<s>
Audio	B-Algorithm
crossovers	I-Algorithm
are	O
a	O
type	O
of	O
electronic	B-Architecture
filter	I-Architecture
circuitry	O
that	O
splits	O
an	O
audio	O
signal	O
into	O
two	O
or	O
more	O
frequency	O
ranges	O
,	O
so	O
that	O
the	O
signals	O
can	O
be	O
sent	O
to	O
loudspeaker	B-Device
drivers	I-Device
that	O
are	O
designed	O
to	O
operate	O
within	O
different	O
frequency	O
ranges	O
.	O
</s>
<s>
The	O
crossover	B-Algorithm
filters	I-Algorithm
can	O
be	O
either	O
active	O
or	O
passive	O
.	O
</s>
<s>
They	O
are	O
often	O
described	O
as	O
two-way	O
or	O
three-way	O
,	O
which	O
indicate	O
,	O
respectively	O
,	O
that	O
the	O
crossover	B-Algorithm
splits	O
a	O
given	O
signal	O
into	O
two	O
frequency	O
ranges	O
or	O
three	O
frequency	O
ranges	O
.	O
</s>
<s>
Crossovers	B-Algorithm
are	O
used	O
in	O
loudspeaker	B-Device
cabinets	I-Device
,	O
power	O
amplifiers	O
in	O
consumer	O
electronics	O
(	O
hi-fi	O
,	O
home	O
cinema	O
sound	O
and	O
car	O
audio	O
)	O
and	O
pro	O
audio	O
and	O
musical	O
instrument	O
amplifier	O
products	O
.	O
</s>
<s>
For	O
the	O
latter	O
two	O
markets	O
,	O
crossovers	B-Algorithm
are	O
used	O
in	O
bass	O
amplifiers	O
,	O
keyboard	O
amplifiers	O
,	O
bass	O
and	O
keyboard	O
speaker	B-Device
enclosures	I-Device
and	O
sound	O
reinforcement	O
system	O
equipment	O
(	O
PA	O
speakers	O
,	O
monitor	O
speakers	O
,	O
subwoofer	B-Application
systems	O
,	O
etc	O
.	O
</s>
<s>
Crossovers	B-Algorithm
are	O
used	O
because	O
most	O
individual	O
loudspeaker	B-Device
drivers	I-Device
are	O
incapable	O
of	O
covering	O
the	O
entire	O
audio	O
spectrum	O
from	O
low	O
frequencies	O
to	O
high	O
frequencies	O
with	O
acceptable	O
relative	O
volume	O
and	O
absence	O
of	O
distortion	O
.	O
</s>
<s>
Most	O
hi-fi	O
speaker	O
systems	O
and	O
sound	O
reinforcement	O
system	O
speaker	B-Device
cabinets	I-Device
use	O
a	O
combination	O
of	O
multiple	O
loudspeaker	B-Device
drivers	I-Device
,	O
each	O
catering	O
to	O
a	O
different	O
frequency	B-Algorithm
band	I-Algorithm
.	O
</s>
<s>
A	O
standard	O
simple	O
example	O
is	O
in	O
hi-fi	O
and	O
PA	O
system	O
cabinets	B-Device
that	O
contain	O
a	O
woofer	B-Device
for	O
low	O
and	O
mid	O
frequencies	O
and	O
a	O
tweeter	B-Device
for	O
high	O
frequencies	O
.	O
</s>
<s>
Since	O
a	O
sound	O
signal	O
source	O
,	O
be	O
it	O
recorded	O
music	O
from	O
a	O
CD	B-Device
player	I-Device
or	O
a	O
live	O
band	O
's	O
mix	O
from	O
an	O
audio	O
console	O
,	O
has	O
all	O
of	O
the	O
low	O
,	O
mid	O
and	O
high	O
frequencies	O
combined	O
,	O
a	O
crossover	B-Algorithm
circuit	O
is	O
used	O
to	O
split	O
the	O
audio	O
signal	O
into	O
separate	O
frequency	B-Algorithm
bands	I-Algorithm
that	O
can	O
be	O
separately	O
routed	O
to	O
loudspeakers	O
,	O
tweeters	B-Device
or	O
horns	O
optimized	O
for	O
those	O
frequency	B-Algorithm
bands	I-Algorithm
.	O
</s>
<s>
Passive	O
crossovers	B-Algorithm
are	O
probably	O
the	O
most	O
common	O
type	O
of	O
audio	B-Algorithm
crossover	I-Algorithm
.	O
</s>
<s>
They	O
use	O
a	O
network	O
of	O
passive	O
electrical	O
components	O
(	O
e.g.	O
,	O
capacitors	O
,	O
inductors	O
and	O
resistors	O
)	O
to	O
split	O
up	O
an	O
amplified	O
signal	O
coming	O
from	O
one	O
power	O
amplifier	O
so	O
that	O
it	O
can	O
be	O
sent	O
to	O
two	O
or	O
more	O
loudspeaker	B-Device
drivers	I-Device
(	O
e.g.	O
,	O
a	O
woofer	B-Device
and	O
a	O
very	O
low	O
frequency	O
subwoofer	B-Application
,	O
or	O
a	O
woofer	B-Device
and	O
a	O
tweeter	B-Device
,	O
or	O
a	O
woofer-midrange-tweeter	O
combination	O
)	O
.	O
</s>
<s>
Active	B-Algorithm
crossovers	I-Algorithm
are	O
distinguished	O
from	O
passive	O
crossovers	B-Algorithm
in	O
that	O
they	O
split	O
