<s>
A	O
tweeter	B-Device
or	O
treble	O
speaker	O
is	O
a	O
special	O
type	O
of	O
loudspeaker	O
(	O
usually	O
dome	O
,	O
inverse	O
dome	O
or	O
horn-type	O
)	O
that	O
is	O
designed	O
to	O
produce	O
high	O
audio	O
frequencies	O
,	O
typically	O
deliver	O
high	O
frequencies	O
up	O
to	O
100kHz	O
.	O
</s>
<s>
The	O
name	O
is	O
derived	O
from	O
the	O
high	O
pitched	O
sounds	O
made	O
by	O
some	O
birds	O
(	O
tweets	O
)	O
,	O
especially	O
in	O
contrast	O
to	O
the	O
low	O
woofs	O
made	O
by	O
many	O
dogs	O
,	O
after	O
which	O
low-frequency	O
drivers	O
are	O
named	O
(	O
woofers	B-Device
)	O
.	O
</s>
<s>
Nearly	O
all	O
tweeters	B-Device
are	O
electrodynamic	O
drivers	O
using	O
a	O
voice	B-Device
coil	I-Device
suspended	O
within	O
a	O
fixed	O
magnetic	O
field	O
.	O
</s>
<s>
These	O
designs	O
operate	O
by	O
applying	O
current	O
from	O
the	O
output	O
of	O
an	O
amplifier	O
circuit	O
to	O
a	O
coil	O
of	O
wire	O
called	O
a	O
voice	B-Device
coil	I-Device
.	O
</s>
<s>
The	O
voice	B-Device
coil	I-Device
produces	O
a	O
varying	O
magnetic	O
field	O
,	O
which	O
works	O
against	O
the	O
fixed	O
magnetic	O
field	O
of	O
a	O
permanent	O
magnet	O
around	O
which	O
the	O
cylindrical	O
voice	B-Device
coil	I-Device
is	O
suspended	O
,	O
forcing	O
the	O
voice	B-Device
coil	I-Device
and	O
the	O
diaphragm	O
attached	O
to	O
it	O
to	O
move	O
.	O
</s>
<s>
This	O
mechanical	O
movement	O
resembles	O
the	O
waveform	O
of	O
the	O
electronic	O
signal	O
supplied	O
from	O
the	O
amplifier	O
's	O
output	O
to	O
the	O
voice	B-Device
coil	I-Device
.	O
</s>
<s>
Since	O
the	O
coil	O
is	O
attached	O
to	O
a	O
diaphragm	O
,	O
the	O
vibratory	O
motion	O
of	O
the	O
voice	B-Device
coil	I-Device
transmits	O
to	O
the	O
diaphragm	O
;	O
the	O
diaphragm	O
in	O
turn	O
vibrates	O
the	O
air	O
,	O
thus	O
creating	O
air	O
motions	O
or	O
audio	O
waves	O
,	O
which	O
is	O
heard	O
as	O
high	O
sounds	O
.	O
</s>
<s>
Modern	O
tweeters	B-Device
are	O
typically	O
different	O
from	O
older	O
tweeters	B-Device
,	O
which	O
were	O
usually	O
small	O
versions	O
of	O
woofers	B-Device
.	O
</s>
<s>
As	O
tweeter	B-Device
technology	O
has	O
advanced	O
,	O
different	O
design	O
applications	O
have	O
become	O
popular	O
.	O
</s>
<s>
Many	O
soft	B-Device
dome	I-Device
tweeter	I-Device
diaphragms	O
are	O
thermoformed	O
from	O
polyester	O
film	O
,	O
or	O
silk	O
or	O
polyester	O
fabric	O
that	O
has	O
been	O
impregnated	O
with	O
a	O
polymer	O
resin	O
.	O
</s>
<s>
Hard	O
dome	O
tweeters	B-Device
are	O
usually	O
made	O
of	O
aluminium	O
,	O
aluminium-magnesium	O
alloys	O
,	O
or	O
titanium	O
.	O
</s>
<s>
Tweeters	B-Device
are	O
intended	O
to	O
convert	O
an	O
electrical	O
signal	O
into	O
mechanical	O
air	O
movement	O
with	O
nothing	O
added	O
or	O
subtracted	O
,	O
but	O
the	O
process	O
is	O
imperfect	O
,	O
and	O
real-world	O
tweeters	B-Device
involve	O
tradeoffs	O
