The effects of low tuning in a smaller enclosure:
While larger
enclosures combined
with low tuning will
provide the most
extended response,
the same concept can
be applied to smaller
enclosures as well.
Using the same driver
as in the previous
examples, let's
consider venting the
sealed enclosure
volume and tuning to
23 Hz. This resulted in
the red curve shown.
Note that the initial roll
off very closely
emulates the  
response (orange) of
the sealed alignment,
but lower in frequency.
This results in an f3
being 10 Hz lower, and
3 dB more output at 20 Hz than the sealed alignment.
The smaller enclosure
with the lower tuning
results in the (red)
vented GD increasing
above the sealed GD
similar to the larger
vented alignment, but
still not equaling twice
the sealed GD until
below 25 Hz. The
additional phase
rotation is only 60
degrees at 20 Hz.
There are a couple of
tradeoffs will low tuned
vented alignments. One
issue is of course the
longer port length and its
attendant possibility of
pipe resonances. As
demonstrated in the port
velocity plot to the right
the air velocity will
generally be lower,
however, and the peak of
the vent output will be
generally below any
musical content. It's been
my experience that pipe
resonances are rarely
audible in this type of
alignment, especially
when the vent is at the
rear of bottom of the
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