COMMON ENCLOSURE TYPES
In the car audio world there are 5 types of subwoofer enclosures commonly used; INFINITE
BAFFLE, SEALED BOX (closed box), VENTED BOX (bass reflex), SINGLE-VENTED
(often incorrectly referred to as “5th” order), and DUAL-VENTED
(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
name
implies a “built-in” acoustical response which
has a
natural
response 30 Hz for
example) but also a
response suppressing high frequencies
Hz for example).
INFINITE BAFFLE 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 capability and
substandard transient response.
SEALED boxes offer one of the best compromises in power
handling and performance. Because of the “air spring”
provided by the box the advantaqes include simple box
construction, high power handling, excellent transient
response, and smooth low frequency roll-off. Disadvantaaes
include only moderate efficiencies at low frequencies and the
need for large box volumes.
VENTED boxes extend the low frequency response below
that of the sealed box by using a port tube. Advantaaes
include extended low frequency response, lower distortion
due to smaller cone movements, good efficiency, good
transient response: moderate size boxes, and high 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
boxes are relatively new
(about 5 years in the car) but offer some advantages of both
the sealed and vented designs. Advantaaes include good
efficiency, small box volumes, good transient response,
extended low frequency performance, and can be used with
very high power amplifiers. Disadvantages include slightly
lower efficiency compared to a vented box and increased
complexity in box design and construction.
DUAL-VENTED
boxes vent the sound from the
front and back of the woofer through individually tuned
enclosure on the front and rear of the woofer. The
advantaqe 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 strong susceptibilities to’cone over-excursions (damage)
for sound outside its primary frequency band.