<s>
HD77	B-Device
is	O
a	O
model	O
name	O
of	O
Marantz	O
4-way	O
high-fidelity	O
loudspeakers	O
which	O
were	O
produced	O
during	O
the	O
mid-1970s	O
.	O
</s>
<s>
They	O
were	O
bass	O
reflex	O
speakers	O
,	O
but	O
came	O
with	O
a	O
cylindrical	O
piece	O
of	O
foam	O
which	O
fit	O
into	O
the	O
bass-reflex	O
port	O
of	O
the	O
enclosure	B-Device
if	O
the	O
listener	O
preferred	O
the	O
more	O
accurate	O
bass	O
response	O
provided	O
by	O
airtight	O
speaker	B-Device
boxes	I-Device
.	O
</s>
<s>
Marantz	B-Device
HD77s	I-Device
had	O
a	O
total	O
volume	O
of	O
each	O
.	O
</s>
<s>
The	O
four	O
drivers	O
of	O
the	O
Marantz	B-Device
HD77s	I-Device
are	O
a	O
woofer	B-Device
,	O
mid-range	O
,	O
tweeter	B-Device
and	O
super	B-Device
tweeter	I-Device
.	O
</s>
<s>
The	O
mid-range	O
,	O
tweeter	B-Device
and	O
super	B-Device
tweeter	I-Device
have	O
crossover	O
controls	O
for	O
switching	O
between	O
a	O
laboratory	O
"	O
flat	O
"	O
+	O
/	O
-	O
0db	O
neutral	O
response	O
and	O
a	O
"	O
room	O
EQ	O
"	O
response	O
.	O
</s>
<s>
Without	O
crossover	O
points	O
,	O
the	O
drivers	O
would	O
distort	O
and	O
likely	O
overheat	O
and	O
burn	O
out	O
due	O
to	O
the	O
production	O
of	O
the	O
full	O
spectrum	O
of	O
frequencies	O
,	O
with	O
exception	O
of	O
the	O
woofer	B-Device
which	O
inherently	O
struggles	O
with	O
producing	O
higher	O
frequencies	O
.	O
</s>
<s>
The	O
woofer	B-Device
is	O
in	O
diameter	O
with	O
a	O
frequency	O
response	O
of	O
30	O
to	O
500	O
hertz	O
.	O
</s>
<s>
The	O
tweeter	B-Device
is	O
a	O
LPF	O
film	O
dome-type	O
.	O
</s>
<s>
The	O
tweeter	B-Device
's	O
frequency	O
response	O
is	O
from	O
3	O
kHz	O
to	O
8kHz	O
.	O
</s>
<s>
The	O
super	B-Device
tweeter	I-Device
is	O
a	O
1-inch	O
LPF	O
film	O
dome	O
with	O
response	O
from	O
8	O
to	O
23	O
kHz	O
,	O
which	O
extends	O
3	O
kHz	O
above	O
the	O
nominal	O
range	O
of	O
audio	O
frequencies	O
which	O
can	O
be	O
heard	O
by	O
the	O
human	O
ear	O
.	O
</s>