up	O
an	O
audio	O
signal	O
prior	O
to	O
the	O
power	O
amplification	O
stage	O
so	O
that	O
it	O
can	O
be	O
sent	O
to	O
two	O
or	O
more	O
power	O
amplifiers	O
,	O
each	O
of	O
which	O
is	O
connected	O
to	O
a	O
separate	O
loudspeaker	B-Device
driver	I-Device
.	O
</s>
<s>
Home	O
cinema	O
5.1	O
surround	O
sound	O
audio	O
systems	O
use	O
a	O
crossover	B-Algorithm
that	O
separates	O
out	O
the	O
very-low	O
frequency	O
signal	O
,	O
so	O
that	O
it	O
can	O
be	O
sent	O
to	O
a	O
subwoofer	B-Application
,	O
and	O
then	O
sending	O
the	O
remaining	O
low-	O
,	O
mid	O
-	O
and	O
high-range	O
frequencies	O
to	O
five	O
speakers	O
which	O
are	O
placed	O
around	O
the	O
listener	O
.	O
</s>
<s>
In	O
a	O
typical	O
application	O
,	O
the	O
signals	O
sent	O
to	O
the	O
surround	O
speaker	B-Device
cabinets	I-Device
are	O
further	O
split	O
up	O
using	O
a	O
passive	O
crossover	B-Algorithm
into	O
a	O
low/mid	O
-range	O
woofer	B-Device
and	O
a	O
high-range	O
tweeter	B-Device
.	O
</s>
<s>
Active	B-Algorithm
crossovers	I-Algorithm
come	O
in	O
both	O
digital	B-General_Concept
and	O
analog	O
varieties	O
.	O
</s>
<s>
Digital	B-General_Concept
active	B-Algorithm
crossovers	I-Algorithm
often	O
include	O
additional	O
signal	O
processing	O
,	O
such	O
as	O
limiting	O
,	O
delay	O
,	O
and	O
equalization	O
.	O
</s>
<s>
Signal	O
crossovers	B-Algorithm
allow	O
the	O
audio	O
signal	O
to	O
be	O
split	O
into	O
bands	O
that	O
are	O
processed	O
separately	O
before	O
they	O
are	O
mixed	O
together	O
again	O
.	O
</s>
<s>
Some	O
examples	O
are	O
multiband	O
compression	O
,	O
limiting	O
,	O
de-essing	B-Application
,	O
multiband	O
distortion	O
,	O
bass	O
enhancement	O
,	O
high	O
frequency	O
exciters	O
,	O
and	O
noise	O
reduction	O
such	O
as	O
Dolby	O
A	O
noise	O
reduction	O
.	O
</s>
<s>
The	O
definition	O
of	O
an	O
ideal	O
audio	B-Algorithm
crossover	I-Algorithm
changes	O
relative	O
to	O
the	O
task	O
and	O
audio	O
application	O
at	O
hand	O
.	O
</s>
<s>
If	O
the	O
separate	O
bands	O
are	O
to	O
be	O
mixed	O
back	O
together	O
again	O
(	O
as	O
in	O
multiband	O
processing	O
)	O
,	O
then	O
the	O
ideal	O
audio	B-Algorithm
crossover	I-Algorithm
would	O
split	O
the	O
incoming	O
audio	O
signal	O
into	O
separate	O
bands	O
that	O
do	O
not	O
overlap	O
or	O
interact	O
and	O
which	O
result	O
in	O
an	O
output	O
signal	O
unchanged	O
in	O
frequency	O
,	O
relative	O
levels	O
,	O
and	O
phase	O
response	O
.	O
</s>
<s>
On	O
the	O
other	O
hand	O
,	O
if	O
the	O
audio	B-Algorithm
crossover	I-Algorithm
separates	O
the	O
audio	O
bands	O
in	O
a	O
loudspeaker	O
,	O
there	O
is	O
no	O
requirement	O
for	O
mathematically	O
ideal	O
characteristics	O
within	O
the	O
crossover	B-Algorithm
itself	O
,	O
as	O
the	O
frequency	O
and	O
phase	O
response	O
of	O
the	O
loudspeaker	B-Device
drivers	I-Device
within	O
their	O
mountings	O
will	O
eclipse	O
the	O
results	O
.	O
</s>
<s>
Satisfactory	O
output	O
of	O
the	O
complete	O
system	O
comprising	O
the	O
audio	B-Algorithm
crossover	I-Algorithm
and	O
the	O
loudspeaker	B-Device
drivers	I-Device
in	O
their	O
enclosure(s )	O
is	O
the	O
design	O
goal	O
.	O
</s>
<s>
Such	O
a	O
goal	O
is	O
often	O
achieved	O
using	O
non-ideal	O
,	O
asymmetric	O
crossover	B-Algorithm
filter	I-Algorithm
characteristics	O
.	O
</s>
<s>
Many	O
different	O
crossover	B-Algorithm
types	O
are	O
used	O
in	O
audio	O
,	O
but	O
they	O
generally	O
belong	O
to	O
one	O
of	O
the	O
following	O
classes	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
loudspeaker	O
with	O
a	O
woofer	B-Device
and	O
a	O
tweeter	B-Device
is	O
a	O
2-way	O
loudspeaker	O
system	O
.	O
</s>
<s>
An	O
N-way	O
loudspeaker	O
usually	O
has	O
an	O
N-way	O