.	O
</s>
<s>
Among	O
the	O
challenges	O
in	O
tweeter	B-Device
design	O
and	O
manufacture	O
are	O
:	O
providing	O
adequate	O
damping	O
,	O
to	O
stop	O
the	O
dome	O
's	O
motion	O
rapidly	O
when	O
the	O
signal	O
ends	O
;	O
ensuring	O
suspension	O
linearity	O
,	O
allowing	O
high	O
output	O
at	O
the	O
low	O
end	O
of	O
its	O
frequency	O
range	O
;	O
ensuring	O
freedom	O
from	O
contact	O
with	O
the	O
magnet	O
assembly	O
,	O
keeping	O
the	O
dome	O
centered	O
as	O
it	O
moves	O
;	O
and	O
providing	O
adequate	O
power	O
handling	O
without	O
adding	O
excessive	O
mass	O
.	O
</s>
<s>
Tweeters	B-Device
can	O
also	O
work	O
in	O
collaboration	O
with	O
the	O
woofers	B-Device
that	O
are	O
responsible	O
for	O
generating	O
the	O
low	O
frequencies	O
or	O
bass	O
.	O
</s>
<s>
Some	O
tweeters	B-Device
sit	O
outside	O
the	O
main	O
enclosure	O
in	O
their	O
own	O
semi-independent	O
unit	O
.	O
</s>
<s>
Examples	O
include	O
"	O
super	B-Device
tweeters	I-Device
"	O
and	O
the	O
novel	O
"	O
egg	O
tweeter	B-Device
"	O
by	O
Ohm	O
.	O
</s>
<s>
The	O
separation	O
from	O
the	O
baffle	O
is	O
considered	O
to	O
be	O
optimal	O
under	O
the	O
theory	O
that	O
the	O
smallest	O
baffle	O
possible	O
is	O
optimal	O
for	O
tweeters	B-Device
.	O
</s>
<s>
Most	O
tweeters	B-Device
are	O
designed	O
to	O
reproduce	O
frequencies	O
up	O
to	O
the	O
formally	O
defined	O
upper	O
limit	O
of	O
the	O
human	O
hearing	O
range	O
(	O
typically	O
listed	O
as	O
20kHz	O
)	O
;	O
some	O
operate	O
at	O
frequencies	O
up	O
to	O
approximately	O
in	O
between	O
5kHz	O
to	O
20kHz	O
.	O
</s>
<s>
Tweeters	B-Device
with	O
a	O
greater	O
upper	O
range	O
have	O
been	O
designed	O
for	O
psychoacoustic	O
testing	O
,	O
for	O
extended-range	O
digital	O
audio	O
such	O
as	O
Super	O
Audio	O
CD	O
intended	O
for	O
audiophiles	O
,	O
for	O
biologists	O
performing	O
research	O
on	O
animal	O
response	O
to	O
sounds	O
,	O
and	O
for	O
ambient	O
sound	O
systems	O
in	O
zoos	O
.	O
</s>
<s>
Ribbon	O
tweeters	B-Device
have	O
been	O
made	O
that	O
can	O
reproduce	O
80kHz	O
and	O
even	O
100kHz	O
.	O
</s>
<s>
Celestion	O
were	O
the	O
first	O
manufacturers	O
to	O
fabricate	O
dome	O
tweeters	B-Device
out	O
of	O
a	O
metal	O
,	O
copper	O
.	O
</s>
<s>
In	O
general	O
,	O
smaller	O
dome	O
tweeters	B-Device
provide	O
wider	O
dispersion	O
of	O
sound	O
at	O
the	O
highest	O
frequencies	O
.	O
</s>
<s>
However	O
,	O
smaller	O
dome	O
tweeters	B-Device
have	O
less	O
radiating	O
area	O
,	O
which	O
limits	O
their	O
output	O
at	O
the	O
lower	O
end	O
of	O
their	O
range	O
;	O
and	O
they	O
have	O
smaller	O
voice	B-Device
coils	I-Device
,	O
which	O
limit	O
their	O
overall	O
power	O
output	O
.	O
</s>
<s>
A	O
wide	O
range	O
of	O
viscosity	B-Application
and	O
magnetic	O
density	O
variants	O
allow	O
designers	O
to	O
add	O
damping	O
,	O
cooling	O
,	O
or	O
both	O
.	O
</s>
<s>
Ferrofluid	O
