Woofer Enclosure Designs
| When it comes to producing boom, The woofer and amplifier are usually the center of attention. Another element that is equally important is the woofer enclosure. If you have a great subwoofer and mount it in a a poorly designed box, you will get some pretty pitiful bass. Iwthout the proper box you never will experience the full potential of your amp and woofer. Below are diagrams and info on some of the different types of enclosure available. Which is best will depend on your individual woofer. |
Infinite Baffle (Free Air)
Accomplished by mounting speakers to a board and using the trunk as an enclosure. MUST BE SEALED to prevent air moving from the front to the back of the speakers. Requires a speaket with a Qts of .6 or more and a Vas lower than the volume of the trunk area available.
PROS
- Low Cost
- Takes up little space in trunk
- Simple construction
CONS
- Requires more power
- Sometimes difficult to completely seal
front to eliminate bass cancellation
- Less accurate
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Sealed (Acoustic Suspension)
Accomplished by mounting speakers in a completely sealede enclosure. When a volume of air in a sealed box is less than the Vas of the driver, the air trapped within acts as an acoustic spring to help control the speaker. Requies a speaker with a Qts between .3 and .9 and a Fs below 40 Hz.
PROS
- High power handling
- More forgiving on exact box size
- Simple construction
- Smooth frequency response
- Excellent cone control (restoring force)
CONS
- Requires more power
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Vented (Ported)
Also known as Bass Reflex, Tuned or Tuned Port enclosures. Essentially a sealed box with an opening that allows the back wave from the speaker to interact with the front. By changing the length or surface area of the opening, you change the tuning frequency of the enclosure. Requires a speaker with a Qts between .1 and .4 and a low Fs (30-40 Hz).
PROS
- Higher output
- Deeper bass extension
- Near the tuning frequency, almost all
output is generated by the vent so cone
is controlled to the point of almost no
movement.
CONS
- Requires accuarate calculation for box
size and vent area (size and length).
- Below tuning frequency, the enclosure
no longer controls the woofer and the
cone will act like it has no baffle. This
will produce almost non-existant bass.
The result is an unstable woofer that
oscillates violently, usually causing
woofer failure.
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Front to Front
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Back to Back
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Front to Back
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This application is really more of a method of mounting woofers than an enclosure design. This design utilizes a sealed enclosure An isobaric system is accomplished by combining two woofers to act as one. The woofer may be mounted face to face (must be far apart enough to prevent them from stiking one another), back to back or front to back. An isobaric system requires only half the enclosure volume compared to what a single woofer would need. This is because the Vas is half the single driver due to having two suspensions on the same diaphragm. The woofer must move in phase (move in the same direction) with one another. If the woofers are mounted front to back or back to back, one of the woofers leads must be reversed with respect to the other woofer.
PROS
- Takes up very little room
- Simple construction
- Very tight, accurate bass
- Two isobaric systems would take up about the same amount of space as a single woofer, so you could gain 3 dB more output due to the
increase in cone area.
CONS
- Requires twice the power and two woofers just to get the same output that one woofer would generate in a normal sized sealed
enclosure. |
Bandpass enclosures fall into two basic groups - Single Reflex and Dual Reflex. In a bandpass enclosure, the woofer is mounted inside a box and all the sound exits out the port(s) of the box.
PROS
- T his design exhibits ghigh efficiency over a select range of frequencies
- Unwanted midbass and higher frequencies can be filtered out because of the narrow range of frwquencies that the port produces.
CONS
- Due tio the fact that all the sound is produced by the port(s), the sound quality is usually not as accurate and tight as a correctly designed sealed or ported enclosure.
- Decreased power handling for the woofers
- Larger size requirement for the enclosure
Easier to damage woofer because it is more difficult to detect when the amp is clipping, due to the inaccuarcy of the bass produced by
this type of enclosure.
- Most complex and demanding design to build. If tuned incorrectly, damge to the woofers is inevitable. |
Single Reflex (4th Order)
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Dual Reflex (6th Order)
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Series Tuned Dual Reflex (6th Order)
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Iso 4th Order
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Dual Reflex (6th Order)
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Series Tuned Dual Reflex (6th Order)
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| When discussing enclosure design, you may hear orders referenced in the conversation. The Order refers to the type of design. The following is the most accepted rule of orders for enclosures. There are some differing opinions with some of the bandpass type (which we'll point out). The number of the order will be increased by one if a passive low pass crossover (coil, also called a choke) is encorporated into the enclosure/subwoofer system. For example, if we add a coil to a 4th order set-up, it would be considered a 5th order enclosure. |
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