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COMMON ENCLOSURE TYPES
In the car audio world there are five types of subwoofer enclosures commonly used: INFINITE
BAFFLE, SEALED BOX (closed box), VENTED BOX (bass reflex), SINGLE-VENTED BANDPASS
(often incorrectly referred to as "5th" order), DUAL-VENTED BANDPASS (often incorrectly referred
to as "7th" order). No single design is superior because each has its own compromise in performance,
power handling and design complexity. The bandpass name implies a "built-in" acoustical response
which has a natural highpass response (30 Hz for example) but also a lowpass response suppressing
high frequencies (e.g., > 80 Hz).
INFINITE BAFFLE (fig. a) designs simply use the trunk of the car for
its acoustical enclosure and the rear deck to isolate the front and rear
sound paths. Advantages include simple installation and adequate
performance for most systems. Disadvantages include poor power
handling capacity and substandard transient response.
SEALED boxes (fig. b) offer one of the best compromises in power
handling and performance. Because of the "air spring" provided by the
box the advantages include simple box construction, higher power
handling, excellent transient response, and smooth low frequency roll-
off. Disadvantages include only moderate efficiencies at low frequen-
cies and the need for large box volumes.
VENTED boxes (fig. c) extend the low frequency response below that
of the sealed box by using a port tube. Advan-tages include extended
low frequency response, lower distortion due to smaller cone move-
ments in its passband, good efficiency, good transient response,
moderate size boxes and higher power capacity. Disadvantages
include increased complexity in box design and possible woofer
damage due to over-excursion of the woofer cone below the cut-off
frequency of the vented box.
SINGLE-VENTED BANDPASS boxes (fig. d) are relatively new
(about 5 years in the car) but offer some advantages of both the sealed
and vented designs. Advantages include reasonable efficiency, small
box volumes, good transient response, extended low frequency per-
formance and can be used with very high power amplifiers. Disadvan-
tages include slightly lower efficiency compared to a vented box and
increased complexity in box design and construction.
DUAL-VENTED BANDPASS boxes (fig. e) vent the sound from the
front and back of the woofer through individually tuned enclosure on the
front and rear of the woofer. The advantage of this design is its high
efficiency over a narrow frequency band. Disadvantages include
complex design and construction, large box volumes, poor transient
response and susceptibilities to cone over-excursions (damage) for
sound outside its primary frequency band.
a)
b)
c)
d)
e)
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