This section describes some elements necessary for understanding subwoofers - how they operate, how to build proper enclosures, how to pick the right driver for you, and how to have a computer do some of the work for you.
These are a group of parameters outlined by A. N. Thiele, and later R. H. Small, which can completely describe the electrical and mechanical characteristics of a mid and low frequency driver operating in its pistonic region. These parameters are crucial for designing a quality subwoofer enclosure, be it for reference quality reproduction or for booming.
When it comes to mids and highs, efficiency (sensitivity) is a fairly good indicator of output differences at the same power level. When it comes to subwoofer performance, the driver's sensitivity is irrelevant unless you are also specifying a box volume.
An efficient sub requires a larger box to achieve equivalent extension to a less efficient sub. In a small box, the less efficient sub will actually be LOUDER at low frequencies at the SAME POWER as the more efficient sub.
Linear excursion is a very good indicator of ultimate output capability (given sufficient power to drive the speaker to that point.) To make sound you must move air; therefore, the more air you move, the more sound you make. When comparing two speakers of equal surface area, the one with greater excursion capability will play louder given sufficient power.
Only the order of the enclosure itself is shown here. The addition of a crossover network increases the order of the system by the order of the crossover. Example: If a First-Order, 6dB/Oct. crossover (single inductor in series with the speaker) is used with a Fourth Order enclosure, the total system is a fifth order. Note: Air volumes and ratios shown here may not be to scale. This is designed to provide order information only.
First Order
Infinite-Baffle or Free-Air
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Second Order Second Order
Acoustic- or Air-Suspension Isobaric* Acoustic-Suspension
or Sealed (Compound Loaded)
_______________________ _______________________
| | | _____|
| / | / /
| / | / /
| || | || ||
| || | || ||
| \ | \ \
| \ | \____\
|_______________________| |_______________________|
Fourth Order Fourth Order Fourth Order
Bass-Reflex or Passive Radiator Isobaric*
Vented or Ported Bass-Reflex Bass-Reflex
_______________ _______________ _______________
| | | | | ____ |
| / | / | / /
| / | / | / /
| || | || | || ||
| || | || | || ||
| \ | \ | \ \
| \ | \ | \____\
| | | | | |
| | | / | |
| | | / | |
| ____| | | | ____|
| | | |
| ____ | \ | ____
| | | \ | |
|_______________| |_______________| |_______________|
Fourth Order Fourth Order
Single-Reflex Bandpass Isobaric* Single-Reflex Bandpass
_________________ ____ _______________________ ____
| | | | | | | | | |
| / | | | | / \ | | |
| / | | / \ |
| || | | || || |
| || | | || || |
| \ | | \ / |
| \ | | \ / |
|_________|_______________| |_______________|_______________|
Fourth Order Fourth Order
Three Chamber Three Chamber Isobaric*
Single-Reflex Bandpass Single-Reflex Bandpass
____________ ____________ ______________ ______________
| | | | | | | | | | | |
| / | | \ | | / \ | | / \ |
| / \ | | / \ / \ |
| || || | | || || || || |
| || || | | || || || || |
| \ / | | \ / \ / |
| \ / | | \ / \ / |
|______|_____________|______| |_______|_______________|_______|
Fifth Order = Fourth Order Enclosure + First Order Crossover
= Third Order Enclosure + Second Order Crossover, etc.
Sixth Order Sixth Order
Dual-Reflex Bandpass Isobaric* Dual-Reflex Bandpass
____ _____________ ____ ____ ____________ ____
| | | | | | | | | | | | | |
| | | / | | | | | | / \ | | |
| | | / | | | | / \ |
| || | | || || |
| || | | || || |
| \ | | \ / |
| \ | | \ / |
|_______________|_____________| |______________|_____________|
Sixth Order
Three Chamber Quasi-Sixth Order
Dual-Reflex Bandpass Series-Tuned Bandpass
_ _________ _________ _ _________________ ____
| | | | | | | | | | | | | | |
| | | / | | \ | | | | / | | |
| / \ | | / |
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| || || | | || |
| \ / | | \ |
| \ / | | \ |
|________|_____________|________| | ____| |
| |
| ____ |
| | |
|___________|_____________|
Seventh Order = Sixth Order Enclosure + First Order Crossover, etc.