crossover	B-Algorithm
to	O
divide	O
the	O
signal	O
among	O
the	O
drivers	O
.	O
</s>
<s>
A	O
2-way	O
crossover	B-Algorithm
consists	O
of	O
a	O
low-pass	B-Algorithm
and	O
a	O
high-pass	O
filter	O
.	O
</s>
<s>
A	O
3-way	O
crossover	B-Algorithm
is	O
constructed	O
as	O
a	O
combination	O
of	O
low-pass	B-Algorithm
,	O
band-pass	O
and	O
high-pass	O
filters	O
(	O
LPF	O
,	O
BPF	O
and	O
HPF	O
respectively	O
)	O
.	O
</s>
<s>
4	O
(	O
or	O
more	O
)	O
way	O
crossovers	B-Algorithm
are	O
not	O
very	O
common	O
in	O
speaker	O
design	O
,	O
primarily	O
due	O
to	O
the	O
complexity	O
involved	O
,	O
which	O
is	O
not	O
generally	O
justified	O
by	O
better	O
acoustic	O
performance	O
.	O
</s>
<s>
An	O
extra	O
HPF	O
section	O
may	O
be	O
present	O
in	O
an	O
"	O
N-way	O
"	O
loudspeaker	O
crossover	B-Algorithm
to	O
protect	O
the	O
lowest-frequency	O
driver	O
from	O
frequencies	O
lower	O
than	O
it	O
can	O
safely	O
handle	O
.	O
</s>
<s>
Such	O
a	O
crossover	B-Algorithm
would	O
then	O
have	O
a	O
bandpass	O
filter	O
for	O
the	O
lowest-frequency	O
driver	O
.	O
</s>
<s>
Recently	O
,	O
a	O
number	O
of	O
manufacturers	O
have	O
begun	O
using	O
what	O
is	O
often	O
called	O
"	O
N.5-way	O
"	O
crossover	B-Algorithm
techniques	O
for	O
stereo	O
loudspeaker	O
crossovers	B-Algorithm
.	O
</s>
<s>
This	O
usually	O
indicates	O
the	O
addition	O
of	O
a	O
second	O
woofer	B-Device
that	O
plays	O
the	O
same	O
bass	O
range	O
as	O
the	O
main	O
woofer	B-Device
but	O
rolls	O
off	O
far	O
before	O
the	O
main	O
woofer	B-Device
does	O
.	O
</s>
<s>
Crossovers	B-Algorithm
can	O
also	O
be	O
classified	O
based	O
on	O
the	O
type	O
of	O
components	O
used	O
.	O
</s>
<s>
A	O
passive	O
crossover	B-Algorithm
splits	O
up	O
an	O
audio	O
signal	O
after	O
it	O
is	O
amplified	O
by	O
a	O
single	O
power	O
amplifier	O
,	O
so	O
that	O
the	O
amplified	O
signal	O
can	O
be	O
sent	O
to	O
two	O
or	O
more	O
driver	O
types	O
,	O
each	O
of	O
which	O
cover	O
different	O
frequency	O
ranges	O
.	O
</s>
<s>
These	O
crossover	B-Algorithm
are	O
made	O
entirely	O
of	O
passive	O
components	O
and	O
circuitry	O
;	O
the	O
term	O
"	O
passive	O
"	O
means	O
that	O
no	O
additional	O
power	O
source	O
is	O
needed	O
for	O
the	O
circuitry	O
.	O
</s>
<s>
A	O
passive	O
crossover	B-Algorithm
just	O
needs	O
to	O
be	O
connected	O
by	O
wiring	O
to	O
the	O
power	O
amplifier	O
signal	O
.	O
</s>
<s>
Passive	O
crossovers	B-Algorithm
are	O
usually	O
arranged	O
in	O
a	O
Cauer	O
topology	O
to	O
achieve	O
a	O
Butterworth	O
filter	O
effect	O
.	O
</s>
<s>
Very	O
high-performance	O
passive	O
crossovers	B-Algorithm
are	O
likely	O
to	O
be	O
more	O
expensive	O
than	O
active	B-Algorithm
crossovers	I-Algorithm
since	O
individual	O
components	O
capable	O
of	O
good	O
performance	O
at	O
the	O
high	O
currents	O
and	O
voltages	O
at	O
which	O
speaker	O
systems	O
are	O
driven	O
are	O
hard	O
to	O
make	O
.	O
</s>
<s>
Inexpensive	O
consumer	O
electronics	O
products	O
,	O
such	O
as	O
budget-priced	O
Home	O
theater	O
in	O
a	O
box	O
packages	O
and	O
low-cost	O
boom	O
boxes	O
,	O
use	O
lower	O
quality	O
passive	O
crossovers	B-Algorithm
,	O
often	O
utilizing	O
lower-order	O
filter	O
networks	O
with	O
fewer	O
components	O
.	O
</s>
<s>
Expensive	O
hi-fi	O
speaker	O
systems	O
and	O
receivers	O
use	O
higher	O
quality	O
passive	O
crossovers	B-Algorithm
,	O
to	O
obtain	O
improved	O
sound	O
quality	O
and	O
lower	O
distortion	O
.	O
</s>
<s>
The	O
same	O
price/quality	O
approach	O
is	O
used	O
with	O
sound	O
reinforcement	O
system	O
equipment	O
and	O
musical	O
instrument	O
amplifiers	O
and	O
speaker	B-Device
cabinets	I-Device
;	O
a	O
low-priced	O
stage	O
monitor	O
,	O
PA	O
speaker	O
or	O
bass	O
