<s>
Headphones	B-Device
are	O
a	O
pair	O
of	O
small	O
loudspeaker	B-Device
drivers	I-Device
worn	O
on	O
or	O
around	O
the	O
head	O
over	O
a	O
user	O
's	O
ears	O
.	O
</s>
<s>
They	O
are	O
electroacoustic	O
transducers	B-Algorithm
,	O
which	O
convert	O
an	O
electrical	O
signal	O
to	O
a	O
corresponding	O
sound	O
.	O
</s>
<s>
Headphones	B-Device
let	O
a	O
single	O
user	O
listen	O
to	O
an	O
audio	O
source	O
privately	O
,	O
in	O
contrast	O
to	O
a	O
loudspeaker	O
,	O
which	O
emits	O
sound	O
into	O
the	O
open	O
air	O
for	O
anyone	O
nearby	O
to	O
hear	O
.	O
</s>
<s>
Headphones	B-Device
are	O
also	O
known	O
as	O
earphones	O
or	O
,	O
colloquially	O
,	O
cans	O
.	O
</s>
<s>
Circumaural	O
( 	O
 '	O
around	O
the	O
ear	O
 '	O
)	O
and	O
supra-aural	O
( 	O
 '	O
over	O
the	O
ear	O
 '	O
)	O
headphones	B-Device
use	O
a	O
band	O
over	O
the	O
top	O
of	O
the	O
head	O
to	O
hold	O
the	O
speakers	O
in	O
place	O
.	O
</s>
<s>
Another	O
type	O
,	O
known	O
as	O
earbuds	O
or	O
earpieces	B-Device
consist	O
of	O
individual	O
units	O
that	O
plug	O
into	O
the	O
user	O
's	O
ear	O
canal	O
.	O
</s>
<s>
A	O
third	O
type	O
are	O
bone	O
conduction	O
headphones	B-Device
,	O
which	O
typically	O
wrap	O
around	O
the	O
back	O
of	O
the	O
head	O
and	O
rest	O
in	O
front	O
of	O
the	O
ear	O
canal	O
,	O
leaving	O
the	O
ear	O
canal	O
open	O
.	O
</s>
<s>
In	O
the	O
context	O
of	O
telecommunication	O
,	O
a	O
headset	B-Device
is	O
a	O
combination	O
of	O
headphone	B-Device
and	O
microphone	B-Application
.	O
</s>
<s>
Headphones	B-Device
connect	O
to	O
a	O
signal	O
source	O
such	O
as	O
an	O
audio	O
amplifier	O
,	O
radio	O
,	O
CD	B-Device
player	I-Device
,	O
portable	O
media	O
player	O
,	O
mobile	O
phone	O
,	O
video	B-Device
game	I-Device
console	I-Device
,	O
or	O
electronic	O
musical	O
instrument	O
,	O
either	O
directly	O
using	O
a	O
cord	O
,	O
or	O
using	O
wireless	O
technology	O
such	O
as	O
Bluetooth	B-Protocol
,	O
DECT	B-Protocol
or	O
FM	B-Application
radio	O
.	O
</s>
<s>
The	O
first	O
headphones	B-Device
were	O
developed	O
in	O
the	O
late	O
19th	O
century	O
for	O
use	O
by	O
telephone	O
operators	O
,	O
to	O
keep	O
their	O
hands	O
free	O
.	O
</s>
<s>
Initially	O
the	O
audio	O
quality	O
was	O
mediocre	O
and	O
a	O
step	O
forward	O
was	O
the	O
invention	O
of	O
high	O
fidelity	O
headphones	B-Device
.	O
</s>
<s>
Headphones	B-Device
exhibit	O
a	O
range	O
of	O
different	O
audio	O
reproduction	O
quality	O
capabilities	O
.	O
</s>
<s>
Headsets	B-Device
designed	O
for	O
telephone	O
use	O
typically	O
cannot	O
reproduce	O
sound	O
with	O
the	O
high	O
fidelity	O
of	O
expensive	O
units	O
designed	O
for	O
music	O
listening	O
by	O
audiophiles	O
.	O
</s>
<s>
Headphones	B-Device
that	O
use	O
cables	O
typically	O
have	O
either	O
a	O
or	O
phone	B-Device
jack	I-Device
for	O
plugging	O
the	O
headphones	B-Device
into	O
the	O
audio	O
source	O
.	O
</s>
<s>
Some	O
stereo	O
earbuds	O
are	O
wireless	O
,	O
using	O
Bluetooth	B-Protocol
connectivity	O
to	O
transmit	O
the	O
audio	O
signal	O
by	O
radio	O
waves	O
from	O
source	O
devices	O
like	O
cellphones	O
and	O
digital	O
players	O
.	O
</s>
<s>
As	O
a	O
result	O
of	O
the	O
Walkman	O
effect	O
,	O
beginning	O
in	O
the	O
1980s	O
,	O
headphones	B-Device
started	O
to	O
be	O
used	O
in	O
public	O
places	O
such	O
as	O
sidewalks	O
,	O
grocery	O
stores	O
,	O
and	O
public	O
transit	O
.	O
</s>
<s>
Headphones	B-Device
are	O
also	O
used	O
by	O
people	O
in	O
various	O
professional	O
contexts	O
,	O
such	O
as	O
audio	O
engineers	O
mixing	O
sound	O
for	O
live	O
concerts	O
or	O
sound	O
recordings	O
and	O
DJs	O
,	O
who	O
use	O
headphones	B-Device
to	O
cue	O
up	O
the	O
next	O
song	O
without	O
the	O
audience	O
hearing	O
,	O
aircraft	O
pilots	O
and	O
call	O
center	O
employees	O
.	O
</s>
<s>
The	O
latter	O
two	O
types	O
of	O
employees	O
use	O
headphones	B-Device
with	O
an	O
integrated	B-Application
microphone	I-Application
.	O
</s>
<s>
Headphones	B-Device
grew	O
out	O
of	O
the	O
need	O
to	O
free	O
up	O
a	O
person	O
's	O
hands	O
when	O
operating	O
a	O
telephone	O
.	O
</s>
<s>
There	O
were	O
several	O
iterative	O
products	O
that	O
were	O
predecessors	O
to	O
the	O
"	O
hands-free	O
"	O
headphones	B-Device
.	O
</s>
<s>
By	O
the	O
1890s	O
the	O
first	O
device	O
that	O
is	O
unmistakably	O
a	O
headphone	B-Device
was	O
made	O
by	O
a	O
British	O
company	O
called	O
Electrophone	O
,	O
which	O
created	O
a	O
system	O
allowing	O
their	O
customers	O
to	O
connect	O
into	O
live	O
feeds	O
of	O
performances	O
at	O
theaters	O
and	O
opera	O
houses	O
across	O
London	O
.	O
</s>
<s>
French	O
engineer	O
Ernest	O
Mercadier	O
patented	O
a	O
set	O
of	O
in-ear	B-Device
headphones	I-Device
in	O
1891	O
,	O
Mercadier	O
was	O
awarded	O
U.S.	O
Patent	O
No	O
.	O
</s>
<s>
Nathaniel	O
Baldwin	O
of	O
Utah	O
in	O
1910	O
invented	O
a	O
prototype	O
telephone	O
headset	B-Device
due	O
to	O
his	O
inability	O
to	O
hear	O
sermons	O
during	O
Sunday	O
service	O
.	O
</s>
<s>
Headphones	B-Device
originated	O
from	O
the	O
telephone	O
receiver	O
earpiece	B-Device
,	O
and	O
were	O
the	O
only	O
way	O
to	O
listen	O
to	O
electrical	O
audio	O
signals	O
before	O
amplifiers	O
were	O
developed	O
.	O
</s>
<s>
These	O
early	O
headphones	B-Device
used	O
moving	B-Architecture
iron	I-Architecture
drivers	I-Architecture
,	O
with	O
either	O
single-ended	O
or	O
balanced	O
armatures	O
.	O
</s>
<s>
The	O
common	O
single-ended	O
type	O
used	O
voice	B-Device
coils	I-Device
wound	O
around	O
the	O
poles	O
of	O
a	O
permanent	O
magnet	O
,	O
