Some obversations on
Sealed vs. Vented
1 < Page > 3
Excessive Group Delay is a big concern in vented designs:
Of course GD is always larger with a vented design, but how much larger and how significant is it,
really? In the group delay plot below, note the sealed has a maximum of 5.7 mSec. The vented group
delay does not reach twice that delay until 22 Hz. This represents an additional phase rotation of 43.5
degrees for the vented alignment. At 40 Hz, the group delay differential is only 30 degrees.
Vented enclosures are always larger than their sealed counterparts:
While to obtain maximum low-end extension, this statement is certainly true. However, all of the vented
examples shown above were modeled in the same volume enclosure as the sealed example: 36 liters,
and tuned to 20 Hz.
Sealed has better transient response than vented.
This is a true statement, and another manifestation of the 4th order alignment. The only way a vented
design can have as good of transient response is a sealed design is to tune the vent to 0 Hz. -In
other words remove the vent. However, as the vent tuning is lowered, transient response improves.
Consider the tone burst plot below.
In a burst plot, a sine wave is suddenly started at the origin (0 volts) and stops just as fast after a few
cycles. The light blue trace is the input signal, and of course the ideal driver would track this
response perfectly. Unfortunately, trivial details such as mass and inertia get in the way, so this
doesnt happen. The cone takes a cycle or so to get up to speed, and likewise when the signal stops.
How quickly it responds to the changes is an indication of its transient response. The magenta trace
is the RS225 in the sealed enclosure Qtc .707. The white trace is the vented enclosure described
previously. The Green trace is the RS225 in a traditional QB3 alignment. Note that while the low
tuned alignment is not quite as good as the sealed alignment, it is far superior to the QB3 response,
-which, although not shown, oscillates for yet another half cycle before settling down.