amplifier	O
speaker	B-Device
cabinet	I-Device
will	O
typically	O
use	O
lower	O
quality	O
,	O
lower	O
priced	O
passive	O
crossovers	B-Algorithm
,	O
whereas	O
high-priced	O
,	O
high-quality	O
cabinets	B-Device
will	O
use	O
better	O
quality	O
crossovers	B-Algorithm
.	O
</s>
<s>
Passive	O
crossovers	B-Algorithm
may	O
use	O
capacitors	O
made	O
from	O
polypropylene	O
,	O
metalized	O
polyester	O
foil	O
,	O
paper	O
and	O
electrolytic	O
capacitors	O
technology	O
.	O
</s>
<s>
Some	O
passive	O
networks	O
include	O
devices	O
such	O
as	O
fuses	O
,	O
PTC	O
devices	O
,	O
bulbs	O
or	O
circuit	O
breakers	O
to	O
protect	O
the	O
loudspeaker	B-Device
drivers	I-Device
from	O
accidental	O
overpowering	O
(	O
e.g.	O
,	O
from	O
sudden	O
surges	O
or	O
spikes	O
)	O
.	O
</s>
<s>
Modern	O
passive	O
crossovers	B-Algorithm
increasingly	O
incorporate	O
equalization	O
networks	O
(	O
e.g.	O
,	O
Zobel	O
networks	O
)	O
that	O
compensate	O
for	O
the	O
changes	O
in	O
impedance	O
with	O
frequency	O
inherent	O
in	O
virtually	O
all	O
loudspeakers	O
.	O
</s>
<s>
Ideal	O
crossover	B-Algorithm
filters	I-Algorithm
,	O
including	O
impedance	O
compensation	O
and	O
equalization	O
networks	O
,	O
can	O
be	O
very	O
difficult	O
to	O
design	O
,	O
as	O
the	O
components	O
interact	O
in	O
complex	O
ways	O
.	O
</s>
<s>
Crossover	B-Algorithm
design	O
expert	O
Siegfried	O
Linkwitz	O
said	O
of	O
them	O
that	O
"	O
the	O
only	O
excuse	O
for	O
passive	O
crossovers	B-Algorithm
is	O
their	O
low	O
cost	O
.	O
</s>
<s>
This	O
implementation	O
is	O
called	O
a	O
passive	O
line-level	O
crossover	B-Algorithm
.	O
</s>
<s>
An	O
active	B-Algorithm
crossover	I-Algorithm
contains	O
active	O
components	O
in	O
its	O
filters	O
,	O
such	O
as	O
transistors	O
and	O
operational	O
amplifiers	O
.	O
</s>
<s>
In	O
contrast	O
to	O
passive	O
crossovers	B-Algorithm
,	O
which	O
operate	O
after	O
the	O
power	O
amplifier	O
's	O
output	O
at	O
high	O
current	O
and	O
in	O
some	O
cases	O
high	O
voltage	O
,	O
active	B-Algorithm
crossovers	I-Algorithm
are	O
operated	O
at	O
levels	O
that	O
are	O
suited	O
to	O
power	O
amplifier	O
inputs	O
.	O
</s>
<s>
Active	B-Algorithm
crossovers	I-Algorithm
always	O
require	O
the	O
use	O
of	O
power	O
amplifiers	O
for	O
each	O
output	O
band	O
.	O
</s>
<s>
Thus	O
a	O
2-way	O
active	B-Algorithm
crossover	I-Algorithm
needs	O
two	O
amplifiers	O
—	O
one	O
for	O
the	O
woofer	B-Device
and	O
one	O
for	O
the	O
tweeter	B-Device
.	O
</s>
<s>
This	O
means	O
that	O
a	O
loudspeaker	O
system	O
that	O
is	O
based	O
on	O
active	B-Algorithm
crossovers	I-Algorithm
will	O
often	O
cost	O
more	O
than	O
a	O
passive-crossover-based	O
system	O
.	O
</s>
<s>
Despite	O
the	O
cost	O
and	O
complication	O
disadvantages	O
,	O
active	B-Algorithm
crossovers	I-Algorithm
provide	O
the	O
following	O
advantages	O
over	O
passive	O
ones	O
:	O
</s>
<s>
typically	O
,	O
the	O
possibility	O
of	O
an	O
easy	O
way	O
to	O
vary	O
or	O
fine-tune	O
each	O
frequency	B-Algorithm
band	I-Algorithm
to	O
the	O
specific	O
drivers	O
used	O
.	O
</s>
<s>
Examples	O
would	O
be	O
crossover	B-Algorithm
slope	O
,	O
filter	O
type	O
(	O
e.g.	O
,	O
Bessel	O
,	O
Butterworth	O
,	O
Linkwitz-Riley	O
,	O
etc	O
.	O
</s>
<s>
Active	B-Algorithm
crossovers	I-Algorithm
can	O
be	O
implemented	O
digitally	O
using	O
a	O
digital	B-Architecture
signal	I-Architecture
processor	I-Architecture
or	O
other	O
microprocessor	B-Architecture
.	O
</s>
<s>
They	O
either	O
use	O
digital	B-General_Concept
approximations	O
to	O
traditional	O
analog	O
circuits	O
,	O
known	O
as	O
IIR	O
filters	O
(	O
Bessel	O
,	O
Butterworth	O
,	O
Linkwitz-Riley	O
etc	O
.	O
</s>
<s>
This	O
crossover	B-Algorithm
type	O