Quasi-Eighth Order
Series-Tuned Dual-Reflex Eighth Order
Bandpass Triple-Reflex Bandpass
_ _______________ _ ____________ _____________
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| | | / | | | | | | |
| / | | |
| || | | |
| || | | |
| \ | |____ _____________ ____|
| \ | | | | | | | |
| ____| | | | | / | | |
| | | / |
| ____ | | || |
|_____________|___________| | || |
| \ |
| \ |
|______________|______________|
* Isobaric or Coupled Pair (Iso-group) Variations:
A variety of configurations may be used in the isobaric loading
of any order enclosure. Physical and acoustic restrictions may
make one loading configuration preferable to another in a
particular enclosure.
Composite or Push-Pull Compound or Piggy-Back
or Face-to-Face Loading or Tunnel Loading
_________________ ___________________________
| | | ____|
| / \ | / /
| / \ | / /
| >>> || || >>> | >>> || || >>>
| >>> || || >>> | >>> || || >>>
| \ / | \ \
| \ / | \___\
|_________________| |___________________________|
Back-to-Back Loading Planar Loading
_________________________ ___________________________
| _________| | | |
| \ / | / |
| \ / | / |
| >>> || || >>> | || >>> |
| >>> || || >>> | || >>> |
| / \ | \ |
| /_______\ | \ |
|_________________________| |________________________| |
| |
/ |
/ |
|| <<< |
|| <<< |
\ |
>>> indicates direction of \ |
>>> simultaneous cone movement. |__|
This answer is not designed to tell you exactly what kind of enclosure to build, but rather to give an idea of the advantages and disadvantages to the simple configurations (Infinite baffle [1st order], Sealed [2nd order], Ported [4th order] and basic bandpass). Building and designing more complicated systems (order > 4) is not for the light at heart.
These instructions are for building a first order (sealed) subwoofer enclosure. Builing ported or bandpass boxes is more difficult, and those designs are less forgiving of mistakes. These instructions apply for all box designs, but be sure of the measurements before you make your cut. Building your own enclosure can save you a lot of money, but only if you don't need to buy all of your materials twice because of mistakes!
You will need:
Besides these materials you will need several tools:
Start by marking the cuts you need to make on your wood. Double check your math, and your measurements.
Use the table or radial arm saw to cut your wood. When you're done you should have six pieces of wood which fit together tightly to form a box.
At this point you will need to trace the cut out for your subwoofer onto the front of the box. Remember that if you have a 10 inch subwoofer you do NOT want a 10 inch cutout. The 10 inch measurement is from the outside of the mounting ring. The actual cutout diameter should be with your instructions. Transfer the proper sized circle onto the sub box and cut it out with the jig saw. If you have trouble starting cuts with a jig saw, drill a 1/2" hole in the wood inside the circle. You can drop your blade into the hole and then cut out to the edge of the circle and around.
After you have cut out your mounting hole you will need to cut out a square on one of the sides for your terminal cup. Transfer the proper size rectangle onto the wood and cut it out with the jig saw.
Now you are ready to start assembling the enclosure. Choose one of the ends, and one of the sides. Apply a bead of ahesive along the edge of the end piece. Affix it to the edge of the bottom piece. Flip it over (have a friend hold the other end and hold the end in place,) and screw the edge to the end. Use one screw at each corner and then one more screw about every 8 inches. Drill a pilot hole with your 1/8" drill bit, then drill a countersink with your countersinking bit. Finally, drive the screw in. Make sure that you don't strip the hole.
Repeat the above procedure with the other end. You should now have the two ends connected to one side. Affix the other three sides the same way.
Finally, you'll want to seal the insides of the box with silicone. Apply a bead of silicone across all the inside edges and around the terminal strip.
Allow the box to dry over night and then place your speaker into the hole. Screw it down and you're done!
Various enclosure design software is available via ftp from
The most popular program there is Perfect Box, which is in the file `perf.uu' (or `perf.zip').
Note that NO program can tell you what enclosure is best for YOUR car! The program does not take into consideration your space limitations, the type of car you drive, the type and number of midbass drivers you use, your musical preferences and the goals you have for your system. Many people follow (blindly) what a computer program says is "optimal," and end up unhappy with the results. Therefore, it is always a good idea to discuss a design you think looks good with a qualified installer or (even better) with the manufacturer.
For an overview of many programs and devices available for enclosure design, obtain the file `sahfsd01.doc' at the ftp.uu.net archive. The filename stands for "Software and Hardware for Speaker Design", and was added to the archive in June 1994 by an anonymous contributor.