which	O
were	O
positioned	O
close	O
to	O
a	O
flexible	O
steel	O
diaphragm	B-Device
.	O
</s>
<s>
The	O
audio	O
current	O
through	O
the	O
coils	O
varied	O
the	O
magnetic	O
field	O
of	O
the	O
magnet	O
,	O
exerting	O
a	O
varying	O
force	O
on	O
the	O
diaphragm	B-Device
,	O
causing	O
it	O
to	O
vibrate	O
,	O
creating	O
sound	O
waves	O
.	O
</s>
<s>
The	O
requirement	O
for	O
high	O
sensitivity	O
meant	O
that	O
no	O
damping	O
was	O
used	O
,	O
so	O
the	O
frequency	O
response	O
of	O
the	O
diaphragm	B-Device
had	O
large	O
peaks	O
due	O
to	O
resonance	O
,	O
resulting	O
in	O
poor	O
sound	O
quality	O
.	O
</s>
<s>
Their	O
impedance	O
varied	O
;	O
headphones	B-Device
used	O
in	O
telegraph	O
and	O
telephone	O
work	O
had	O
an	O
impedance	O
of	O
75ohms	O
.	O
</s>
<s>
Some	O
very	O
sensitive	O
headphones	B-Device
,	O
such	O
as	O
those	O
manufactured	O
by	O
Brandes	O
around	O
1919	O
,	O
were	O
commonly	O
used	O
for	O
early	O
radio	O
work	O
.	O
</s>
<s>
In	O
early	O
powered	O
radios	O
,	O
the	O
headphone	B-Device
was	O
part	O
of	O
the	O
vacuum	O
tube	O
's	O
plate	O
circuit	O
and	O
carried	O
dangerous	O
voltages	O
.	O
</s>
<s>
The	O
use	O
of	O
bare	O
electrical	O
connections	O
meant	O
that	O
users	O
could	O
be	O
shocked	O
if	O
they	O
touched	O
the	O
bare	O
headphone	B-Device
connections	O
while	O
adjusting	O
an	O
uncomfortable	O
headset	B-Device
.	O
</s>
<s>
In	O
1958	O
,	O
John	O
C	O
.	O
Koss	O
,	O
an	O
audiophile	O
and	O
jazz	O
musician	B-Application
from	O
Milwaukee	O
,	O
produced	O
the	O
first	O
stereo	B-Device
headphones	I-Device
.	O
</s>
<s>
Smaller	O
earbud	O
type	O
earpieces	B-Device
,	O
which	O
plugged	O
into	O
the	O
user	O
's	O
ear	O
canal	O
,	O
were	O
first	O
developed	O
for	O
hearing	O
aids	O
.	O
</s>
<s>
The	O
3.5mm	O
radio	O
and	O
phone	B-Device
connector	I-Device
,	O
which	O
is	O
the	O
most	O
commonly	O
used	O
in	O
portable	O
application	O
today	O
,	O
has	O
been	O
used	O
at	O
least	O
since	O
the	O
Sony	O
EFM-117J	O
transistor	O
radio	O
,	O
which	O
was	O
released	O
in	O
1964	O
.	O
</s>
<s>
Headphones	B-Device
may	O
be	O
used	O
with	O
stationary	O
CD	O
and	O
DVD	B-Device
players	I-Device
,	O
home	O
theater	O
,	O
personal	B-Device
computers	I-Device
,	O
or	O
portable	O
devices	O
(	O
e.g.	O
,	O
digital	O
audio	O
player/MP3	O
player	O
,	O
mobile	O
phone	O
)	O
,	O
as	O
long	O
as	O
these	O
devices	O
are	O
equipped	O
with	O
a	O
headphone	B-Device
jack	I-Device
.	O
</s>
<s>
Cordless	O
headphones	B-Device
are	O
not	O
connected	O
to	O
their	O
source	O
by	O
a	O
cable	O
.	O
</s>
<s>
Instead	O
,	O
they	O
receive	O
a	O
radio	O
or	O
infrared	O
signal	O
encoded	O
using	O
a	O
radio	O
or	O
infrared	O
transmission	O
link	O
,	O
such	O
as	O
FM	B-Application
,	O
Bluetooth	B-Protocol
or	O
Wi-Fi	O
.	O
</s>
<s>
These	O
are	O
battery-powered	O
receiver	O
systems	O
,	O
of	O
which	O
the	O
headphone	B-Device
is	O
only	O
a	O
component	O
.	O
</s>
<s>
Cordless	O
headphones	B-Device
are	O
used	O
with	O
events	O
such	O
as	O
a	O
Silent	O
disco	O
or	O
Silent	O
Gig	O
.	O
</s>
<s>
In	O
the	O
professional	O
audio	O
sector	O
,	O
headphones	B-Device
are	O
used	O
in	O
live	O
situations	O
by	O
disc	O
jockeys	O
with	O
a	O
DJ	O
mixer	O
,	O
and	O
sound	O
engineers	O
for	O
monitoring	O
signal	O
sources	O
.	O
</s>
<s>
In	O
radio	O
studios	O
,	O
DJs	O
use	O
a	O
pair	B-Device
of	I-Device
headphones	I-Device
when	O
talking	O
to	O
the	O
microphone	B-Application
while	O
the	O
speakers	O
are	O
turned	O
off	O
to	O
eliminate	O
acoustic	O
feedback	O
while	O
monitoring	O
their	O
own	O
voice	O
.	O
</s>
<s>
In	O
studio	O
recordings	O
,	O
musicians	B-Application
and	O
singers	O
use	O
headphones	B-Device
to	O
play	O
or	O
sing	O
along	O
to	O
a	O
backing	O
track	O
or	O
band	O
.	O
</s>
<s>
In	O
military	O
applications	O
,	O
audio	O
signals	O
of	O
many	O
varieties	O
are	O
monitored	O
using	O
headphones	B-Device
.	O
</s>
<s>
Wired	O
headphones	B-Device
are	O
attached	O
to	O
an	O
audio	O
source	O
by	O
a	O
cable	O
.	O
</s>
<s>
The	O
most	O
common	O
connectors	O
are	O
6.35mm	O
(	O
inch	O
)	O
and	O
3.5mm	O
phone	B-Device
connectors	I-Device
.	O
</s>
<s>
As	O
active	O
component	O
,	O
wireless	B-Device
headphones	I-Device
tend	O
to	O
be	O
costlier	O
due	O
to	O
the	O
necessity	O
for	O
internal	O
hardware	O
such	O
as	O
a	O
battery	O
,	O
a	O
charging	O
controller	O
,	O
a	O
speaker	B-Device
driver	I-Device
,	O
and	O
a	O
wireless	O
transceiver	O
,	O
whereas	O
wired	O
headphones	B-Device
are	O
a	O
passive	O
component	O
,	O
outsourcing	O
speaker	O
driving	O
to	O
the	O
audio	O
source	O
.	O
</s>
<s>
Some	O
headphone	B-Device
cords	O
are	O
equipped	O
with	O
a	O
serial	O
potentiometer	B-Device
for	O
volume	B-Algorithm
control	O
.	O
</s>
<s>
Wired	O
headphones	B-Device
may	O
be	O
equipped	O
with	O
a	O
non-detachable	O
cable	O
or	O
a	O
detachable	O
auxiliary	O
male-to-male	O
plug	O
,	O
as	O
well	O
as	O
some	O
with	O
two	O
ports	O
to	O
allow	O
connecting	O
another	O
wired	O
headphone	B-Device
in	O
a	O
parallel	O
circuit	O
,	O
which	O
splits	O
the	O
audio	O
signal	O
to	O
share	O
with	O
another	O
participant	O
,	O
but	O
can	O
also	O
be	O
used	O
to	O
hear	O
audio	O
from	O
two	O
inputs	O
simultaneously	O
.	O
</s>
<s>
Various	O
types	O
of	O
specially	O
designed	O
headphones	B-Device
or	O
earphones	O
are	O
also	O
used	O
to	O
evaluate	O
the	O
status	O
of	O
the	O
auditory	O
system	O
in	O
the	O
field	O
of	O
audiology	O
for	O
establishing	O
hearing	O
thresholds	O
,	O
medically	O
diagnosing	O
hearing	O