is	O
mechanical	O
and	O
uses	O
the	O
properties	O
of	O
the	O
materials	O
in	O
a	O
driver	O
diaphragm	O
to	O
achieve	O
the	O
necessary	O
filtering	O
.	O
</s>
<s>
Such	O
crossovers	B-Algorithm
are	O
commonly	O
found	O
in	O
full-range	B-Device
speakers	I-Device
which	O
are	O
designed	O
to	O
cover	O
as	O
much	O
of	O
the	O
audio	O
band	O
as	O
possible	O
.	O
</s>
<s>
One	O
such	O
is	O
constructed	O
by	O
coupling	O
the	O
cone	O
of	O
the	O
speaker	O
to	O
the	O
voice	O
coil	O
bobbin	O
through	O
a	O
compliant	O
section	O
and	O
directly	O
attaching	O
a	O
small	O
lightweight	O
whizzer	B-Device
cone	I-Device
to	O
the	O
bobbin	O
.	O
</s>
<s>
The	O
whizzer	B-Device
cone	I-Device
responds	O
to	O
all	O
frequencies	O
,	O
but	O
due	O
to	O
its	O
smaller	O
size	O
,	O
it	O
only	O
gives	O
a	O
useful	O
output	O
at	O
higher	O
frequencies	O
,	O
thereby	O
implementing	O
a	O
mechanical	B-Algorithm
crossover	I-Algorithm
function	O
.	O
</s>
<s>
Careful	O
selection	O
of	O
materials	O
used	O
for	O
the	O
cone	O
,	O
whizzer	O
and	O
suspension	O
elements	O
determines	O
the	O
crossover	B-Algorithm
frequency	I-Algorithm
and	O
the	O
effectiveness	O
of	O
the	O
crossover	B-Algorithm
.	O
</s>
<s>
Such	O
mechanical	B-Algorithm
crossovers	I-Algorithm
are	O
complex	O
to	O
design	O
,	O
especially	O
if	O
high	O
fidelity	O
is	O
desired	O
.	O
</s>
<s>
As	O
with	O
whizzer	B-Device
cones	I-Device
,	O
careful	O
selection	O
of	O
material	O
,	O
shape	O
and	O
position	O
are	O
required	O
to	O
provide	O
smooth	O
,	O
extended	O
output	O
.	O
</s>
<s>
High	O
frequency	O
dispersion	O
is	O
somewhat	O
different	O
for	O
this	O
approach	O
than	O
for	O
whizzer	B-Device
cones	I-Device
.	O
</s>
<s>
Speakers	O
which	O
use	O
these	O
mechanical	B-Algorithm
crossovers	I-Algorithm
have	O
some	O
advantages	O
in	O
sound	O
quality	O
despite	O
the	O
difficulties	O
of	O
designing	O
and	O
manufacturing	O
them	O
and	O
despite	O
the	O
inevitable	O
output	O
limitations	O
.	O
</s>
<s>
Full-range	B-Device
drivers	I-Device
have	O
a	O
single	O
acoustic	O
center	O
and	O
can	O
have	O
relatively	O
modest	O
phase	O
change	O
across	O
the	O
audio	O
spectrum	O
.	O
</s>
<s>
Nevertheless	O
,	O
within	O
these	O
constraints	O
,	O
cost	O
and	O
complications	O
are	O
reduced	O
,	O
as	O
no	O
crossovers	B-Algorithm
are	O
required	O
.	O
</s>
<s>
Just	O
as	O
filters	O
have	O
different	O
orders	O
,	O
so	O
do	O
crossovers	B-Algorithm
,	O
depending	O
on	O
the	O
filter	O
slope	O
they	O
implement	O
.	O
</s>
<s>
A	O
third	O
-	O
or	O
fourth-order	O
acoustic	O
crossover	B-Algorithm
often	O
has	O
just	O
a	O
second-order	O
electrical	O
filter	O
.	O
</s>
<s>
This	O
requires	O
that	O
speaker	B-Device
drivers	I-Device
be	O
well	O
behaved	O
a	O
considerable	O
way	O
from	O
the	O
nominal	O
crossover	B-Algorithm
frequency	I-Algorithm
,	O
and	O
further	O
that	O
the	O
high-frequency	O
driver	O
be	O
able	O
to	O
survive	O
a	O
considerable	O
input	O
in	O
a	O
frequency	O
range	O
below	O
its	O
crossover	B-Algorithm
point	O
.	O
</s>
<s>
In	O
the	O
discussion	O
below	O
,	O
the	O
characteristics	O
of	O
the	O
electrical	O
filter	O
order	O
are	O
discussed	O
,	O
followed	O
by	O
a	O
discussion	O
of	O
crossovers	B-Algorithm
having	O
that	O
acoustic	O
slope	O
and	O
their	O
advantages	O
or	O
disadvantages	O
.	O
</s>
<s>
Most	O
audio	B-Algorithm
crossovers	I-Algorithm
use	O
first	O
-	O
to	O
fourth-order	O
electrical	O
filters	O
.	O
</s>
<s>
Higher	O
orders	O
are	O
not	O
generally	O
implemented	O
in	O
passive	O
crossovers	B-Algorithm
for	O
loudspeakers	O
but	O
are	O
sometimes	O
found	O
in	O
electronic	O
equipment	O
under	O
circumstances	O
for	O
which	O
their	O
considerable	O