also	O
aids	O
in	O
centering	O
the	O
voice	B-Device
coil	I-Device
in	O
the	O
magnetic	O
gap	O
,	O
reducing	O
distortion	O
.	O
</s>
<s>
If	O
a	O
tweeter	B-Device
has	O
been	O
subjected	O
to	O
elevated	O
power	O
levels	O
,	O
some	O
thickening	O
of	O
the	O
ferrofluid	O
occurs	O
,	O
as	O
a	O
portion	O
of	O
the	O
carrier	O
liquid	O
evaporates	O
.	O
</s>
<s>
In	O
extreme	O
cases	O
,	O
this	O
can	O
degrade	O
the	O
sound	O
quality	O
and	O
output	O
level	O
of	O
a	O
tweeter	B-Device
,	O
and	O
the	O
fluid	O
must	O
be	O
removed	O
and	O
new	O
fluid	O
installed	O
.	O
</s>
<s>
Tweeters	B-Device
designed	O
for	O
sound	O
reinforcement	O
and	O
musical	O
instrument	O
applications	O
are	O
broadly	O
similar	O
to	O
high	O
fidelity	O
tweeters	B-Device
,	O
though	O
they	O
're	O
usually	O
not	O
referred	O
to	O
as	O
tweeters	B-Device
,	O
but	O
as	O
"	O
high	O
frequency	O
drivers	O
"	O
.	O
</s>
<s>
Key	O
design	O
requirement	O
differences	O
are	O
:	O
mountings	O
built	O
for	O
repeated	O
shipping	O
and	O
handling	O
,	O
drivers	O
often	O
mounted	O
to	O
horn	B-Device
structures	O
to	O
provide	O
for	O
higher	O
sound	O
levels	O
and	O
greater	O
control	O
of	O
sound	O
dispersion	O
,	O
and	O
more	O
robust	O
voice	B-Device
coils	I-Device
to	O
withstand	O
the	O
higher	O
power	O
levels	O
typically	O
encountered	O
.	O
</s>
<s>
High	O
frequency	O
drivers	O
in	O
PA	O
horns	O
are	O
often	O
referred	O
to	O
as	O
"	O
compression	B-Device
drivers	I-Device
"	O
from	O
the	O
mode	O
of	O
acoustic	O
coupling	O
between	O
the	O
driver	O
diaphragm	O
and	O
the	O
horn	B-Device
throat	O
.	O
</s>
<s>
Various	O
materials	O
are	O
used	O
in	O
the	O
construction	O
of	O
compression	B-Device
driver	I-Device
diaphragms	O
including	O
titanium	O
,	O
aluminium	O
,	O
phenolic	O
impregnated	O
fabric	O
,	O
polyimide	O
and	O
PET	O
film	O
,	O
each	O
having	O
its	O
own	O
characteristics	O
.	O
</s>
<s>
The	O
diaphragm	O
is	O
glued	O
to	O
a	O
voice	B-Device
coil	I-Device
former	O
,	O
typically	O
made	O
from	O
a	O
different	O
material	O
from	O
the	O
dome	O
,	O
since	O
it	O
must	O
cope	O
with	O
heat	O
without	O
tearing	O
or	O
significant	O
dimensional	O
change	O
.	O
</s>
<s>
The	O
diaphragm	O
is	O
generally	O
shaped	O
like	O
an	O
inverted	O
dome	O
and	O
loads	O
into	O
a	O
series	O
of	O
tapered	O
channels	O
in	O
a	O
central	O
structure	O
called	O
a	O
phase	B-Architecture
plug	I-Architecture
,	O
which	O
equalizes	O
the	O
path	O
length	O
between	O
various	O
areas	O
of	O
the	O
diaphragm	O
and	O
the	O
horn	B-Device
throat	O
,	O
preventing	O
acoustic	O
cancellations	O
between	O
different	O
points	O
on	O
the	O
diaphragm	O
surface	O
.	O
</s>
<s>
The	O
phase	B-Architecture
plug	I-Architecture
exits	O
into	O
a	O
tapered	O
tube	O
,	O
which	O
forms	O
the	O
start	O
of	O
the	O
horn	B-Device
itself	O
.	O
</s>
<s>
This	O
slowly	O
expanding	O
