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Home Theater Programming Sources
Off-Air TV
Types of Subwoofers
There are three main types of subwoofer enclosures: bass reflex (ported box), acoustic
suspension (sealed box) and bandpass. The bandpass enclosure is actually a combination
of enclosure types. A bandpass enclosure has the woofer inside the box so that the bass
output comes entirely from one or more ports.
The three types of enclosures are heavily represented in the marketplace. There are
examples of high quality subwoofers that use each type of speaker enclosure. Each type
has advantages and disadvantages.
Subwoofer Enclosure Types
Acoustic Suspension (sealed box) –
This is the simplest type of subwoofer enclosure to design and build. It has been around
for a long time and is a very mature type. The acoustic suspension enclosure type was
invented by Acoustic Research in the 1950’s.
Advantages-
Disadvantages
Bass Reflex (ported box) –
The bass reflex design uses a port to tune the enclosure to the desired frequency. The
port volume causes the column of air in the port to resonate at specific frequency. This is
used, in combination with the enclosure size, to tune the subwoofer enclosure to a specific
frequency.
As the bass notes get lower and approach the tuning frequency of the enclosure, more of
the bass output comes from the port, and less comes from the woofer cone itself. In
addition, as the frequency becomes lower, and approaches the tuning frequency, the
speaker excursion becomes lower. The speaker excursion actually approaches zero at the
tuning frequency. This decrease in speaker cone movement is what contributes to the bass
reflex design’s low distortion at and near the system tuning frequency.
The passive radiator design is actually a type of bass reflex enclosure.
Advantages
Disadvantages
Bandpass -
The bandpass enclosure is essentially two enclosures in one. One is behind the woofer as
in a traditional subwoofer. The other is in front of the woofer and is vented through one or
more tuned ports. The rear enclosure may be either sealed (single reflex) or ported (dual
reflex). Bandpass subwoofer enclosures yield low distortion and high output at the cost of
construction complexity and a larger enclosure size. They can also have a "one note"
quality to the bass and sound "boomy" on some occasions.
There are three main types of subwoofer enclosures: bass reflex (ported box), acoustic
suspension (sealed box) and bandpass. The bandpass enclosure is actually a combination
of enclosure types. A bandpass enclosure has the woofer inside the box so that the bass
output comes entirely from one or more ports.
The three types of enclosures are heavily represented in the marketplace. There are
examples of high quality subwoofers that use each type of speaker enclosure. Each type
has advantages and disadvantages.
Subwoofer Enclosure Types
Acoustic Suspension (sealed box) –
This is the simplest type of subwoofer enclosure to design and build. It has been around
for a long time and is a very mature type. The acoustic suspension enclosure type was
invented by Acoustic Research in the 1950’s.
Advantages-
- Simple to build
- Shallow low frequency roll off
- “tight” sounding bass
- Good power handling below the system tuning frequency
Disadvantages
- Lower bass output at and above the system tuning frequency compared to bass
reflex design - Higher driver excursion, and possibly distortion, at and above the system tuning
frequency compared to a bass reflex design.
Bass Reflex (ported box) –
The bass reflex design uses a port to tune the enclosure to the desired frequency. The
port volume causes the column of air in the port to resonate at specific frequency. This is
used, in combination with the enclosure size, to tune the subwoofer enclosure to a specific
frequency.
As the bass notes get lower and approach the tuning frequency of the enclosure, more of
the bass output comes from the port, and less comes from the woofer cone itself. In
addition, as the frequency becomes lower, and approaches the tuning frequency, the
speaker excursion becomes lower. The speaker excursion actually approaches zero at the
tuning frequency. This decrease in speaker cone movement is what contributes to the bass
reflex design’s low distortion at and near the system tuning frequency.
The passive radiator design is actually a type of bass reflex enclosure.
Advantages
- Good output at and above the system tuning frequency
- Low distortion at and above the system tuning frequency
Disadvantages
- More complicated to design and build
- Under the system tuning frequency the woofer becomes unloaded, substantially
lowering output and power handling while dramatically increasing distortion.
Bandpass -
The bandpass enclosure is essentially two enclosures in one. One is behind the woofer as
in a traditional subwoofer. The other is in front of the woofer and is vented through one or
more tuned ports. The rear enclosure may be either sealed (single reflex) or ported (dual
reflex). Bandpass subwoofer enclosures yield low distortion and high output at the cost of
construction complexity and a larger enclosure size. They can also have a "one note"
quality to the bass and sound "boomy" on some occasions.
Single Reflex Bandpass Subwoofer Enclosure
Things to consider when evaluating a home theater subwoofer:
- Bass extension - Many of the subwoofers on the market today are, in reality,
only powered woofers. They have a comparative lack of bass extension, only
reaching down to 35 - 40hz or so. A true subwoofer should cover the lowest
octave, which is the range from 20Hz - 40Hz. Having said this, many motion
picture sound tracks and much music has little information in this region. In any
case, having never experienced truly low bass, many people mistake bass in
the 40Hz - 60Hz region as "really low bass". Quite a few subwoofers will provide
decent output in that range and merely reproduce the first harmonic of the
lower bass notes. Many people mistake the first harmonic, which is double the
frequency of the actual, or fundamental, note, for output at the lowest
frequencies. - Low Distortion - Reproducing low bass requires the movement of large
quantities of air. This entails either using a very large woofer cone or making a
smaller cone travel a long way in and out. The in and out motion of a speaker
is known as excursion. When a speaker cone has a long excursion it can move
more air, but it is more difficult for the motion to remain linear, that is have
motion directly proportional to the input signal. - Output - If your subwoofers don't have enough output you won't get that
dramatic punch you are looking for in your home theater. For example, the
THX reference level for the LFE channel in a Dolby Digital 5.1 system is 115db.
115db is extremely loud for bass reproduction. The larger your theater, the
more output from your subwoofers will be required to energize the room to that
level. In any case, it is important for your subwoofer to be able to accurately
reproduce low bass at a fairly high volume level to achieve a sense of realism. - For most people there are three other factors to consider - Size, build quality
and price. A larger subwoofer usually has better low frequency extension and
output, but If it's too large it can be a hassle to put it in your theater. There are
so many different subwoofers out there, you can find one that meets your
criteria.
If you're looking for an excellent subwoofer for any purpose, weather
your primary listening is for home theater or music, you really should give
Axiom Audio subwoofers a try. They are factory direct, so you avoid an
extra layer of price markup and get a great value. They also sound
fantastic and have first rate build quality. They are consistently top rated
subs from many different speaker reviewers. Check them out at Axiom
Audio Subwoofers.
your primary listening is for home theater or music, you really should give
Axiom Audio subwoofers a try. They are factory direct, so you avoid an
extra layer of price markup and get a great value. They also sound
fantastic and have first rate build quality. They are consistently top rated
subs from many different speaker reviewers. Check them out at Axiom
Audio Subwoofers.
Copyright 2004-6 1 touch movie.com
Home theater and Automation Guide
All rights reserved.
Home theater and Automation Guide
All rights reserved.
Types of Subwoofer Enclosures
1 Touch Movie.com