cost	O
and	O
complexity	O
can	O
be	O
justified	O
.	O
</s>
<s>
First-order	O
filters	O
have	O
a	O
20	O
dB/decade	O
(	O
or	O
6	O
dB/octave	O
)	O
slope	O
.	O
</s>
<s>
First-order	O
filters	O
are	O
considered	O
by	O
many	O
audiophiles	O
to	O
be	O
ideal	O
for	O
crossovers	B-Algorithm
.	O
</s>
<s>
This	O
is	O
because	O
this	O
filter	O
type	O
is	O
'	O
transient	O
perfect	O
 '	O
,	O
meaning	O
that	O
the	O
sum	O
of	O
the	O
low-pass	B-Algorithm
and	O
high-pass	O
outputs	O
passes	O
both	O
amplitude	O
and	O
phase	O
unchanged	O
across	O
the	O
range	O
of	O
interest	O
.	O
</s>
<s>
A	O
first-order	O
crossover	B-Algorithm
allows	O
more	O
signal	O
content	O
consisting	O
of	O
unwanted	O
frequencies	O
to	O
get	O
through	O
in	O
the	O
LPF	O
and	O
HPF	O
sections	O
than	O
do	O
higher-order	O
configurations	O
.	O
</s>
<s>
While	O
woofers	B-Device
can	O
easily	O
handle	O
this	O
(	O
aside	O
from	O
generating	O
distortion	O
at	O
frequencies	O
above	O
those	O
that	O
they	O
can	O
properly	O
reproduce	O
)	O
,	O
smaller	O
high-frequency	O
drivers	O
(	O
especially	O
tweeters	B-Device
)	O
are	O
more	O
likely	O
to	O
be	O
damaged	O
,	O
since	O
they	O
are	O
not	O
capable	O
of	O
handling	O
large	O
power	O
inputs	O
at	O
frequencies	O
below	O
their	O
rated	O
crossover	B-Algorithm
point	O
.	O
</s>
<s>
Second-order	O
filters	O
have	O
a	O
40	O
dB/decade	O
(	O
or	O
12	O
dB/octave	O
)	O
slope	O
.	O
</s>
<s>
This	O
order	O
is	O
commonly	O
used	O
in	O
passive	O
crossovers	B-Algorithm
as	O
it	O
offers	O
a	O
reasonable	O
balance	O
between	O
complexity	O
,	O
response	O
,	O
and	O
higher-frequency	O
driver	O
protection	O
.	O
</s>
<s>
When	O
designed	O
with	O
time-aligned	O
physical	O
placement	O
,	O
these	O
crossovers	B-Algorithm
have	O
a	O
symmetrical	O
polar	O
response	O
,	O
as	O
do	O
all	O
even-order	O
crossovers	B-Algorithm
.	O
</s>
<s>
It	O
is	O
commonly	O
thought	O
that	O
there	O
will	O
always	O
be	O
a	O
phase	O
difference	O
of	O
180°	O
between	O
the	O
outputs	O
of	O
a	O
(	O
second-order	O
)	O
low-pass	B-Algorithm
filter	I-Algorithm
and	O
a	O
high-pass	O
filter	O
having	O
the	O
same	O
crossover	B-Algorithm
frequency	I-Algorithm
.	O
</s>
<s>
For	O
passive	O
systems	O
,	O
the	O
tweeter	B-Device
is	O
wired	O
with	O
opposite	O
polarity	O
to	O
the	O
woofer	B-Device
;	O
for	O
active	B-Algorithm
crossovers	I-Algorithm
the	O
high-pass	O
filter	O
's	O
output	O
is	O
inverted	O
.	O
</s>
<s>
In	O
3-way	O
systems	O
the	O
mid-range	B-Device
driver	I-Device
or	O
filter	O
is	O
inverted	O
.	O
</s>
<s>
Third-order	O
filters	O
have	O
a	O
60	O
dB/decade	O
(	O
or	O
18	O
dB/octave	O
)	O
slope	O
.	O
</s>
<s>
These	O
crossovers	B-Algorithm
usually	O
have	O
Butterworth	O
filter	O
characteristics	O
;	O
phase	O
response	O
is	O
very	O
good	O
,	O
the	O
level	O
sum	O
being	O
flat	O
and	O
in	O
phase	O
quadrature	O
,	O
similar	O
to	O
a	O
first-order	O
crossover	B-Algorithm
.	O
</s>
<s>
In	O
the	O
original	O
D'Appolito	O
MTM	B-Device
arrangement	I-Device
,	O
a	O
symmetrical	O
arrangement	O
of	O
drivers	O
is	O
used	O
to	O
create	O
a	O
symmetrical	O
off-axis	O
response	O
when	O
using	O
third-order	O
crossovers	B-Algorithm
.	O
</s>
<s>
Third-order	O
acoustic	O
crossovers	B-Algorithm
are	O
often	O
built	O
from	O
first	O
-	O
or	O
second-order	O
filter	O
circuits	O
.	O
</s>
<s>
Fourth-order	O
filters	O
have	O
an	O
80	O
dB/decade	O
(	O
or	O
24	O
dB/octave	O
)	O
slope	O
.	O
</s>
<s>
These	O
filters	O
are	O
relatively	O
complex	O
to	O
design	O
in	O
passive	O
form	O
,	O
because	O
the	O
components	O
interact	O
with	O
each	O
other	O
,	O
but	O
modern	O
computer-aided	O
crossover	B-Algorithm
optimisation	O
design	O
software	O