throat	O
within	O
the	O
driver	O
is	O
continued	O
in	O
the	O
horn	B-Device
flare	O
.	O
</s>
<s>
The	O
horn	B-Device
flare	O
controls	O
the	O
coverage	O
pattern	O
,	O
or	O
directivity	O
,	O
and	O
as	O
an	O
acoustic	O
transformer	B-Algorithm
,	O
adds	O
gain	O
.	O
</s>
<s>
A	O
professional	O
horn	B-Device
and	O
compression	B-Device
driver	I-Device
combination	O
has	O
an	O
output	O
sensitivity	O
of	O
between	O
105	O
and	O
112dB/watt/meter	O
.	O
</s>
<s>
This	O
is	O
substantially	O
more	O
efficient	O
(	O
and	O
less	O
thermally	O
dangerous	O
to	O
a	O
small	O
voice	B-Device
coil	I-Device
and	O
former	O
)	O
than	O
other	O
tweeter	B-Device
construction	O
.	O
</s>
<s>
Cone	O
tweeters	B-Device
have	O
the	O
same	O
basic	O
design	O
and	O
form	O
as	O
a	O
woofer	B-Device
with	O
optimizations	O
to	O
operate	O
at	O
higher	O
frequencies	O
.	O
</s>
<s>
small	O
voice	B-Device
coils	I-Device
(	O
3/4	O
inch	O
is	O
typical	O
)	O
and	O
light	O
(	O
thin	O
)	O
wire	O
,	O
which	O
also	O
helps	O
the	O
tweeter	B-Device
cone	O
move	O
rapidly	O
.	O
</s>
<s>
Cone	O
tweeters	B-Device
were	O
popular	O
in	O
older	O
stereo	O
hi-fi	O
speakers	O
designed	O
and	O
manufactured	O
in	O
the	O
1960s	O
and	O
1970s	O
as	O
an	O
alternative	O
to	O
the	O
dome	O
tweeter	B-Device
(	O
which	O
was	O
developed	O
in	O
the	O
late	O
1950s	O
)	O
.	O
</s>
<s>
Cone	O
tweeters	B-Device
today	O
are	O
often	O
relatively	O
cheap	O
,	O
but	O
many	O
of	O
those	O
in	O
the	O
past	O
were	O
of	O
high	O
quality	O
,	O
such	O
as	O
those	O
made	O
by	O
Audax/Polydax	O
,	O
Bozak	O
,	O
CTS	O
,	O
JBL	O
,	O
Tonegen	O
and	O
SEAS	O
.	O
</s>
<s>
These	O
vintage	O
cone	O
tweeters	B-Device
exhibited	O
very	O
flat	O
frequency	O
response	O
,	O
low	O
distortion	O
,	O
fast	O
transient	O
response	O
,	O
a	O
low	O
resonance	O
frequency	O
and	O
a	O
gentle	O
low-end	O
roll-off	O
,	O
easing	O
crossover	B-Algorithm
design	O
.	O
</s>
<s>
Typical	O
of	O
the	O
1960s/1970s	O
-era	O
was	O
the	O
CTS	O
"	O
phenolic	O
ring	O
"	O
cone	O
tweeters	B-Device
,	O
exhibiting	O
flat	O
response	O
from	O
2,000	O
to	O
15,000	O
Hz	O
,	O
low	O
distortion	O
and	O
fast	O
transient	O
response	O
.	O
</s>
<s>
The	O
CTS	O
"	O
phenolic	O
ring	O
"	O
tweeter	B-Device
gets	O
its	O
name	O
from	O
the	O
orange-colored	O
edge	O
suspension	O
ring	O
that	O
it	O
has	O
which	O
is	O
made	O
from	O
phenolic	O
.	O
</s>
<s>
Cone	O
tweeters	B-Device
have	O
a	O
narrower	O
dispersion	O
characteristic	O
that	O
is	O
the	O
same	O
as	O
a	O
cone	O
woofer	B-Device
's	O
.	O
</s>
<s>
Many	O
designers	O
therefore	O
believed	O
this	O
made	O
them	O
a	O
good	O
match	O
to	O
cone	O
midranges	O
and	O
woofers	B-Device
,	O
allowing	O
for	O
superb	O
stereo	O
imaging	O
.	O
</s>
<s>
However	O
,	O
the	O
"	O
sweet	O
spot	O
"	O
created	O
by	O
the	O
narrow	O
dispersion	O
of	O
cone	O
tweeters	B-Device
is	O
