<s>
The	O
effect	O
varied	O
according	O
to	O
amplitude	B-Application
.	O
</s>
<s>
In	O
a	O
3-way	O
loudspeaker	O
system	O
,	O
with	O
tweeter	B-Device
,	O
woofer	B-Device
,	O
and	O
mid-range	B-Device
speaker	I-Device
,	O
a	O
presence	O
control	O
is	O
simply	O
a	O
volume	O
control	O
for	O
the	O
mid-range	B-Device
speaker	I-Device
.	O
</s>