loss	O
,	O
identifying	O
other	O
hearing	O
related	O
disease	O
,	O
and	O
monitoring	O
hearing	O
status	O
in	O
occupational	O
hearing	O
conservation	O
programs	O
.	O
</s>
<s>
Specific	O
models	O
of	O
headphones	B-Device
have	O
been	O
adopted	O
as	O
the	O
standard	O
due	O
to	O
the	O
ease	O
of	O
calibration	O
and	O
ability	O
to	O
compare	O
results	O
between	O
testing	O
facilities	O
.	O
</s>
<s>
Supra-aural	O
style	O
headphones	B-Device
are	O
historically	O
the	O
most	O
commonly	O
used	O
in	O
audiology	O
as	O
they	O
are	O
the	O
easiest	O
to	O
calibrate	O
and	O
were	O
considered	O
the	O
standard	O
for	O
many	O
years	O
.	O
</s>
<s>
Commonly	O
used	O
models	O
are	O
the	O
Telephonics	O
Dynamic	O
Headphone	B-Device
(	O
TDH	O
)	O
39	O
,	O
TDH-49	O
,	O
and	O
TDH-50	O
.	O
</s>
<s>
Audiometers	O
and	O
headphones	B-Device
must	O
be	O
calibrated	O
together	O
.	O
</s>
<s>
During	O
the	O
calibration	O
process	O
,	O
the	O
output	O
signal	O
from	O
the	O
audiometer	O
to	O
the	O
headphones	B-Device
is	O
measured	O
with	O
a	O
sound	O
level	O
meter	O
to	O
ensure	O
that	O
the	O
signal	O
is	O
accurate	O
to	O
the	O
reading	O
on	O
the	O
audiometer	O
for	O
sound	O
pressure	O
level	O
and	O
frequency	O
.	O
</s>
<s>
Calibration	O
is	O
done	O
with	O
the	O
earphones	O
in	O
an	O
acoustic	B-Device
coupler	I-Device
that	O
is	O
intended	O
to	O
mimic	O
the	O
transfer	O
function	O
of	O
the	O
outer	O
ear	O
.	O
</s>
<s>
Because	O
specific	O
headphones	B-Device
are	O
used	O
in	O
the	O
initial	O
audiometer	O
calibration	O
process	O
,	O
they	O
cannot	O
be	O
replaced	O
with	O
any	O
other	O
set	O
of	O
headphones	B-Device
,	O
even	O
from	O
the	O
same	O
make	O
and	O
model	O
.	O
</s>
<s>
Electrical	B-Architecture
characteristics	I-Architecture
of	I-Architecture
dynamic	I-Architecture
loudspeakers	I-Architecture
may	O
be	O
readily	O
applied	O
to	O
headphones	B-Device
,	O
because	O
most	O
headphones	B-Device
are	O
small	O
dynamic	O
loudspeakers	O
.	O
</s>
<s>
Headphones	B-Device
are	O
available	O
with	O
high	O
or	O
low	O
impedance	O
(	O
typically	O
measured	O
at	O
1kHz	O
)	O
.	O
</s>
<s>
Low-impedance	O
headphones	B-Device
are	O
in	O
the	O
range	O
16	O
to	O
32ohms	O
and	O
high-impedance	O
headphones	B-Device
are	O
about	O
100-600ohms	O
.	O
</s>
<s>
As	O
the	O
impedance	O
of	O
a	O
pair	B-Device
of	I-Device
headphones	I-Device
increases	O
,	O
more	O
voltage	O
(	O
at	O
a	O
given	O
current	O
)	O
is	O
required	O
to	O
drive	O
it	O
,	O
and	O
the	O
loudness	B-Algorithm
of	O
the	O
headphones	B-Device
for	O
a	O
given	O
voltage	O
decreases	O
.	O
</s>
<s>
In	O
recent	O
years	O
,	O
impedance	O
of	O
newer	O
headphones	B-Device
has	O
generally	O
decreased	O
to	O
accommodate	O
lower	O
voltages	O
available	O
on	O
battery	O
powered	O
CMOS-based	O
portable	O
electronics	O
.	O
</s>
<s>
This	O
has	O
resulted	O
in	O
headphones	B-Device
that	O
can	O
be	O
more	O
efficiently	O
driven	O
by	O
battery-powered	O
electronics	O
.	O
</s>
<s>
The	O
impedance	O
of	O
headphones	B-Device
is	O
of	O
concern	O
because	O
of	O
the	O
output	O
limitations	O
of	O
amplifiers	O
.	O
</s>
<s>
A	O
modern	O
pair	B-Device
of	I-Device
headphones	I-Device
is	O
driven	O
by	O
an	O
amplifier	O
,	O
with	O
lower	O
impedance	O
headphones	B-Device
presenting	O
a	O
larger	O
load	O
.	O
</s>
<s>
To	O
ensure	O
an	O
even	O
frequency	O
response	O
,	O
adequate	O
damping	O
factor	O
,	O
and	O
undistorted	O
sound	O
,	O
an	O
amplifier	O
should	O
have	O
an	O
output	O
impedance	O
less	O
than	O
1/8	O
that	O
of	O
the	O
headphones	B-Device
it	O
is	O
driving	O
(	O
and	O
ideally	O
,	O
as	O
low	O
as	O
possible	O
)	O
.	O
</s>
<s>
If	O
output	O
impedance	O
is	O
large	O
compared	O
to	O
the	O
impedance	O
of	O
the	O
headphones	B-Device
,	O
significantly	O
higher	O
distortion	O
is	O
present	O
.	O
</s>
<s>
Therefore	O
,	O
lower	O
impedance	O
headphones	B-Device
tend	O
to	O
be	O
louder	O
and	O
more	O
efficient	O
,	O
but	O
also	O
demand	O
a	O
more	O
capable	O
amplifier	O
.	O
</s>
<s>
Higher	O
impedance	O
headphones	B-Device
are	O
more	O
tolerant	O
of	O
amplifier	O
limitations	O
,	O
but	O
produce	O
less	O
volume	B-Algorithm
for	O
a	O
given	O
output	O
level	O
.	O
</s>
<s>
Historically	O
,	O
many	O
headphones	B-Device
had	O
relatively	O
high	O
impedance	O
,	O
often	O
over	O
500ohms	O
so	O
they	O
could	O
operate	O
well	O
with	O
high-impedance	O
tube	O
amplifiers	O
.	O
</s>
<s>
In	O
contrast	O
,	O
modern	O
transistor	O
amplifiers	O
can	O
have	O
very	O
low	O
output	O
impedance	O
,	O
enabling	O
lower-impedance	O
headphones	B-Device
.	O
</s>
<s>
Unfortunately	O
,	O
this	O
means	O
that	O
older	O
audio	O
amplifiers	O
or	O
stereos	O
often	O
produce	O
poor-quality	O
output	O
on	O
some	O
modern	O
,	O
low-impedance	O
headphones	B-Device
.	O
</s>
<s>
In	O
this	O
case	O
,	O
an	O
external	O
headphone	B-Device
amplifier	O
may	O
be	O
beneficial	O
.	O
</s>
<s>
Sensitivity	O
is	O
a	O
measure	O
of	O
how	O
effectively	O
an	O
earpiece	B-Device
converts	O
an	O
incoming	O
electrical	O
signal	O
into	O
an	O
audible	O
sound	O
.	O
</s>
<s>
It	O
thus	O
indicates	O
how	O
loud	O
the	O
headphones	B-Device
are	O
for	O
a	O
given	O
electrical	O
drive	O
level	O
.	O
</s>
<s>
As	O
the	O
output	O
voltage	O
(	O
but	O
not	O
power	O
)	O
of	O
a	O
headphone	B-Device
amplifier	O
is	O
essentially	O
constant	O
for	O
most	O
common	O
headphones	B-Device
,	O
dB/mW	O
is	O
often	O
more	O
useful	O
if	O
converted	O
into	O
dB/V	O
using	O
Ohm	O
's	O
law	O
:	O
</s>
<s>
Once	O
the	O
sensitivity	O
