	O
mid-range	B-Device
drivers	I-Device
,	O
woofers	B-Device
,	O
and	O
subwoofers	B-Application
.	O
</s>
<s>
Speaker	B-Device
drivers	I-Device
are	O
the	O
primary	O
means	O
for	O
sound	O
reproduction	O
.	O
</s>
<s>
They	O
are	O
used	O
among	O
other	O
places	O
in	O
audio	O
applications	O
such	O
as	O
loudspeakers	O
,	O
headphones	B-Device
,	O
telephones	O
,	O
megaphones	O
,	O
instrument	O
amplifiers	O
,	O
television	O
and	O
monitor	B-Device
speakers	O
,	O
public	O
address	O
systems	O
,	O
portable	O
radios	O
,	O
toys	O
,	O
and	O
in	O
many	O
electronics	O
devices	O
that	O
are	O
designed	O
to	O
emit	O
sound	O
.	O
</s>
