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Intro to Enclosures
Many things should be considered before building a speaker cabinet. For example, the type of music the customer listens to might determine whether you use a sealed or ported enclosure, or possibly a bandpass. The customer will need to have an idea of how much amplifier power and what size woofers he wants in the system.
The amount of space that a stereo system occupies must be known and approved during the design stage of that system. The salesman must make it known how much room will be sacrificed in order to get the performance level desired. The more sound a person wants, the more useable space must be given up. Midrange and tweeter drivers don't usually take up much space and are not considered at this time. Amplifiers, subwoofers, and to a certain extent the midbass drivers all need their own space in the interior of the vehicle. If woofer enclosures are desired, they can take up the most space of all. Larger woofers naturally require larger enclosures. In addition the larger woofers require more amplifier power to maximize them. This all takes up space.
One efficient way to get the customer the most performance is to measure that part of the car that he is willing to give up. With this total space in mind, subtract the room required for sufficient amplification, then subtract the thickness of the wood to be used. This will give you the net airspace avail¬able. If for example the net airspace came out to 3 cubic feet (85 liters) then you would be able to choose the woofer(s) that would work best in this situation. The choices would include a single C15a or F15a, two C10a or F10a's, or even four C8a or F8a's. Of course the Solobaric woofers could be used in much less airspace. The Solobaric woofers are normally re¬served for the customer that wants the best performance in the least amount of space with the understanding that more amplifier power is required.
An alternative to the enclosed woofer designs mentioned above would be to use either Freeair woofers on a baffle board or the self-contained Kicker Substations. While both of these alternatives take up a certain amount of space, they are a lot more compact, cost less, and take less time than the custom enclosure route.
TYPES OF ENCLOSURES
Infinite Baffle (Freeair)
The infinite baffle system is very simple and very easy to install. A baffle board is a wall the speaker is mounted to that separates the front and rear sound waves. The most important thing is to make sure the baffle board completely seals the front and rear areas. If the areas are not completely sealed, cancellation will occur and bass performance will be reduced drastically. The Kicker Freeair series drivers are designed specifically for this type of application.
The basic difference between our sealed box (Competition) and infinite baffle (Freeair) woofers is the design of the cone suspension. The tighter suspension of the freeair driver provides the cone motion control in an infinite baffle that would normally be provided by the small volume of trapped air in an acoustic suspension enclosure.
FREEAIR WOOFERS THROUGH PACKAGE TRAY
Advantages of Infinite Baffle ( Freeair)
Disadvantages of Infinite Baffle
The most basic and simple of all speaker enclosures is the sealed box or acoustic suspension design.
The acoustic suspension design has several advantages; it is easy to build, easy to tune and offers high power handling, tight response and extended low end output. Acoustic suspension enclosures produce lower bass because they roll off at 12 dB per/octave. Cone motion is better controlled at all frequencies because of the constant pressure on the back side of the cone, which enables you to run more power to the woofer. The Kicker Competition and Solobaric series are designed specifically for sealed enclosures.
Advantages of Sealed Enclosures
Disadvantages of Sealed Enclosures
A vented enclosure is not much more complex than a sealed box. It consists, basically, of a box with a hole in it. However, despite its simple design, vented boxes are considerably harder to get good performance from than sealed boxes - although many times the extra effort can be worth it.
The vent in the enclosure interacts with the volume of air in the cabinet and the driver to help increase output and reduce cone excursion at and around the tuning frequency. In fact, at box tuning, almost all the bass is produced by the vent - not the woofer.
The trick in building a vented box is to get the right size enclosure and the right size vent. You can't be too far off on either of these factors or your speaker's performance will suffer. In particular, using a too-small box or a too-high vent tuning frequency can eliminate bass instead of increasing it. Porting a sealed box that is too small usually does nothing to improve frequency response. The vent's placement within the enclosure is also important. You must leave at least the equivalent of the vent's diameter between the vent and any inside wall. For example, you would not place a vent with a 3" diameter within 3" of any wall. The same is true for clearance between the vent opening and the bottom of the enclosure.