per	O
volt	O
is	O
known	O
,	O
the	O
maximum	O
volume	B-Algorithm
for	O
a	O
pair	B-Device
of	I-Device
headphones	I-Device
can	O
be	O
easily	O
calculated	O
from	O
the	O
maximum	O
amplifier	O
output	O
voltage	O
.	O
</s>
<s>
For	O
example	O
,	O
for	O
a	O
headphone	B-Device
with	O
a	O
sensitivity	O
of	O
100dB	O
(	O
SPL	O
)	O
/V	O
,	O
an	O
amplifier	O
with	O
an	O
output	O
of	O
1	O
root	B-General_Concept
mean	I-General_Concept
square	I-General_Concept
(	O
RMS	O
)	O
voltage	O
produces	O
a	O
maximum	O
volume	B-Algorithm
of	O
100dB	O
.	O
</s>
<s>
Pairing	O
high-sensitivity	O
headphones	B-Device
with	O
power	O
amplifiers	O
can	O
produce	O
dangerously	O
high	O
volumes	O
and	O
damage	O
headphones	B-Device
.	O
</s>
<s>
In	O
contrast	O
,	O
the	O
American	O
Occupational	O
Safety	O
and	O
Health	O
Administration	O
recommends	O
an	O
average	O
SPL	O
of	O
no	O
more	O
than	O
85dB(A )	O
to	O
avoid	O
long-term	O
hearing	O
loss	O
,	O
while	O
the	O
European	O
Union	O
standard	O
EN	O
50332-1:2013	O
recommends	O
that	O
volumes	O
above	O
85dB(A )	O
include	O
a	O
warning	O
,	O
with	O
an	O
absolute	O
maximum	O
volume	B-Algorithm
(	O
defined	O
using	O
40	O
–	O
4,000	O
Hz	O
noise	O
)	O
of	O
no	O
more	O
than	O
100dB	O
to	O
avoid	O
accidental	O
hearing	O
damage	O
.	O
</s>
<s>
Using	O
this	O
standard	O
,	O
headphones	B-Device
with	O
sensitivities	O
of	O
90	O
,	O
100	O
and	O
110dB	O
(	O
SPL	O
)	O
/V	O
should	O
be	O
driven	O
by	O
an	O
amplifier	O
capable	O
of	O
no	O
more	O
than	O
3.162	O
,	O
1.0	O
and	O
0.3162	O
RMS	O
volts	O
at	O
maximum	O
volume	B-Algorithm
setting	O
,	O
respectively	O
to	O
reduce	O
the	O
risk	O
of	O
hearing	O
damage	O
.	O
</s>
<s>
The	O
sensitivity	O
of	O
headphones	B-Device
is	O
usually	O
between	O
about	O
80	O
and	O
125dB/mW	O
and	O
usually	O
measured	O
at	O
1kHz	O
.	O
</s>
<s>
Headphone	B-Device
size	O
can	O
affect	O
the	O
balance	O
between	O
fidelity	O
and	O
portability	O
.	O
</s>
<s>
Generally	O
,	O
headphone	B-Device
form	O
factors	O
can	O
be	O
divided	O
into	O
four	O
separate	O
categories	O
:	O
circumaural	O
(	O
over-ear	O
)	O
,	O
supra-aural	O
(	O
on-ear	O
)	O
,	O
earbud	O
and	O
in-ear	O
.	O
</s>
<s>
Headphones	B-Device
with	O
soldered	O
headphone	B-Device
jack	I-Device
cables	O
.	O
</s>
<s>
Wireless	O
on-ear	O
headphones	B-Device
.	O
</s>
<s>
Often	O
have	O
an	O
inbuilt	O
headphone	B-Device
jack	I-Device
.	O
</s>
<s>
Wireless	O
over-ear	O
headphones	B-Device
.	O
</s>
<s>
Often	O
have	O
an	O
inbuilt	O
headphone	B-Device
jack	I-Device
.	O
</s>
<s>
True	O
wireless	B-Device
earbuds	I-Device
have	O
no	O
cord	O
to	O
keep	O
each	O
bud	O
connected	O
to	O
each	O
other	O
.	O
</s>
<s>
They	O
rely	O
on	O
wireless	O
technology	O
such	O
as	O
Bluetooth	B-Protocol
to	O
transmit	O
audio	O
from	O
a	O
hardware	O
device	O
.	O
</s>
<s>
Circumaural	O
headphones	B-Device
(	O
sometimes	O
called	O
full	O
size	O
headphones	B-Device
or	O
over-ear	O
headphones	B-Device
)	O
have	O
circular	O
or	O
ellipsoid	O
earpads	O
that	O
encompass	O
the	O
ears	O
.	O
</s>
<s>
Because	O
these	O
headphones	B-Device
completely	O
surround	O
the	O
ear	O
,	O
circumaural	O
headphones	B-Device
can	O
be	O
designed	O
to	O
fully	O
seal	O
against	O
the	O
head	O
to	O
attenuate	O
external	O
noise	O
.	O
</s>
<s>
Because	O
of	O
their	O
size	O
,	O
circumaural	O
headphones	B-Device
can	O
be	O
heavy	O
and	O
there	O
are	O
some	O
sets	O
that	O
weigh	O
over	O
.	O
</s>
<s>
Supra-aural	O
headphones	B-Device
or	O
on-ear	O
headphones	B-Device
have	O
pads	O
that	O
press	O
against	O
the	O
ears	O
,	O
rather	O
than	O
around	O
them	O
.	O
</s>
<s>
This	O
type	O
of	O
headphone	B-Device
generally	O
tends	O
to	O
be	O
smaller	O
and	O
lighter	O
than	O
circumaural	O
headphones	B-Device
,	O
resulting	O
in	O
less	O
attenuation	O
of	O
outside	O
noise	O
.	O
</s>
<s>
Supra-aural	O
headphones	B-Device
can	O
also	O
lead	O
to	O
discomfort	O
due	O
to	O
the	O
pressure	O
on	O
the	O
ear	O
as	O
compared	O
to	O
circumaural	O
headphones	B-Device
that	O
sit	O
around	O
the	O
ear	O
.	O
</s>
<s>
Earphones	O
are	O
very	O
small	O
headphones	B-Device
that	O
are	O
fitted	O
directly	O
in	O
the	O
outer	O
ear	O
,	O
facing	O
but	O
not	O
inserted	O
in	O
the	O
ear	O
canal	O
.	O
</s>
<s>
They	O
provide	O
hardly	O
any	O
acoustic	O
isolation	O
and	O
leave	O
room	O
for	O
ambient	O
noise	O
to	O
seep	O
in	O
;	O
users	O
may	O
turn	O
up	O
the	O
volume	B-Algorithm
dangerously	O
high	O
to	O
compensate	O
,	O
at	O
the	O
risk	O
of	O
causing	O
hearing	O
loss	O
.	O
</s>
<s>
In-ear	B-Device
headphones	I-Device
,	O
also	O
known	O
as	O
in-ear	B-Device
monitors	I-Device
(	O
IEMs	O
)	O
or	O
canalphones	O
,	O
are	O
small	O
headphones	B-Device
with	O
similar	O
portability	O
to	O
earbuds	O
that	O
are	O
inserted	O
in	O
the	O
ear	O
canal	O
itself	O
.	O
</s>
<s>
IEMs	O
are	O
higher-quality	O
in-ear	B-Device
headphones	I-Device
and	O
are	O
used	O
by	O
audio	O
engineers	O
and	O
musicians	B-Application
as	O
well	O
as	O
audiophiles	O
.	O
</s>
<s>
The	O
outer	O
shells	O
of	O
in-ear	B-Device
headphones	I-Device
are	O
made	O
up	O
of	O
a	O
variety	O
of	O
materials	O
,	O
such	O
as	O
plastic	O
,	O
aluminum	O
,	O
ceramic	O
and	O
other	O
metal	O
alloys	O
.	O
</s>
<s>
Because	O
in-ear	B-Device
headphones	I-Device
engage	O
the	O
ear	O
canal	O
,	O
they	O
can	O
be	O
prone	O
to	O
sliding	O
out	O
,	O
and	O
they	O
block	O
out	O
much	O
environmental	O
noise	O
.	O
</s>
<s>
Some	O
in-ear	B-Device
headphones	I-Device
utilize	O
built-in	O
microphones	B-Application
to	O