can	O
produce	O
accurate	O
designs	O
.	O
</s>
<s>
Steep-slope	O
passive	O
networks	O
are	O
less	O
tolerant	O
of	O
parts	O
value	O
deviations	O
or	O
tolerances	O
,	O
and	O
more	O
sensitive	O
to	O
mis-termination	O
with	O
reactive	O
driver	O
loads	O
(	O
although	O
this	O
is	O
also	O
a	O
problem	O
with	O
lower-order	O
crossovers	B-Algorithm
)	O
.	O
</s>
<s>
A	O
4th-order	O
crossover	B-Algorithm
with	O
−6	O
dB	O
crossover	B-Algorithm
point	O
and	O
flat	O
summing	O
is	O
also	O
known	O
as	O
a	O
Linkwitz-Riley	O
crossover	B-Algorithm
(	O
named	O
after	O
its	O
inventors	O
)	O
,	O
and	O
can	O
be	O
constructed	O
in	O
active	O
form	O
by	O
cascading	O
two	O
2nd-order	O
Butterworth	O
filter	O
sections	O
.	O
</s>
<s>
The	O
low-frequency	O
and	O
high-frequency	O
output	O
signals	O
of	O
the	O
Linkwitz	O
–	O
Riley	O
crossover	B-Algorithm
type	O
are	O
in	O
phase	O
,	O
thus	O
avoiding	O
partial	O
phase	O
inversion	O
if	O
the	O
crossover	B-Algorithm
band-passes	O
are	O
electrically	O
summed	O
,	O
as	O
they	O
would	O
be	O
within	O
the	O
output	O
stage	O
of	O
a	O
multiband	O
compressor	O
.	O
</s>
<s>
Crossovers	B-Algorithm
used	O
in	O
loudspeaker	O
design	O
do	O
not	O
require	O
the	O
filter	O
sections	O
to	O
be	O
in	O
phase	O
;	O
smooth	O
output	O
characteristics	O
are	O
often	O
achieved	O
using	O
non-ideal	O
,	O
asymmetric	O
crossover	B-Algorithm
filter	I-Algorithm
characteristics	O
.	O
</s>
<s>
Bessel	O
,	O
Butterworth	O
,	O
and	O
Chebyshev	O
are	O
among	O
the	O
possible	O
crossover	B-Algorithm
topologies	O
.	O
</s>
<s>
Such	O
steep-slope	O
filters	O
have	O
greater	O
problems	O
with	O
overshoot	O
and	O
ringing	O
but	O
there	O
are	O
several	O
key	O
advantages	O
,	O
even	O
in	O
their	O
passive	O
form	O
,	O
such	O
as	O
the	O
potential	O
for	O
a	O
lower	O
crossover	B-Algorithm
point	O
and	O
increased	O
power	O
handling	O
for	O
tweeters	B-Device
,	O
together	O
with	O
less	O
overlap	O
between	O
drivers	O
,	O
dramatically	O
reducing	O
the	O
shifting	O
of	O
the	O
main	O
lobe	O
of	O
a	O
multi-way	O
loudspeaker	O
system	O
's	O
radiation	O
pattern	O
with	O
frequency	O
,	O
or	O
other	O
unwelcome	O
off-axis	O
effects	O
.	O
</s>
<s>
Passive	O
crossovers	B-Algorithm
giving	O
acoustic	O
slopes	O
higher	O
than	O
fourth-order	O
are	O
not	O
common	O
because	O
of	O
cost	O
and	O
complexity	O
.	O
</s>
<s>
Filters	O
with	O
slopes	O
of	O
up	O
to	O
96	O
dB	O
per	O
octave	B-Language
are	O
available	O
in	O
active	B-Algorithm
crossovers	I-Algorithm
and	O
loudspeaker	O
management	O
systems	O
.	O
</s>
<s>
Crossovers	B-Algorithm
can	O
also	O
be	O
constructed	O
with	O
mixed-order	O
filters	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
second-order	O
low-pass	B-Algorithm
filter	I-Algorithm
can	O
be	O
combined	O
with	O
a	O
third-order	O
high-pass	O
filter	O
.	O
</s>
<s>
A	O
higher-order	O
tweeter	B-Device
crossover	B-Algorithm
can	O
sometimes	O
help	O
to	O
compensate	O
for	O
the	O
time	O
offset	O
between	O
the	O
woofer	B-Device
and	O
tweeter	B-Device
,	O
caused	O
by	O
non-aligned	O
acoustic	O
centers	O
.	O
</s>
<s>
Parallel	O
crossovers	B-Algorithm
are	O
by	O
far	O
the	O
most	O
common	O
.	O
</s>
<s>
This	O
makes	O
two-way	B-Algorithm
crossovers	I-Algorithm
easier	O
to	O
design	O
because	O
,	O
in	O
terms	O
of	O
electrical	O
impedance	O
,	O
the	O
sections	O
can	O
be	O
considered	O
separate	O
and	O
because	O
component	O
tolerance	O
variations	O
will	O
be	O
isolated	O
but	O
like	O
all	O
crossovers	B-Algorithm
,	O
the	O
final	O
design	O
relies	O
on	O
the	O
output	O
of	O
the	O
drivers	O
to	O
be	O
complementary	O
acoustically	O
and	O
this	O
,	O
in	O
turn	O
,	O
requires	O
careful	O