small	O
.	O
</s>
<s>
Speakers	O
with	O
cone	O
tweeters	B-Device
offered	O
the	O
best	O
stereo	O
imaging	O
when	O
positioned	O
in	O
the	O
room	O
's	O
corners	O
,	O
a	O
common	O
practice	O
in	O
the	O
1950s	O
,	O
1960s	O
and	O
early	O
1970s	O
.	O
</s>
<s>
During	O
the	O
1970s	O
and	O
1980s	O
,	O
the	O
widespread	O
introduction	O
of	O
higher	O
quality	O
audiophile	O
discs	O
and	O
the	O
advent	O
of	O
the	O
CD	O
caused	O
the	O
cone	O
tweeter	B-Device
to	O
fall	O
out	O
of	O
popularity	O
because	O
cone	O
tweeters	B-Device
seldom	O
extend	O
past	O
15kHz	O
.	O
</s>
<s>
Audiophiles	O
felt	O
that	O
cone	O
tweeters	B-Device
lacked	O
the	O
"	O
airiness	O
"	O
of	O
dome	O
tweeters	B-Device
or	O
other	O
types	O
.	O
</s>
<s>
Nevertheless	O
,	O
many	O
high-end	O
cone	O
tweeters	B-Device
remained	O
in	O
limited	O
production	O
by	O
Audax	O
,	O
JBL	O
and	O
SEAS	O
until	O
the	O
mid-1980s	O
.	O
</s>
<s>
Cone	O
tweeters	B-Device
are	O
now	O
rarely	O
used	O
in	O
modern	O
hi-fi	O
usage	O
and	O
are	O
routinely	O
seen	O
in	O
low	O
cost	O
applications	O
such	O
as	O
factory	O
car	O
speakers	O
,	O
compact	O
stereo	O
systems	O
,	O
and	O
boom	O
boxes	O
.	O
</s>
<s>
Some	O
boutique	O
speaker	O
manufacturers	O
recently	O
have	O
returned	O
to	O
high-end	O
cone	O
tweeters	B-Device
,	O
especially	O
recreations	O
of	O
CTS	O
phenolic	O
ring	O
models	O
,	O
to	O
create	O
a	O
vintage-sounding	O
product	O
.	O
</s>
<s>
A	O
dome	O
tweeter	B-Device
is	O
constructed	O
by	O
attaching	O
a	O
voice	B-Device
coil	I-Device
to	O
a	O
dome	O
(	O
made	O
of	O
woven	O
fabric	O
,	O
thin	O
metal	O
or	O
other	O
suitable	O
material	O
)	O
,	O
which	O
is	O
attached	O
to	O
the	O
magnet	O
or	O
the	O
top	O
plate	O
via	O
a	O
low	O
compliance	O
suspension	O
.	O
</s>
<s>
These	O
tweeters	B-Device
typically	O
do	O
not	O
have	O
a	O
frame	O
or	O
basket	O
,	O
but	O
a	O
simple	O
front	O
plate	O
attached	O
to	O
the	O
magnet	O
assembly	O
.	O
</s>
<s>
Dome	O
tweeters	B-Device
are	O
categorized	O
by	O
their	O
voice	B-Device
coil	I-Device
diameter	O
,	O
and	O
range	O
from	O
19mm	O
(	O
0.75in	O
)	O
,	O
through	O
38mm	O
(	O
1.5in	O
)	O
.	O
</s>
<s>
The	O
overwhelming	O
majority	O
of	O
dome	O
tweeters	B-Device
presently	O
used	O
in	O
hi-fi	O
speakers	O
are	O
25mm	O
(	O
1in	O
)	O
in	O
diameter	O
.	O
</s>
<s>
These	O
tweeters	B-Device
have	O
different	O
directivity	O
characteristics	O
when	O
compared	O
to	O
standard	O
dome	O
tweeters	B-Device
.	O
</s>
<s>
A	O
piezo	O
(	O
or	O
piezo-electric	O
)	O
tweeter	B-Device
contains	O
a	O
piezoelectric	O
crystal	O
coupled	O
to	O
a	O
mechanical	O
diaphragm	O
.	O
</s>
<s>
In	O
addition	O
,	O
a	O
permanently	O
polarized	O
material	O
such	O
as	O
quartz	B-General_Concept
(	O
SiO2	O
)	O
or	O
barium	O
titanate	O
(	O
BaTiO3	O
)	O
will	O
produce	O
an	O
electric	O
field	O
when	O
the	O
material	O
changes	O
