Some obversations on
Sealed vs. Vented
enclosure designs...
Sealed vs. Vented
enclosure designs...
This will not be an exhaustive article on the Helmholtz effects. This has been well covered in many other
articles. Instead this will be a look into certain generalizations of the vented design, and demonstrate a
non-traditional alignment for consideration.
There has always been some confusion in understanding what exactly happens when we put a hole in a
sealed box, and how the effects of different alignments relate to the various parameters. One misconception
is the resultant increased efficiency, which often is taken to mean increased sensitivity.
The output of a given driver at frequencies above fb will be exactly the same for either sealed or vented
design. The additional low frequency output provided by the vent is the result of this increased efficiency.
This is demonstrated on the plot below: The modeled driver is an RS225-8, and the identical source voltage
drives both models. The yellow plot is the sealed alignment with a Qtc of .707, while the green one is a
vented alignment
articles. Instead this will be a look into certain generalizations of the vented design, and demonstrate a
non-traditional alignment for consideration.
There has always been some confusion in understanding what exactly happens when we put a hole in a
sealed box, and how the effects of different alignments relate to the various parameters. One misconception
is the resultant increased efficiency, which often is taken to mean increased sensitivity.
The output of a given driver at frequencies above fb will be exactly the same for either sealed or vented
design. The additional low frequency output provided by the vent is the result of this increased efficiency.
This is demonstrated on the plot below: The modeled driver is an RS225-8, and the identical source voltage
drives both models. The yellow plot is the sealed alignment with a Qtc of .707, while the green one is a
vented alignment
Another misconception would be that sealed boxes always play louder than vented ones. This
generalization is certainly true in some instances, but it is not always correct. The plot below shows the
excursion of the vented driver to be equal or less than the sealed driver until some frequency far below 20
Hz. At that frequency, the cone unloading would be outside the passband of normal music content, and
would not be excited. If the driver selected required higher vent tunings cone unloading would of course, be
of more concern, but could be ameliorated by an active or passive high pass filter. Note that while the
vented excursion is within 115% of its Xmax, the source voltage would have to be reduced to keep the
sealed excursion within its Xmax parameters. Consequently, the sealed speaker would have about 2 dB less
max SPL than the vented alignment. .
generalization is certainly true in some instances, but it is not always correct. The plot below shows the
excursion of the vented driver to be equal or less than the sealed driver until some frequency far below 20
Hz. At that frequency, the cone unloading would be outside the passband of normal music content, and
would not be excited. If the driver selected required higher vent tunings cone unloading would of course, be
of more concern, but could be ameliorated by an active or passive high pass filter. Note that while the
vented excursion is within 115% of its Xmax, the source voltage would have to be reduced to keep the
sealed excursion within its Xmax parameters. Consequently, the sealed speaker would have about 2 dB less
max SPL than the vented alignment. .
Vented designs roll off 4th order, or 24 dB/octave. -Twice that of a sealed design:
Well of course this is ultimately true, but often the alignment can be manipulated to emulate much lower
transfer functions for a significant portion of the frequency band.
Note in the response pic above the vented (green) response closely follows the sealed response to well
below f10. In this instance a larger enclosure with the same tuning would result in an even shallower roll off
and still lower f3/f10 frequencies.
Continued...
Well of course this is ultimately true, but often the alignment can be manipulated to emulate much lower
transfer functions for a significant portion of the frequency band.
Note in the response pic above the vented (green) response closely follows the sealed response to well
below f10. In this instance a larger enclosure with the same tuning would result in an even shallower roll off
and still lower f3/f10 frequencies.
Continued...
0 < Page > 2