matching	O
in	O
amplitude	O
and	O
phase	O
of	O
the	O
underlying	O
crossover	B-Algorithm
.	O
</s>
<s>
Parallel	O
crossovers	B-Algorithm
also	O
have	O
the	O
advantage	O
of	O
allowing	O
the	O
speaker	B-Device
drivers	I-Device
to	O
be	O
bi-wired	O
,	O
a	O
feature	O
whose	O
benefits	O
are	O
hotly	O
disputed	O
.	O
</s>
<s>
To	O
understand	O
the	O
signal	O
path	O
in	O
this	O
type	O
of	O
crossover	B-Algorithm
,	O
refer	O
to	O
the	O
"	O
Series	O
Crossover	B-Algorithm
"	O
figure	O
,	O
and	O
consider	O
a	O
high-frequency	O
signal	O
that	O
,	O
during	O
a	O
certain	O
moment	O
,	O
has	O
a	O
positive	O
voltage	O
on	O
the	O
upper	O
Input	O
terminal	O
compared	O
to	O
the	O
lower	O
Input	O
terminal	O
.	O
</s>
<s>
The	O
low-pass	B-Algorithm
filter	I-Algorithm
presents	O
a	O
high	O
impedance	O
to	O
the	O
signal	O
,	O
and	O
the	O
tweeter	B-Device
presents	O
a	O
low	O
impedance	O
;	O
so	O
the	O
signal	O
passes	O
through	O
the	O
tweeter	B-Device
.	O
</s>
<s>
The	O
signal	O
continues	O
to	O
the	O
connection	O
point	O
between	O
the	O
woofer	B-Device
and	O
the	O
high-pass	O
filter	O
.	O
</s>
<s>
A	O
low-frequency	O
signal	O
with	O
a	O
similar	O
instantaneous	O
voltage	O
characteristic	O
first	O
passes	O
through	O
the	O
LPF	O
,	O
then	O
the	O
woofer	B-Device
,	O
and	O
appears	O
at	O
the	O
lower	O
Input	O
terminal	O
.	O
</s>
<s>
Derived	O
crossovers	B-Algorithm
include	O
active	B-Algorithm
crossovers	I-Algorithm
in	O
which	O
one	O
of	O
the	O
crossover	B-Algorithm
responses	O
is	O
derived	O
from	O
the	O
other	O
through	O
the	O
use	O
of	O
a	O
differential	O
amplifier	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
difference	O
between	O
the	O
input	O
signal	O
and	O
the	O
output	O
of	O
the	O
high-pass	O
section	O
is	O
a	O
low-pass	B-Algorithm
response	O
.	O
</s>
<s>
Thus	O
,	O
when	O
a	O
differential	O
amplifier	O
is	O
used	O
to	O
extract	O
this	O
difference	O
,	O
its	O
output	O
constitutes	O
the	O
low-pass	B-Algorithm
filter	I-Algorithm
section	O
.	O
</s>
<s>
The	O
main	O
advantage	O
of	O
derived	O
filters	O
is	O
that	O
they	O
produce	O
no	O
phase	O
difference	O
between	O
the	O
high-pass	O
and	O
low-pass	B-Algorithm
sections	O
at	O
any	O
frequency	O
.	O
</s>
<s>
that	O
the	O
response	O
of	O
one	O
or	O
both	O
sections	O
peaks	O
near	O
the	O
crossover	B-Algorithm
frequency	I-Algorithm
,	O
or	O
both	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
(	O
1	O
)	O
,	O
above	O
,	O
the	O
usual	O
situation	O
is	O
that	O
the	O
derived	O
low-pass	B-Algorithm
response	O
attenuates	O
at	O
a	O
much	O
slower	O
rate	O
than	O
the	O
fixed	O
response	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
(	O
2	O
)	O
,	O
above	O
,	O
both	O
speakers	O
are	O
required	O
to	O
operate	O
at	O
higher	O
volume	O
levels	O
as	O
the	O
signal	O
nears	O
the	O
crossover	B-Algorithm
points	O
.	O
</s>
<s>
Some	O
may	O
focus	O
on	O
woofer/cabinet	O
design	O
and	O
issues	O
related	O
to	O
cabinet	O
volume	O
and	O
ports	O
(	O
if	O
any	O
)	O
,	O
while	O
others	O
may	O
focus	O
on	O
the	O
crossover	B-Algorithm
and	O
frequency	O
response	O
.	O
</s>
<s>
In	O
the	O
period	O
before	O
computer	O
modeling	O
made	O
it	O
affordable	O
and	O
quick	O
to	O
simulate	O
the	O
combined	O
effects	O
of	O
drivers	O
,	O
crossovers	B-Algorithm
and	O
cabinets	B-Device
,	O
a	O
number	O
of	O
issues	O
could	O
go	O
unnoticed	O
by	O
the	O
speaker	O
designer	O
.	O
</s>
<s>
For	O
instance	O
,	O
simplistic	O
three-way	B-Algorithm
crossovers	I-Algorithm
were	O
designed	O
as	O
a	O
pair	O
of	O
two-way	B-Algorithm
crossovers	I-Algorithm
:	O
the	O
tweeter/mid	O
-range	O
and	O
the	O
other	O
the	O
mid-range/woofer	O
sections	O
.	O
</s>