dimensions	O
as	O
a	O
result	O
of	O
an	O
imposed	O
mechanical	O
force	O
.	O
</s>
<s>
Piezo	O
tweeters	B-Device
rarely	O
get	O
used	O
in	O
high-end	O
audio	O
because	O
of	O
their	O
low	O
fidelity	O
,	O
although	O
they	O
did	O
feature	O
in	O
some	O
high-end	O
designs	O
of	O
the	O
late	O
‘	O
70s	O
,	O
such	O
as	O
the	O
Celef	O
PE1	O
in	O
which	O
they	O
were	O
utilised	O
as	O
a	O
super	B-Device
tweeter	I-Device
in	O
combination	O
with	O
a	O
conventional	O
dome	O
tweeter	B-Device
.	O
</s>
<s>
They	O
are	O
often	O
used	O
in	O
toys	O
,	O
buzzers	O
,	O
alarms	O
,	O
bass	O
guitar	O
speaker	B-Device
cabinets	I-Device
,	O
cheap	O
computer	O
or	O
stereo	O
speakers	O
and	O
PA	O
horns	O
.	O
</s>
<s>
A	O
ribbon	O
tweeter	B-Device
uses	O
a	O
very	O
thin	O
diaphragm	O
(	O
often	O
of	O
aluminum	O
,	O
or	O
perhaps	O
metalized	O
plastic	O
film	O
)	O
that	O
supports	O
a	O
planar	O
coil	O
frequently	O
made	O
by	O
deposition	O
of	O
aluminium	O
vapor	O
,	O
suspended	O
in	O
a	O
powerful	O
magnetic	O
field	O
(	O
typically	O
provided	O
by	O
neodymium	O
magnets	O
)	O
to	O
reproduce	O
high	O
frequencies	O
.	O
</s>
<s>
The	O
development	O
of	O
ribbon	O
tweeters	B-Device
has	O
more	O
or	O
less	O
followed	O
the	O
development	O
of	O
ribbon	B-Algorithm
microphones	I-Algorithm
.	O
</s>
<s>
But	O
higher	O
power	O
versions	O
of	O
ribbon	O
tweeters	B-Device
are	O
becoming	O
common	O
in	O
large-scale	O
sound	O
reinforcement	O
line	O
array	O
systems	O
,	O
which	O
can	O
serve	O
audiences	O
of	O
thousands	O
.	O
</s>
<s>
They	O
are	O
attractive	O
in	O
these	O
applications	O
since	O
nearly	O
all	O
ribbon	O
tweeters	B-Device
inherently	O
exhibit	O
useful	O
directional	O
properties	O
,	O
with	O
very	O
wide	O
horizontal	O
dispersion	O
(	O
coverage	O
)	O
and	O
very	O
tight	O
vertical	O
dispersion	O
.	O
</s>
<s>
These	O
drivers	O
can	O
easily	O
be	O
stacked	O
vertically	O
,	O
building	O
a	O
high	O
frequency	O
line	O
array	O
that	O
produces	O
high	O
sound	O
pressure	O
levels	O
much	O
farther	O
away	O
from	O
the	O
speaker	O
locations	O
than	O
do	O
conventional	O
tweeters	B-Device
.	O
</s>
<s>
Some	O
loudspeaker	O
designers	O
use	O
a	O
planar-magnetic	O
tweeter	B-Device
,	O
sometimes	O
called	O
a	O
quasi-ribbon	O
.	O
</s>
<s>
Planar	O
magnetic	O
tweeters	B-Device
are	O
generally	O
less	O
expensive	O
than	O
true	O
ribbon	O
tweeters	B-Device
,	O
but	O
are	O
not	O
precisely	O
equivalent	O
as	O
a	O
metal	O
foil	O
ribbon	O
is	O
lighter	O
than	O
the	O
diaphragm	O
in	O
a	O
planar	O
magnetic	O
tweeter	B-Device
and	O
the	O
magnetic	O
structures	O
are	O
different	O
.	O
</s>
<s>
Usually	O
a	O
thin	O
piece	O
of	O
PET	O
film	O
or	O
plastic	O
with	O
a	O
voice	B-Device
coil	I-Device
wire	O
running	O
numerous	O
times	O
vertically	O
on	O
the	O
material	O
is	O
used	O
.	O
</s>
<s>
The	O
magnet	O
structure	O
is	O
less	O