An aperiodic membrane is one part of a type of subwoofer enclosure. It is an air-permeable sheet which has frequency-dependent acoustical resistance properties. The original design goes back to Naim, for use in home systems, but has been applied by several individuals and companies in car audio.
The completed system will be aperiodic, which means it will prove to be over-damped with a Q well below 0.7. In contrast, the most commonly used sealed enclosures have Qtc's in the range of 0.8 to 1.1 which are considered, by definition, to be underdamped. When improperly used, a high-Q system may have poor transient response, nasty peaks in frequency response, and high rates of roll-off. Aperiodic systems will feature excellent Aperiodic systems are characterized by better transient response, flatter frequency response and somewhat extended low frequency response.
Another benefit of the system is that you can pretty much choose whichever driver you'd like to use, as long as they are big. The Thiele/Small parameters (which would normally determine what kind of box would be used) are taken into consideration by the membrane designers so that the response is extended and overdamped, regardless of the characteristics of the driver.
Physically, the aperiodic membrane isn't for every car. It requires sealing the trunk from the passenger compartment in an air-tight manner, as well as sealing the trunk from the outside for best results. The drivers are then mounted into the baffle between the passenger compartment and the trunk, as would be standard in an infinite-baffle/free-air set-up. The aperiodic membrane is then placed either in front of the driver or behind the driver, depending on the type. When mounting behind the driver, the membrane is used as the rear-wall of a very small box which the driver sits in (as in Richard Clark's infamous Buick Grand National). So, in short, it's not suitable for trucks, jeeps, R/V's, or hatchbacks.
You should probably only get an aperiodic membrane if you've got money to burn, lots of amplifier power, some big subs, a sedan, a desire for trunk space, and no wish to boom. If your tastes lean towards bass-heavy booming, as opposed to well-recorded acoustic instruments, you're not going to be pleased with the result.
The following applies to all speakers in extremely cold conditions, but the question most often occurs in reference to subwoofers.
The suspension of the speakers will stiffen considerably at very cold temperatures (lower than 30 degrees F). So will certain cone materials which may become more brittle.
If a very cold speaker is played very hard there is a small potential for damage because more stress is placed on the cone's neck. The likelihood of damage is minimal for well-constructed and well-designed automotive speakers, however.
Thermally, the danger is minimal because the ambient temperature and the coil temperature are so low that it is highly unlikely that a coil will overheat and burn, despite limited movement and ventilation.
At temperatures between +20 degrees F and 0 degrees F, it is a good idea to play the system at a moderate level until the car's heater has warmed the vehicle interior. As the speakers warm up, they will play louder and lower signifying that their suspensions are warming up and returning to nominal compliance.
If the temperature is extremely cold (less than 0 degrees F), you should avoid playing the system at all until the vehicle interior is warm. This is to avoid stress fractures in the surround material (especially with rubber surrounds).
What you will need:
Before you start, find a large, clean, flat surface on which to set the box as you carpet it. Start by unrolling the carpet onto the surface, smoothing it out so that its flat, and setting the box on top of it edgewise. Also, make sure that you remove the speaker, any ports and terminal cups from the box.
The instructions on how to carpet the box are as follows:
Congratulations! You've just carpeted your box!
Magnet size is meaningless!
Every speaker will have an optimal BL (See section 4.1 What are "Thiele/Small parameters?" [CD, RDP],) product, the field strength in the air gap multiplied by the length of the voicecoil wire in the field.
If the BL product is too low, the speaker is electrically not very well damped (which will result in a woofer with a high Qts). A bump in frequency response and a level drop in midband efficiency may be the result. If the BL product is too high, the speaker is electrically overdamped (Low Qts woofer). A very high midband efficiency, but the driver starts to roll of early.
An high BL product can be achieved in a number of ways: increase field strength; or increase wire length in magnetic gap.
The increase in field strength is limited; so some manufacturers use very thin wire for the voice coil, as such they can achieve a high BL product with a low field strength (cheap magnet). Or they use an 8 layer voice coil... needless to say that electrical powerhandling will decrease enormously.
Long stroke woofers, having only a part of the voice coil in the air gap, need a very high field strength to achieve a high BL product. Often this means a big magnet as well...
Use magnet size as an indication, but as nothing more than that.
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