The response plot to
the right shows the
Dayton RS225 driver
in a sealed alignment,
and two vented
alignments. The
orange response
represents a sealed
alignment with a Qtc of
.707, or maximally flat
response. The green
plot is a vented QB3
alignment, and the
blue curve is a vented
alignment of my
choosing. -More about
that later. At first
glance the vented
alignment represented
by the green response
might appear to be the
best choice, as it
provides the lowest  
The group delay of a typical driver in different alignments:
This plot shows the
effect of the three
enclosures on the
transfer function
phase. The orange
plot shows the 180
degree phase wrap
expected of a sealed
alignment while the
two vented designs
will ultimately both
end up with 360
degrees of phase
wrap indicative of the
4th order transfer
function. Note the
consequently faster
rate of change at
some frequencies
(but not all) for the
vented designs, which
will result in greater
group delay.
And finally the group
delay plot. This clearly
shows the greater
group delay of the two
vented designs, but
the differences require
a little closer scrutiny.
Note that above
roughly 120 Hz the GD
delays are the same,
and below that point
the GD of the vented
alignments is actually
slightly better than the
sealed alignment. Of
course at lower
frequencies the vented
GD starts to increase
rapidly, but note the
frequencies in relation
to the musical content
in typical music.
Many consider accurate reproduction down to 40 Hz sufficient for most music, and many musical venues
have little content below that frequency. Note that even in this context, the GD of the QB3 alignment (green)
has almost doubled in relation to the sealed alignment by 40 Hz.

Now lets look at the alignment indicated by the blue line. Looking at the GD plot, the vented delay doesn't
exceed the sealed design until 44 Hz, and does not approach twice the GD of the sealed design until 26 Hz.
At 20 Hz, the GD of the vented design represents only an additional 90 degrees of phase rotation. Looking
back at the response plot, we see the f3 of the blue vented design is more than 10 Hz lower, while its f9 is
below 20 Hz, and has nearly 8 dB more output at this frequency. The 'blue' alignment was determined in this
case by using the QB3 enclosure volume, but lowering the tuning to obtain a 6 dB/octave roll off between 20
and 40 Hz. While this is not the flattest alignment, it may better compensate for room modes, provide a
flatter overall in room response, and represent an acceptable compromise between low end extension and
group delay. Cone excursion of this vented alignment is roughly equal to or less than the sealed design until
below 15 Hz, where there will be little or no  musical content. This resulted in a 63 liter enclosure tuned to 18
Hz compared to 33 liters for the sealed.
maximally flat extension before rolling off. -But in light of GD and other considerations, is it really?
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