expensive	O
than	O
for	O
ribbon	O
tweeters	B-Device
.	O
</s>
<s>
An	O
electrostatic	B-Device
tweeter	I-Device
operates	O
on	O
the	O
same	O
principles	O
as	O
a	O
full-range	B-Device
electrostatic	B-Device
speaker	I-Device
or	O
a	O
pair	O
of	O
electrostatic	O
headphones	O
.	O
</s>
<s>
The	O
output	O
of	O
the	O
driving	O
amplifier	O
is	O
applied	O
to	O
the	O
primary	O
of	O
a	O
step-up	O
transformer	B-Algorithm
with	O
a	O
center-tapped	O
secondary	O
,	O
and	O
a	O
very	O
high	O
voltage	O
—	O
several	O
hundred	O
to	O
several	O
thousand	O
volts	O
—	O
is	O
applied	O
between	O
the	O
center	O
tap	O
of	O
the	O
transformer	B-Algorithm
and	O
the	O
diaphragm	O
.	O
</s>
<s>
The	O
stators	O
are	O
connected	O
to	O
the	O
remaining	O
terminals	O
of	O
the	O
transformer	B-Algorithm
.	O
</s>
<s>
When	O
an	O
audio	O
signal	O
is	O
applied	O
to	O
the	O
primary	O
of	O
the	O
transformer	B-Algorithm
,	O
the	O
stators	O
are	O
electrically	O
driven	O
180	O
degrees	O
out	O
of	O
phase	O
,	O
alternately	O
attracting	O
and	O
repelling	O
the	O
diaphragm	O
.	O
</s>
<s>
An	O
uncommon	O
way	O
of	O
driving	O
an	O
electrostatic	B-Device
speaker	I-Device
without	O
a	O
transformer	B-Algorithm
is	O
to	O
connect	O
the	O
plates	O
of	O
a	O
push-pull	O
vacuum	O
tube	O
amplifier	O
directly	O
to	O
the	O
stators	O
,	O
and	O
the	O
high	O
voltage	O
supply	O
between	O
the	O
diaphragm	O
and	O
ground	O
.	O
</s>
<s>
The	O
Air	B-Device
Motion	I-Device
Transformer	I-Device
tweeter	B-Device
works	O
by	O
pushing	O
air	O
out	O
perpendicularly	O
from	O
the	O
pleated	O
diaphragm	O
.	O
</s>
<s>
In	O
past	O
decades	O
,	O
ESS	O
of	O
California	O
produced	O
a	O
series	O
of	O
hybrid	O
loudspeakers	O
using	O
such	O
tweeters	B-Device
,	O
along	O
with	O
conventional	O
woofers	B-Device
,	O
referring	O
to	O
them	O
as	O
Heil	O
transducers	O
after	O
their	O
inventor	O
,	O
Oskar	O
Heil	O
.	O
</s>
<s>
A	O
horn	B-Device
tweeter	B-Device
is	O
any	O
of	O
the	O
above	O
tweeters	B-Device
coupled	O
to	O
a	O
flared	O
or	O
horn	B-Device
structure	O
.	O
</s>
<s>
Horns	O
are	O
used	O
for	O
two	O
purposes	O
—	O
to	O
control	O
dispersion	O
,	O
and	O
to	O
couple	O
the	O
tweeter	B-Device
diaphragm	O
to	O
the	O
air	O
for	O
higher	O
efficiency	O
.	O
</s>
<s>
The	O
tweeter	B-Device
in	O
either	O
case	O
is	O
usually	O
termed	O
a	O
compression	B-Device
driver	I-Device
and	O
is	O
quite	O
different	O
from	O
more	O
common	O
types	O
of	O
tweeters	B-Device
(	O
see	O
above	O
)	O
.	O
</s>
<s>
Properly	O
used	O
,	O
a	O
horn	B-Device
improves	O
the	O
off-axis	O
response	O
of	O
the	O
tweeter	B-Device
by	O
controlling	O
(	O
i.e.	O
,	O
reducing	O
)	O
the	O
directivity	O
of	O
the	O
tweeter	B-Device
.	O
</s>
<s>
It	O
can	O
also	O
improve	O
the	O
efficiency	O
of	O
the	O
tweeter	B-Device
by	O
coupling	O
the	O
relatively	O
high	O
acoustic	O
impedance	O
of	O
the	O