allow	O
some	O
outside	O
sound	O
to	O
be	O
heard	O
when	O
desired	O
.	O
</s>
<s>
Custom	O
in-ear	B-Device
headphones	I-Device
use	O
castings	O
of	O
the	O
ear	O
canal	O
to	O
create	O
custom-molded	O
plugs	O
that	O
provide	O
added	O
comfort	O
and	O
noise	O
isolation	O
.	O
</s>
<s>
Both	O
circumaural	O
and	O
supra-aural	O
headphones	B-Device
can	O
be	O
further	O
differentiated	O
by	O
the	O
type	O
of	O
earcups	O
:	O
</s>
<s>
Open-back	O
headphones	B-Device
have	O
the	O
back	O
of	O
the	O
earcups	O
open	O
.	O
</s>
<s>
This	O
leaks	O
more	O
sound	O
out	O
of	O
the	O
headphone	B-Device
and	O
also	O
lets	O
more	O
ambient	O
sounds	O
into	O
the	O
headphone	B-Device
,	O
but	O
gives	O
a	O
more	O
natural	O
or	O
speaker-like	O
sound	O
,	O
due	O
to	O
including	O
sounds	O
from	O
the	O
environment	O
.	O
</s>
<s>
Semi-open	O
headphones	B-Device
,	O
have	O
a	O
design	O
that	O
can	O
be	O
considered	O
as	O
a	O
compromise	O
between	O
open-back	O
headphones	B-Device
and	O
closed-back	O
headphones	B-Device
.	O
</s>
<s>
There	O
is	O
no	O
exact	O
definition	O
for	O
the	O
term	O
semi-open	O
headphone	B-Device
.	O
</s>
<s>
Where	O
the	O
open-back	O
approach	O
has	O
hardly	O
any	O
measure	O
to	O
block	O
sound	O
at	O
the	O
outer	O
side	O
of	O
the	O
diaphragm	B-Device
and	O
the	O
closed-back	O
approach	O
really	O
has	O
a	O
closed	O
chamber	O
at	O
the	O
outer	O
side	O
of	O
the	O
diaphragm	B-Device
,	O
a	O
semi-open	O
headphone	B-Device
can	O
have	O
a	O
chamber	O
to	O
partially	O
block	O
sound	O
while	O
letting	O
some	O
sound	O
through	O
via	O
openings	O
or	O
vents	O
.	O
</s>
<s>
Closed-back	O
headphones	B-Device
usually	O
can	O
produce	O
stronger	O
low	O
frequencies	O
than	O
open-back	O
headphones	B-Device
.	O
</s>
<s>
A	O
headset	B-Device
is	O
a	O
headphone	B-Device
combined	O
with	O
a	O
microphone	B-Application
.	O
</s>
<s>
Headsets	B-Device
provide	O
the	O
equivalent	O
functionality	O
of	O
a	O
telephone	O
handset	O
with	O
hands-free	O
operation	O
.	O
</s>
<s>
Among	O
applications	O
for	O
headsets	B-Device
,	O
besides	O
telephone	O
use	O
,	O
are	O
aviation	O
,	O
theatre	O
or	O
television	O
studio	O
intercom	O
systems	O
,	O
and	O
console	O
or	O
PC	O
gaming	O
.	O
</s>
<s>
Headsets	B-Device
are	O
made	O
with	O
either	O
a	O
single-earpiece	O
(	O
mono	O
)	O
or	O
a	O
double-earpiece	O
(	O
mono	O
to	O
both	O
ears	O
or	O
stereo	O
)	O
.	O
</s>
<s>
The	O
microphone	B-Application
arm	O
of	O
headsets	B-Device
is	O
either	O
an	O
external	O
microphone	B-Application
type	O
where	O
the	O
microphone	B-Application
is	O
held	O
in	O
front	O
of	O
the	O
user	O
's	O
mouth	O
,	O
or	O
a	O
voicetube	O
type	O
where	O
the	O
microphone	B-Application
is	O
housed	O
in	O
the	O
earpiece	B-Device
and	O
speech	O
reaches	O
it	O
by	O
means	O
of	O
a	O
hollow	O
tube	O
.	O
</s>
<s>
Telephone	O
headsets	B-Device
connect	O
to	O
a	O
fixed-line	B-Application
telephone	I-Application
system	O
.	O
</s>
<s>
A	O
telephone	O
headset	B-Device
functions	O
by	O
replacing	O
the	O
handset	O
of	O
a	O
telephone	O
.	O
</s>
<s>
Headsets	B-Device
for	O
standard	O
corded	O
telephones	O
are	O
fitted	O
with	O
a	O
standard	O
4P4C	O
commonly	O
called	O
an	O
RJ-9	O
connector	O
.	O
</s>
<s>
Headsets	B-Device
are	O
also	O
available	O
with	O
2.5mm	O
jack	O
sockets	O
for	O
many	O
DECT	B-Protocol
phones	O
and	O
other	O
applications	O
.	O
</s>
<s>
Cordless	O
bluetooth	B-Protocol
headsets	B-Device
are	O
available	O
,	O
and	O
often	O
used	O
with	O
mobile	O
telephones	O
.	O
</s>
<s>
Headsets	B-Device
are	O
widely	O
used	O
for	O
telephone-intensive	O
jobs	O
,	O
in	O
particular	O
by	O
call	O
centre	O
workers	O
.	O
</s>
<s>
For	O
older	O
models	O
of	O
telephones	O
,	O
the	O
headset	B-Device
microphone	B-Application
impedance	O
is	O
different	O
from	O
that	O
of	O
the	O
original	O
handset	O
,	O
requiring	O
a	O
telephone	O
amplifier	O
for	O
the	O
telephone	O
headset	B-Device
.	O
</s>
<s>
A	O
telephone	O
amplifier	O
provides	O
basic	O
pin-alignment	O
similar	O
to	O
a	O
telephone	O
headset	B-Device
adaptor	O
,	O
but	O
it	O
also	O
offers	O
sound	O
amplification	O
for	O
the	O
microphone	B-Application
as	O
well	O
as	O
the	O
loudspeakers	O
.	O
</s>
<s>
Most	O
models	O
of	O
telephone	O
amplifiers	O
offer	O
volume	B-Algorithm
control	O
for	O
loudspeaker	O
as	O
well	O
as	O
microphone	B-Application
,	O
mute	O
function	O
and	O
switching	O
between	O
headset	B-Device
and	O
handset	O
.	O
</s>
<s>
Communication	O
headsets	B-Device
are	O
used	O
for	O
two-way	O
communication	O
and	O
typically	O
consist	O
of	O
a	O
headphone	B-Device
and	O
attached	O
microphone	B-Application
.	O
</s>
<s>
Such	O
headsets	B-Device
are	O
used	O
in	O
a	O
variety	O
of	O
professions	O
as	O
aviation	O
,	O
military	O
,	O
sports	O
,	O
music	O
,	O
and	O
many	O
service-oriented	O
sectors	O
.	O
</s>
<s>
The	O
headphone	B-Device
types	O
that	O
provide	O
most	O
attenuation	O
are	O
in-ear	O
canal	O
headphones	B-Device
and	O
closed-back	O
headphones	B-Device
,	O
both	O
circumaural	O
and	O
supra	O
aural	O
.	O
</s>
<s>
Open-back	O
and	O
earbud	B-Device
headphones	I-Device
provide	O
some	O
passive	O
noise	O
isolation	O
,	O
but	O
much	O
less	O
than	O
the	O
others	O
.	O
</s>
<s>
Typical	O
closed-back	O
headphones	B-Device
block	O
8	O
to	O
12dB	O
,	O
and	O
in-ears	O
anywhere	O
from	O
10	O
to	O
15dB	O
.	O
</s>
<s>
Such	O
headphones	B-Device
claim	O
to	O
reduce	O
ambient	O
noise	O
by	O
around	O
25dB	O
.	O
</s>
<s>
Active	O
noise-cancelling	O
headphones	B-Device
use	O
