<s>
The	O
moving	B-Architecture
iron	I-Architecture
speaker	I-Architecture
was	O
the	O
earliest	O
type	O
of	O
electric	O
loudspeaker	O
.	O
</s>
<s>
A	O
moving	B-Architecture
iron	I-Architecture
speaker	I-Architecture
consists	O
of	O
a	O
ferrous-metal	O
diaphragm	O
or	O
reed	O
,	O
a	O
permanent	O
magnet	O
and	O
a	O
coil	O
of	O
insulated	O
wire	O
.	O
</s>
<s>
The	O
coil	O
is	O
wound	O
around	O
the	O
permanent	O
magnet	O
to	O
form	O
a	O
solenoid	B-Algorithm
.	O
</s>
<s>
There	O
are	O
several	O
types	O
of	O
moving	B-Architecture
iron	I-Architecture
speaker	I-Architecture
.	O
</s>
<s>
Modern	O
damped	O
moving	O
iron	O
mechanisms	O
can	O
provide	O
respectable	O
sound	O
quality	O
,	O
and	O
are	O
used	O
in	O
headphones	B-Device
.	O
</s>
<s>
Moving	O
iron	O
horn	B-Device
loudspeakers	I-Device
developed	O
from	O
earphones	O
after	O
the	O
first	O
amplifying	O
device	O
which	O
could	O
drive	O
a	O
speaker	O
,	O
the	O
triode	O
vacuum	O
tube	O
,	O
was	O
perfected	O
around	O
1913	O
.	O
</s>
<s>
Today	O
the	O
moving	O
iron	O
driver	O
mechanism	O
is	O
still	O
used	O
in	O
some	O
earphones	O
and	O
tiny	O
PC	B-Device
speakers	I-Device
.	O
</s>
<s>
Poor	O
bandwidth	B-Algorithm
and	O
modest	O
output	O
are	O
limitations	O
of	O
most	O
of	O
these	O
devices	O
.	O
</s>
<s>
The	O
cone	O
is	O
also	O
better	O
able	O
to	O
handle	O
lower	O
frequencies	O
compared	O
to	O
a	O
table-top	O
sized	O
horn	B-Device
.	O
</s>
<s>
Consequently	O
,	O
these	O
speakers	O
have	O
better	O
bass	O
response	O
than	O
small	O
horn	B-Device
speakers	I-Device
.	O
</s>
<s>
Paper	O
cone	O
loaded	O
moving	B-Architecture
iron	I-Architecture
speakers	I-Architecture
were	O
in	O
use	O
pre-war	O
.	O
</s>
<s>
Horn	B-Device
Horns	O
were	O
normally	O
driven	O
by	O
diaphragm	O
type	O
drivers	O
.	O
</s>
<s>
The	O
problem	O
with	O
horns	O
is	O
that	O
reasonable	O
bass	O
response	O
requires	O
impractical	O
horn	B-Device
size	O
,	O
and	O
the	O
table-top	O
sized	O
horns	O
popular	O
on	O
pre-war	O
speakers	O
were	O
thus	O
very	O
short	O
on	O
bass	O
response	O
.	O
</s>
<s>
Diaphragm	O
driven	O
horn	B-Device
speakers	I-Device
have	O
been	O
used	O
in	O
more	O
modern	O
times	O
as	O
midrange	O
squawkers	B-Device
and	O
tweeters	B-Device
,	O
frequency	O
ranges	O
which	O
they	O
are	O
capable	O
of	O
handling	O
properly	O
if	O
suitably	O
designed	O
.	O
</s>
<s>
This	O
sacrifices	O
bandwidth	B-Algorithm
for	O
sound	O
pressure	O
level	O
(	O
SPL	O
)	O
.	O
</s>
<s>
No	O
Loading	O
Moving	O
iron	O
transducers	O
used	O
in	O
headphones	B-Device
normally	O
have	O
no	O
attached	O
loading	O
(	O
no	O
cone	O
,	O
horn	B-Device
or	O
disc	O
)	O
.	O
</s>
<s>
The	O
volume	O
output	O
from	O
these	O
is	O
sufficient	O
for	O
headphone	B-Device
use	O
.	O
</s>
<s>
Balanced	O
armature	O
Balanced	O
armature	O
moving	B-Architecture
iron	I-Architecture
speakers	I-Architecture
were	O
developed	O
in	O
an	O
attempt	O
to	O
reduce	O
the	O
high	O
distortion	O
levels	O
of	O
single	O
ended	O
drive	O
speakers	O
.	O
</s>
<s>
Inductor	O
dynamic	O
moving	B-Architecture
iron	I-Architecture
speakers	I-Architecture
are	O
now	O
rare	O
.	O
</s>
<s>
A	O
lot	O
of	O
moving	B-Architecture
iron	I-Architecture
speakers	I-Architecture
have	O
no	O
damping	O
.	O
</s>
<s>
Modern	O
headphones	B-Device
that	O
use	O
this	O
technology	O
incorporate	O
damping	O
to	O
greatly	O
improve	O
sound	O
quality	O
.	O
</s>
<s>
Such	O
devices	O
can	O
be	O
used	O
on	O
valve	O
(	O
vacuum	O
tube	O
)	O
amplifiers	O
,	O
but	O
if	O
used	O
with	O
transistors	B-Application
some	O
precaution	O
to	O
prevent	O
overcurrent	O
at	O
low	O
frequency	O
is	O
often	O
necessary	O
,	O
such	O
as	O
a	O
series	O
resistor	O
or	O
capacitor	O
.	O
</s>
<s>
Undamped	O
moving	B-Architecture
iron	I-Architecture
speakers	I-Architecture
suffer	O
the	O
following	O
defects	O
:	O
</s>
<s>
Antique	O
pre-war	O
moving	B-Architecture
iron	I-Architecture
speakers	I-Architecture
also	O
suffered	O
the	O
following	O
defects	O
:	O
</s>
<s>
Impedance	O
Early	O
moving	B-Architecture
iron	I-Architecture
speakers	I-Architecture
were	O
normally	O
high	O
impedance	O
,	O
being	O
designed	O
to	O
be	O
connected	O
directly	O
to	O
the	O
output	O
triode	O
with	O
no	O
transformer	B-Algorithm
or	O
dc	O
blocking	O
.	O
</s>
<s>
However	O
,	O
when	O
using	O
a	O
moving	B-Architecture
iron	I-Architecture
speaker	I-Architecture
on	O
an	O
early	O
radio	O
,	O
dc	O
is	O
usually	O
present	O
,	O
and	O
either	O
the	O
polarity	O
marked	O
on	O
the	O
speaker	O
should	O
be	O
observed	O
,	O
or	O
means	O
used	O
to	O
remove	O
the	O
dc	O
component	O
from	O
the	O
speaker	O
.	O
</s>
<s>
Headphones	B-Device
Use	O
of	O
balanced	O
armature	O
mechanisms	O
is	O
common	O
in	O
modern	O
headphones	B-Device
.	O
</s>
