<s>
A	O
bookshelf	B-Device
loudspeaker	I-Device
(	O
or	O
bookshelf	B-Device
speaker	I-Device
)	O
is	O
a	O
compact	O
loudspeaker	O
,	O
generally	O
sold	O
for	O
consumer-grade	O
home	O
audio	O
applications	O
as	O
part	O
of	O
a	O
shelf	O
stereo	O
pair	O
or	O
home	O
theater	O
package	O
,	O
that	O
is	O
compact	O
in	O
size	O
and	O
intended	O
to	O
be	O
placed	O
on	O
a	O
raised	O
surface	O
,	O
e.g.	O
</s>
<s>
In	O
the	O
1950s	O
and	O
1960s	O
,	O
high	O
quality	O
home	O
loudspeakers	O
were	O
exclusively	O
large	O
and	O
floor-standing	O
speaker	B-Device
enclosures	I-Device
,	O
whereas	O
small	O
speaker	B-Device
cabinets	I-Device
had	O
reputation	O
of	O
low	O
price	O
and	O
low	O
audio	O
quality	O
.	O
</s>
<s>
The	O
demand	O
for	O
smaller	O
speakers	O
was	O
from	O
hifi	O
enthusiasts	O
who	O
lived	O
in	O
small	O
apartments	O
,	O
who	O
did	O
not	O
have	O
space	O
for	O
large	O
speaker	B-Device
enclosures	I-Device
.	O
</s>
<s>
Edgar	O
Villchur	O
,	O
who	O
along	O
with	O
partner	O
Henry	O
Kloss	O
founded	O
Acoustic	O
Research	O
,	O
is	O
generally	O
credited	O
with	O
inventing	O
bookshelf	B-Device
speakers	I-Device
.	O
</s>
<s>
Villchur	O
's	O
key	O
innovation	O
was	O
an	O
acoustic	B-Architecture
suspension	I-Architecture
(	O
also	O
called	O
"	O
sealed	O
box	O
"	O
)	O
design	O
,	O
by	O
which	O
the	O
woofer	B-Device
and	O
other	O
drivers	B-Device
were	O
in	O
separately	O
enclosed	O
chambers	O
.	O
</s>
<s>
The	O
speaker	B-Device
drivers	I-Device
were	O
stiffer	O
and	O
much	O
smaller	O
than	O
the	O
earlier	O
ported	O
designs	O
.	O
</s>
<s>
The	O
acoustic	B-Architecture
suspension	I-Architecture
design	O
enabled	O
the	O
air	O
in	O
the	O
sealed	O
box	O
to	O
act	O
like	O
a	O
spring	O
,	O
to	O
help	O
prevent	O
excessive	O
excursion	O
.	O
</s>
<s>
Certain	O
market	O
and	O
technical	O
issues	O
have	O
contributed	O
to	O
the	O
widespread	O
adoption	O
of	O
bookshelf	B-Device
speakers	I-Device
in	O
the	O
1990s	O
and	O
beyond	O
.	O
</s>
<s>
Technical	O
improvements	O
and	O
less	O
expensive	O
mass-production	O
technologies	O
have	O
made	O
high-quality	O
bookshelf	B-Device
speakers	I-Device
affordable	O
for	O
most	O
audio	O
enthusiasts	O
.	O
</s>
<s>
Rapid	O
improvements	O
in	O
amplifiers	O
,	O
digital	B-Architecture
signal	I-Architecture
processors	I-Architecture
and	O
other	O
components	O
has	O
improved	O
the	O
sound	O
quality	O
of	O
low	O
to	O
mid-level	O
home	O
audio	O
systems	O
,	O
which	O
creates	O
a	O
stronger	O
need	O
for	O
adequate	O
speakers	O
.	O
</s>
<s>
For	O
cost	O
and	O
practical	O
reasons	O
the	O
most	O
common	O
setup	O
is	O
satellite	O
speakers	O
,	O
typically	O
bookshelf	B-Device
speakers	I-Device
for	O
the	O
side	O
,	O
back	O
,	O
and	O
sometimes	O
the	O
front	O
and	O
center	O
channels	O
,	O
rather	O
than	O
larger	O
speakers	O
for	O
each	O
channel	O
.	O
</s>
<s>
Finally	O
,	O
most	O
home	O
theater	O
and	O
many	O
musical	O
home	O
audio	O
applications	O
,	O
began	O
in	O
the	O
late	O
1990s	O
to	O
incorporate	O
separately-enclosed	O
subwoofers	B-Application
to	O
handle	O
deep	O
bass	O
.	O
</s>
<s>
Human	O
perception	O
of	O
low-frequency	O
sound	O
is	O
relatively	O
non-directional	O
,	O
so	O
a	O
single	O
subwoofer	B-Application
cabinet	O
placed	O
anywhere	O
in	O
the	O
room	O
(	O
even	O
hidden	O
behind	O
a	O
sofa	O
)	O
is	O
usually	O
sufficient	O
and	O
may	O
be	O
placed	O
anywhere	O
.	O
</s>
<s>
Without	O
the	O
relatively	O
heavy	O
,	O
bulky	O
,	O
and	O
expensive	O
low	O
bass	O
drivers	B-Device
and	O
their	O
large	O
speaker	B-Device
enclosures	I-Device
,	O
the	O
speakers	O
can	O
be	O
made	O
smaller	O
.	O
</s>