a	O
microphone	B-Application
,	O
amplifier	O
,	O
and	O
speaker	O
to	O
pick	O
up	O
,	O
amplify	O
,	O
and	O
play	O
ambient	O
noise	O
in	O
phase-reversed	O
form	O
;	O
this	O
to	O
some	O
extent	O
cancels	O
out	O
unwanted	O
noise	O
from	O
the	O
environment	O
without	O
affecting	O
the	O
desired	O
sound	O
source	O
,	O
which	O
is	O
not	O
picked	O
up	O
and	O
reversed	O
by	O
the	O
microphone	B-Application
.	O
</s>
<s>
Active	O
noise	O
cancelling	O
headphones	B-Device
can	O
attenuate	O
ambient	O
noise	O
by	O
20dB	O
or	O
more	O
,	O
but	O
the	O
active	O
circuitry	O
is	O
mainly	O
effective	O
on	O
constant	O
sounds	O
and	O
at	O
lower	O
frequencies	O
,	O
rather	O
than	O
sharp	O
sounds	O
and	O
voices	O
.	O
</s>
<s>
Some	O
noise	O
cancelling	O
headphones	B-Device
are	O
designed	O
mainly	O
to	O
reduce	O
low-frequency	O
engine	O
and	O
travel	O
noise	O
in	O
aircraft	O
,	O
trains	O
,	O
and	O
automobiles	O
,	O
and	O
are	O
less	O
effective	O
in	O
environments	O
with	O
other	O
types	O
of	O
noise	O
.	O
</s>
<s>
Headphones	B-Device
use	O
various	O
types	O
of	O
transducer	B-Algorithm
to	O
convert	O
electrical	O
signals	O
to	O
sound	O
.	O
</s>
<s>
The	O
moving	O
coil	O
driver	O
,	O
more	O
commonly	O
referred	O
to	O
as	O
a	O
"	O
dynamic	O
"	O
driver	O
is	O
the	O
most	O
common	O
type	O
used	O
in	O
headphones	B-Device
.	O
</s>
<s>
It	O
consists	O
of	O
a	O
stationary	O
magnet	O
element	O
affixed	O
to	O
the	O
frame	O
of	O
the	O
headphone	B-Device
,	O
which	O
sets	O
up	O
a	O
static	O
magnetic	O
field	O
.	O
</s>
<s>
The	O
magnet	O
in	O
headphones	B-Device
is	O
typically	O
composed	O
of	O
ferrite	O
or	O
neodymium	O
.	O
</s>
<s>
A	O
voice	B-Device
coil	I-Device
,	O
a	O
light	O
coil	O
of	O
wire	O
,	O
is	O
suspended	O
in	O
the	O
magnetic	O
field	O
of	O
the	O
magnet	O
,	O
attached	O
to	O
a	O
diaphragm	B-Device
,	O
typically	O
fabricated	O
from	O
lightweight	O
,	O
high-stiffness-to-mass-ratio	O
cellulose	O
,	O
polymer	O
,	O
carbon	O
material	O
,	O
paper	O
or	O
the	O
like	O
.	O
</s>
<s>
When	O
the	O
varying	O
current	O
of	O
an	O
audio	O
signal	O
is	O
passed	O
through	O
the	O
coil	O
,	O
it	O
creates	O
a	O
varying	O
magnetic	O
field	O
that	O
reacts	O
against	O
the	O
static	O
magnetic	O
field	O
,	O
exerting	O
a	O
varying	O
force	O
on	O
the	O
coil	O
causing	O
it	O
and	O
the	O
attached	O
diaphragm	B-Device
to	O
vibrate	O
.	O
</s>
<s>
The	O
vibrating	O
diaphragm	B-Device
pushes	O
on	O
the	O
air	O
to	O
produce	O
sound	O
waves	O
.	O
</s>
<s>
Electrostatic	O
drivers	O
consist	O
of	O
a	O
thin	O
,	O
electrically	O
charged	O
diaphragm	B-Device
,	O
typically	O
a	O
coated	O
PET	O
film	O
membrane	O
,	O
suspended	O
between	O
two	O
perforated	O
metal	O
plates	O
(	O
electrodes	O
)	O
.	O
</s>
<s>
The	O
electrical	O
sound	O
signal	O
is	O
applied	O
to	O
the	O
electrodes	O
creating	O
an	O
electrical	O
field	O
;	O
depending	O
on	O
the	O
polarity	O
of	O
this	O
field	O
,	O
the	O
diaphragm	B-Device
is	O
drawn	O
towards	O
one	O
of	O
the	O
plates	O
.	O
</s>
<s>
Electrostatic	O
headphones	B-Device
are	O
usually	O
more	O
expensive	O
than	O
moving-coil	O
ones	O
,	O
and	O
are	O
comparatively	O
uncommon	O
.	O
</s>
<s>
Due	O
to	O
the	O
extremely	O
thin	O
and	O
light	O
diaphragm	B-Device
membrane	O
,	O
often	O
only	O
a	O
few	O
micrometers	O
thick	O
,	O
and	O
the	O
complete	O
absence	O
of	O
moving	O
metalwork	O
,	O
the	O
frequency	O
response	O
of	O
electrostatic	O
headphones	B-Device
usually	O
extends	O
well	O
above	O
the	O
audible	O
limit	O
of	O
approximately	O
20kHz	O
.	O
</s>
<s>
Well-designed	O
electrostatic	O
headphones	B-Device
can	O
produce	O
significantly	O
better	O
sound	O
quality	O
than	O
other	O
types	O
.	O
</s>
<s>
Electrostatic	O
headphones	B-Device
require	O
a	O
voltage	O
source	O
generating	O
100V	O
to	O
over	O
1kV	O
,	O
and	O
are	O
on	O
the	O
user	O
's	O
head	O
.	O
</s>
<s>
Electret	O
and	O
electrostatic	O
headphones	B-Device
are	O
relatively	O
uncommon	O
.	O
</s>
<s>
When	O
these	O
new	O
improved	O
electrets	O
are	O
combined	O
with	O
a	O
traditional	O
dome	O
headphone	B-Device
driver	O
,	O
headphones	B-Device
can	O
be	O
produced	O
that	O
are	O
recognised	O
by	O
the	O
Japan	O
Audio	O
Society	O
as	O
worthy	O
of	O
joining	O
the	O
Hi	O
Res	O
Audio	O
program	O
.	O
</s>
<s>
Planar	O
magnetic	O
(	O
also	O
known	O
as	O
orthodynamic	O
)	O
headphones	B-Device
use	O
similar	O
technology	O
to	O
electrostatic	O
headphones	B-Device
,	O
with	O
some	O
fundamental	O
differences	O
.	O
</s>
<s>
A	O
balanced	O
armature	O
is	O
a	O
sound	O
transducer	B-Algorithm
design	O
primarily	O
intended	O
to	O
increase	O
the	O
electrical	O
efficiency	O
of	O
the	O
element	O
by	O
eliminating	O
the	O
stress	O
on	O
the	O
diaphragm	B-Device
characteristic	O
of	O
many	O
other	O
magnetic	O
transducer	B-Algorithm
systems	O
.	O
</s>
<s>
As	O
illustrated	O
in	O
the	O
right	O
diagram	O
,	O
when	O
there	O
is	O
electric	O
current	O
through	O
the	O
coil	O
,	O
it	O
magnetizes	O
the	O
armature	O
one	O
way	O
or	O
the	O
other	O
,	O
causing	O
it	O
to	O
rotate	O
slightly	O
one	O
way	O
or	O
the	O
other	O
about	O
the	O
pivot	O
thus	O
moving	O
the	O
diaphragm	B-Device
to	O
make	O
sound	O
.	O
</s>
<s>
Popularized	O
in	O
the	O
1920s	O
as	O
Baldwin	O
Mica	O
Diaphragm	B-Device
radio	O
headphones	B-Device
,	O
balanced	O
armature	O
transducers	B-Algorithm
were	O
refined	O
during	O
World	O
War	O
II	O
for	O
use	O
in	O
military	O
sound	O
powered	O
telephones	O
.	O
</s>
<s>
Today	O
they	O
are	O
typically	O
used	O
only	O
in	O