driver	O
to	O
the	O
lower	O
impedance	O
of	O
the	O
air	O
.	O
</s>
<s>
The	O
larger	O
the	O
horn	B-Device
,	O
the	O
lower	O
the	O
frequencies	O
at	O
which	O
it	O
can	O
work	O
,	O
since	O
large	O
horns	O
provide	O
coupling	O
to	O
the	O
air	O
at	O
lower	O
frequencies	O
.	O
</s>
<s>
Horn	B-Device
tweeters	B-Device
may	O
have	O
a	O
somewhat	O
'	O
different	O
 '	O
sonic	O
signature	O
than	O
simple	O
dome	O
tweeters	B-Device
.	O
</s>
<s>
Perhaps	O
concerned	O
about	O
the	O
image	O
of	O
poorly	O
designed	O
horns	O
,	O
some	O
manufacturers	O
use	O
horn	B-Device
loaded	O
tweeters	B-Device
,	O
but	O
avoid	O
using	O
the	O
term	O
.	O
</s>
<s>
Their	O
euphemisms	O
include	O
"	O
elliptical	O
aperture	O
"	O
"	O
Semi-horn	O
"	O
and	O
"	O
Directivity	O
controlled	O
"	O
.	O
</s>
<s>
These	O
are	O
,	O
nonetheless	O
,	O
a	O
form	O
of	O
horn	B-Device
loading	I-Device
.	O
</s>
<s>
Because	O
ionized	O
gas	O
is	O
electrically	O
charged	O
and	O
so	O
can	O
be	O
manipulated	O
by	O
a	O
variable	O
electrical	O
field	O
,	O
it	O
is	O
possible	O
to	O
use	O
a	O
small	O
sphere	O
of	O
plasma	O
as	O
a	O
tweeter	B-Device
.	O
</s>
<s>
Such	O
tweeters	B-Device
are	O
called	O
a	O
plasma	O
tweeter	B-Device
or	O
ion	O
tweeter	B-Device
.	O
</s>
<s>
They	O
can	O
be	O
more	O
complex	O
than	O
other	O
tweeters	B-Device
(	O
plasma	O
generation	O
is	O
not	O
required	O
in	O
other	O
types	O
)	O
,	O
but	O
offer	O
the	O
advantage	O
that	O
the	O
moving	O
mass	O
is	O
optimally	O
low	O
-	O
if	O
not	O
relatively	O
massless	O
and	O
so	O
very	O
responsive	O
to	O
the	O
signal	O
input	O
.	O
</s>
<s>
The	O
early	O
models	O
of	O
these	O
tweeters	B-Device
were	O
not	O
capable	O
of	O
high	O
output	O
,	O
nor	O
of	O
other	O
than	O
very	O
high	O
frequency	O
reproduction	O
,	O
and	O
so	O
are	O
usually	O
used	O
at	O
the	O
throat	O
of	O
a	O
horn	B-Device
structure	O
to	O
manage	O
usable	O
output	O
levels	O
.	O
</s>
<s>
One	O
disadvantage	O
is	O
that	O
the	O
plasma	O
arc	O
can	O
produce	O
ozone	O
and	O
NOx	B-Application
,	O
poison	O
gases	O
,	O
in	O
small	O
quantities	O
as	O
a	O
by-product	O
.	O
</s>
<s>
In	O
the	O
past	O
,	O
the	O
dominant	O
manufacturer	O
in	O
the	O
US	O
was	O
DuKane	O
near	O
St	O
Louis	O
,	O
who	O
made	O
the	O
Ionovac	O
;	O
also	O
sold	O
in	O
a	O
UK	O
variant	O
as	O
the	O
Ionophone	B-Device
.	O
</s>
<s>
These	O
early	O
models	O
were	O
finicky	O
and	O
required	O
regular	O
replacement	O
of	O
the	O
cell	O
in	O
which	O
the	O
plasma	O
was	O
generated	O
(	O
the	O
DuKane	O
unit	O
used	O
a	O
precision	O
machined	O
quartz	B-General_Concept
cell	O
)	O
.	O
</s>
<s>
In	O
the	O
1980s	O
,	O
the	O
Plasmatronics	O
speaker	O
also	O
used	O
a	O
plasma	O
tweeter	B-Device
,	O
though	O
the	O
manufacturer	O
did	O
not	O
stay	O
in	O
business	O
very	O
long	O
and	O
very	O
few	O
of	O
these	O
complex	O
units	O
were	O
sold	O
.	O
</s>