in-ear	B-Device
headphones	I-Device
and	O
hearing	O
aids	O
,	O
where	O
their	O
high	O
efficiency	O
and	O
diminutive	O
size	O
is	O
a	O
major	O
advantage	O
.	O
</s>
<s>
Transducer	B-Algorithm
technologies	O
employed	O
much	O
less	O
commonly	O
for	O
headphones	B-Device
include	O
the	O
Heil	O
Air	B-Device
Motion	I-Device
Transformer	I-Device
(	O
AMT	O
)	O
;	O
Piezoelectric	O
film	O
;	O
Ribbon	O
planar	O
magnetic	O
;	O
Magnetostriction	O
and	O
Plasma	B-Device
or	I-Device
Ionic	I-Device
.	O
</s>
<s>
The	O
first	O
Heil	B-Device
AMT	I-Device
headphone	B-Device
was	O
marketed	O
by	O
ESS	O
Laboratories	O
and	O
was	O
essentially	O
an	O
ESS	O
AMT	O
tweeter	O
from	O
one	O
of	O
the	O
company	O
's	O
speakers	O
being	O
driven	O
at	O
full	O
range	O
.	O
</s>
<s>
Since	O
the	O
turn	O
of	O
the	O
century	O
,	O
only	O
Precide	O
of	O
Switzerland	O
have	O
manufactured	O
an	O
AMT	O
headphone	B-Device
.	O
</s>
<s>
Piezoelectric	O
film	O
headphones	B-Device
were	O
first	O
developed	O
by	O
Pioneer	O
,	O
their	O
two	O
models	O
used	O
a	O
flat	O
sheet	O
of	O
film	O
that	O
limited	O
the	O
maximum	O
volume	B-Algorithm
of	O
air	O
movement	O
.	O
</s>
<s>
Currently	O
,	O
TakeT	O
produces	O
a	O
piezoelectric	O
film	O
headphone	B-Device
shaped	O
similarly	O
to	O
an	O
AMT	O
transducer	B-Algorithm
but	O
,	O
which	O
like	O
the	O
Precide	O
driver	O
,	O
has	O
a	O
variation	O
in	O
the	O
size	O
of	O
transducer	B-Algorithm
folds	O
over	O
the	O
diaphragm	B-Device
.	O
</s>
<s>
The	O
folded	O
shape	O
of	O
a	O
diaphragm	B-Device
allows	O
a	O
transducer	B-Algorithm
with	O
a	O
larger	O
surface	O
area	O
to	O
fit	O
within	O
smaller	O
space	O
constraints	O
.	O
</s>
<s>
This	O
increases	O
the	O
total	O
volume	B-Algorithm
of	O
air	O
that	O
can	O
be	O
moved	O
on	O
each	O
excursion	O
of	O
the	O
transducer	B-Algorithm
given	O
that	O
radiating	O
area	O
.	O
</s>
<s>
Due	O
to	O
the	O
small	O
volume	B-Algorithm
of	O
air	O
in	O
a	O
headphone	B-Device
,	O
the	O
plasma	B-Device
or	I-Device
ionic	I-Device
transducer	B-Algorithm
can	O
become	O
a	O
full	O
range	O
driver	O
although	O
the	O
high	O
temperatures	O
and	O
voltages	O
of	O
these	O
types	O
makes	O
them	O
very	O
rare	O
with	O
only	O
the	O
Plasmasonic	O
being	O
commercial	O
.	O
</s>
<s>
Magnetostriction	O
headphones	B-Device
,	O
sometimes	O
sold	O
under	O
the	O
label	O
Bonephones	O
,	O
work	O
by	O
vibrating	O
against	O
the	O
side	O
of	O
head	O
,	O
transmitting	O
sound	O
via	O
bone	O
conduction	O
.	O
</s>
<s>
Magnetostriction	O
headphones	B-Device
though	O
,	O
are	O
limited	O
in	O
their	O
fidelity	O
compared	O
to	O
conventional	O
headphones	B-Device
that	O
rely	O
on	O
the	O
normal	O
workings	O
of	O
the	O
ear	O
.	O
</s>
<s>
Additionally	O
,	O
in	O
the	O
mid-1980s	O
,	O
a	O
French	O
company	O
called	O
Audio	O
Reference	O
tried	O
to	O
market	O
the	O
Plasmasonic	O
plasma	O
headphone	B-Device
invented	O
by	O
Henri	O
Bondar	O
.	O
</s>
<s>
Due	O
to	O
the	O
small	O
volume	B-Algorithm
of	O
air	O
in	O
a	O
headphone	B-Device
,	O
the	O
plasma	B-Device
or	I-Device
ionic	I-Device
transducer	B-Algorithm
can	O
become	O
a	O
full	O
range	O
driver	O
although	O
the	O
high	O
temperatures	O
and	O
voltages	O
needed	O
makes	O
them	O
very	O
rare	O
.	O
</s>
<s>
Headphones	B-Device
can	O
prevent	O
other	O
people	O
from	O
hearing	O
the	O
sound	O
,	O
either	O
for	O
privacy	O
or	O
to	O
prevent	O
disturbing	O
others	O
,	O
as	O
in	O
listening	O
in	O
a	O
public	O
library	O
.	O
</s>
<s>
Part	O
of	O
their	O
ability	O
to	O
do	O
so	O
comes	O
from	O
the	O
lack	O
of	O
any	O
need	O
to	O
perform	O
room	O
correction	O
treatments	O
with	O
headphones	B-Device
.	O
</s>
<s>
High-quality	O
headphones	B-Device
can	O
have	O
an	O
extremely	O
flat	O
low-frequency	O
response	O
down	O
to	O
20Hz	O
within	O
3dB	O
.	O
</s>
<s>
While	O
a	O
loudspeaker	O
must	O
use	O
a	O
relatively	O
large	O
(	O
often	O
15	O
"	O
or	O
18	O
"	O
)	O
speaker	B-Device
driver	I-Device
to	O
reproduce	O
low	O
frequencies	O
,	O
headphones	B-Device
can	O
accurately	O
reproduce	O
bass	O
and	O
sub-bass	O
frequencies	O
with	O
speaker	B-Device
drivers	I-Device
only	O
40-50	O
millimeters	O
wide	O
(	O
or	O
much	O
smaller	O
,	O
as	O
is	O
the	O
case	O
with	O
in-ear	B-Device
monitor	I-Device
headphones	B-Device
)	O
.	O
</s>
<s>
Headphones	B-Device
 '	O
impressive	O
low-frequency	O
performance	O
is	O
possible	O
because	O
they	O
are	O
so	O
much	O
closer	O
to	O
the	O
ear	O
that	O
they	O
only	O
need	O
to	O
move	O
relatively	O
small	O
volumes	O
of	O
air	O
.	O
</s>
<s>
Headphones	B-Device
are	O
also	O
useful	O
for	O
video	O
games	O
that	O
use	O
3D	O
positional	O
audio	O
processing	O
algorithms	O
,	O
as	O
they	O
allow	O
players	O
to	O
better	O
judge	O
the	O
position	O
of	O
an	O
off-screen	O
sound	O
source	O
(	O
such	O
as	O
the	O
footsteps	O
of	O
an	O
opponent	O
or	O
their	O
gunfire	O
)	O
.	O
</s>
<s>
Although	O
modern	O
headphones	B-Device
have	O
been	O
particularly	O
widely	O
sold	O
and	O
used	O
for	O
listening	O
to	O
stereo	O
recordings	O
since	O
the	O
release	O
of	O
the	O
Walkman	O
,	O
there	O
is	O
subjective	O
debate	O
regarding	O
the	O
nature	O
of	O
their	O
reproduction	O
of	O
stereo	O
sound	O
.	O
</s>
<s>
Stereo	O
recordings	O
represent	O
the	O
position	O
of	O
horizontal	O
depth	O
cues	O
(	O
stereo	O
separation	O
)	O
via	O
volume	B-Algorithm
and	O
phase	O
differences	O
of	O
the	O
sound	O
in	O
question	O
between	O
the	O
two	O
channels	O
.	O
</s>
<s>
Through	O
most	O
headphones	B-Device
,	O
because	O
the	O
right	O
and	O
left	O
channels	O
do	O
not	O
combine	O
in	O
this	O
manner	O
,	O
the	O
illusion	O
of	O
the	O
phantom	O
center	O
can	O
be	O
perceived	O
as	O
lost	O
.	O
</s>
<s>
Binaural	O
recordings	O
use	O
a	O
different	O
microphone	B-Application
technique	O
to	O
encode	O
direction	O
directly	O
as	O
phase	O
,	O
with	O
very	O
little	O
amplitude	O
difference	O
below	O
2kHz	O
,	O
often	O
using	O
a	O
dummy	O
head	O
.	O
</s>
<s>
They	O
can	O
produce	O
a	O
surprisingly	O
lifelike	O
spatial	O
impression	O
through	O
headphones	B-Device
.	O
</s>
<s>
Commercial	O
recordings	O
almost	O
always	O
use	O
stereo	O
recording	O
,	O
rather	O
than	O
binaural	O
,	O
because	O
loudspeaker	O
listening	O
is	O
more	O
common	O
than	O
headphone	B-Device
listening	O
.	O
</s>
<s>
It	O
is	O
possible	O
to	O
change	O
the	O
spatial	O
effects	O
of	O
stereo	O
sound	O
on	O
headphones	B-Device
,	O
to	O
better	O
approximate	O
the	O
presentation	O
of	O
speaker	O
reproduction	O
,	O
by	O
using	O
frequency-dependent	O
cross-feed	O
between	O
the	O
channels	O
.	O
</s>
<s>
Headsets	B-Device
can	O
have	O
ergonomic	O
benefits	O
over	O
traditional	O
telephone	O
handsets	O
.	O
</s>
<s>
Using	O
headphones	B-Device
at	O
a	O
sufficiently	O
high	O
volume	B-Algorithm
level	O
may	O
cause	O
temporary	O
or	O
permanent	O
hearing	O
impairment	O
or	O
deafness	O
.	O
</s>
<s>
The	O
headphone	B-Device
volume	B-Algorithm
often	O
has	O
to	O
compete	O
with	O
the	O
background	O
noise	O
,	O
especially	O
in	O
loud	O
places	O
such	O
as	O
subway	O
stations	O
,	O
aircraft	O
,	O
and	O
large	O
crowds	O
.	O
</s>
<s>
Extended	O
periods	O
of	O
exposure	O
to	O
high	O
sound	O
pressure	O
levels	O
created	O
by	O
headphones	B-Device
at	O
high	O
volume	B-Algorithm
settings	O
may	O
be	O
damaging	O
to	O
hearing	O
;	O
Nearly	O
50%	O
of	O
teenagers	O
and	O
young	O
adults	O
(	O
12	O
to	O
35	O
years	O
old	O
)	O
in	O
middle	O
and	O
high	O
income	O
countries	O
listen	O
to	O
unsafe	O
levels	O
of	O
sound	O
on	O
their	O
personal	O
audio	O
devices	O
and	O
smartphones	B-Application
.	O
</s>
<s>
However	O
,	O
one	O
hearing	O
expert	O
found	O
in	O
2012	O
(	O
before	O
the	O
worldwide	O
adoption	O
of	O
smartphones	B-Application
as	O
the	O
main	O
personal	O
listening	O
devices	O
)	O
that	O
"	O
fewer	O
than	O
5%	O
of	O
users	O
select	O
volume	B-Algorithm
levels	O
and	O
listen	O
frequently	O
enough	O
to	O
risk	O
hearing	O
loss.	O
"	O
</s>
<s>
Most	O
major	O
manufactures	O
of	O
smartphones	B-Application
now	O
include	O
some	O
safety	O
or	O
volume	B-Algorithm
limiting	O
features	O
and	O
warning	O
messaging	O
in	O
their	O
devices	O
.	O
</s>
<s>
though	O
such	O
practices	O
have	O
received	O
mixed	O
response	O
from	O
some	O
segments	O
of	O
the	O
buying	O
who	O
favor	O
the	O
personal	O
choice	O
of	O
setting	O
their	O
own	O
volume	B-Algorithm
levels	O
.	O
</s>
<s>
The	O
usual	O
way	O
of	O
limiting	O
sound	O
volume	B-Algorithm
on	O
devices	O
driving	O
headphones	B-Device
is	O
by	O
limiting	O
output	O
power	O
.	O
</s>
<s>
This	O
has	O
the	O
additional	O
undesirable	O
effect	O
of	O
being	O
dependent	O
of	O
the	O
efficiency	O
of	O
the	O
headphones	B-Device
;	O
a	O
device	O
producing	O
the	O
maximum	O
allowed	O
power	O
may	O
not	O
produce	O
adequate	O
volume	B-Algorithm
when	O
paired	O
with	O
low-efficiency	O
,	O
high-impedance	O
equipment	O
,	O
while	O
the	O
same	O
amount	O
of	O
power	O
can	O
reach	O
dangerous	O
levels	O
with	O
very	O
efficient	O
earphones	O
.	O
</s>
<s>
A	O
Finnish	O
study	O
recommended	O
that	O
exercisers	O
should	O
set	O
their	O
headphone	B-Device
volumes	O
to	O
half	O
of	O
their	O
normal	O
loudness	B-Algorithm
and	O
only	O
use	O
them	O
for	O
half	O
an	O
hour	O
.	O
</s>
<s>
Other	O
than	O
hearing	O
risk	O
,	O
there	O
is	O
a	O
general	O
danger	O
that	O
listening	O
to	O
loud	O
music	O
in	O
headphones	B-Device
can	O
distract	O
the	O
listener	O
and	O
lead	O
to	O
injury	O
and	O
accidents	O
.	O
</s>
<s>
Noise-cancelling	O
headphones	B-Device
add	O
extra	O
risk	O
.	O
</s>
<s>
Several	O
countries	O
and	O
states	O
have	O
made	O
it	O
illegal	O
to	O
wear	O
headphones	B-Device
while	O
driving	O
or	O
cycling	O
.	O
</s>
<s>
There	O
have	O
also	O
been	O
numerous	O
reports	O
of	O
contact	O
dermatitis	O
due	O
to	O
exposure	O
to	O
in-ear	B-Device
headphones	I-Device
such	O
as	O
Apple	O
AirPods	O
.	O
</s>
<s>
The	O
contact	O
dermatitis	O
would	O
be	O
caused	O
by	O
in-ear	B-Device
headphones	I-Device
that	O
contain	O
gold	O
,	O
rubber	O
,	O
dyes	O
,	O
acrylates	O
,	O
or	O
methacrylates	O
.	O
</s>
<s>
However	O
,	O
there	O
have	O
been	O
no	O
studies	O
done	O
to	O
prove	O
that	O
exposure	O
to	O
in-ear	B-Device
headphones	I-Device
will	O
cause	O
contact	O
dermatitis	O
,	O
rather	O
that	O
there	O
is	O
a	O
correlation	O
between	O
in-ear	O
headphone	B-Device
use	O
and	O
contact	O
dermatitis	O
cases	O
.	O
</s>
<s>
Hearing	O
risk	O
from	O
headphones	B-Device
 '	O
use	O
also	O
applies	O
to	O
workers	O
who	O
must	O
wear	O
electronic	O
or	O
communication	O
headsets	B-Device
as	O
part	O
of	O
their	O
daily	O
job	O
(	O
i.e.	O
,	O
pilots	O
,	O
call	O
center	O
and	O
dispatch	O
operators	O
,	O
sound	O
engineers	O
,	O
firefighters	O
,	O
etc	O
.	O
)	O
</s>
<s>
NIOSH	O
published	O
several	O
documents	O
targeted	O
at	O
protecting	O
the	O
hearing	O
of	O
workers	O
who	O
must	O
wear	O
communication	O
headsets	B-Device
such	O
as	O
call	O
center	O
operators	O
,	O
firefighters	O
,	O
and	O
musicians	B-Application
and	O
sound	O
engineers	O
.	O
</s>