Advantages of Vented Enclosures
Disadvantages of Vented Enclosures
A single reflex bandpass enclosure (sometimes called "fourth- or fifth-order") is a specialized cabinet design which uses a combination of sealed and vented box volumes to produce a shaped speaker response. We recommend Kicker Competition Series and Solobaric Series drivers for these enclosures.
Bandpass boxes are a critically tuned design and internal pressures can be very high. Small air leaks can seriously reduce performance, and panel flex can be much more of a problem than usual - particularly with enclosures using built-in acoustical gain.
Since all speaker output comes from the vent, air speed within the vent can be very high. This can produce some turbulence and noise (particularly with high gain enclosures), which can be reduced or eliminated by rounding the ends of the vent with a quarter-round router bit or a round file. The inside end of the vent must be at least one diameter away from any inside cabinet walls, or flow restriction will occur.
Single Reflex Bandpass Enclosure
Advantages of Bandpass Enclosures
Disadvantages of Bandpass Enclosures
Compound Loaded (Isobaric) Principle
Compound loading (a variation on the Isobaric principle) refers to the process of coupling two identical drivers together to work as one. Isobaric means constant pressure in reference to the air trapped between the two drivers. One of the attractive features of this design is that while the Fs and Qts remain the same for a pair of compound loaded drivers the Vas is cut in half when compared to one of the drivers by itself. When these values are plugged into an enclosure design formula the resulting box size is 50% smaller than that for one of the same drivers in the same style box.
There are three Compound loaded configurations possible: cone to cone (commonly called clamshell), cone to magnet, and the design that mounts two drivers magnet to magnet.
Compound loading can be applied to any of the enclosure designs described earlier in this section with the benefit of greatly reduced box size. Note that when using these configurations we have to power up two voice coils while the radiating cone area remains the same as a single driver. This results in a 3dB decrease in efficiency as compared to one driver with the same power.
For car audio, where the space savings is the main reason for using this design principle, the most logical version should be the cone to cone design because it is the most compact. When actually building this design a spacer with a minimum of 1/2" thickness must be added between all but the C18a drivers to prevent catastrophic failures.
The cone to magnet and magnet to magnet designs have a coupling chamber that is as compact as is possible between the drivers. This still adds to the overall size and negates the benefit of the smaller enclosure design.
When wiring the cone to cone or magnet to magnet designs it is necessary to wire the driver whose basket faces the listening environment electrically out of phase to ensure that the drivers move in the same direction at the same time.
Compound loaded enclosures that require porting, including Isovent and bandpasses, can be difficult or impractical to build. Because of small box volumes the length of a port may be too long to fit inside the enclosure. This can be solved in two manners. One is to allow some of the port to reside outside the box. The other option is to use 90 degree elbows inside the enclosure. Both these situations can cause other problems with wind noise and organ pipe resonances.
Building and Designing Enclosures
Building the Enclosure
When building an enclosure, the enclosure's walls should be as rigid as possible. Any flexing in the enclosure will drastically decrease your speakers' performance. Also, all of the joints and walls in a speaker enclosure should be airtight, including screw holes and wire holes. Any leaks or flexing will cause cancellation, resulting in reduced output.
Enclosures should be built with very dense and heavy wood. We recommend MDF (medium density fiberboard) or Medite (high density fiberboard), They are rigid, heavy and not porous like some particle boards. We recommend 3/4" (19mm) MDF although 1/2" (12.5mm) MDF is acceptable for woofers 8" and smaller.
Most enclosures are built for multiple drivers and require separate chambers for each driver. Dividers are a very important part of box building because they create strength in the box and provide an airtight seal between the speakers. Keep in mind that no two things are created equally (even speakers of the same size and model!), This will cause drivers in an open chamber to react differently, substantially reducing output and power handling. When assembling the box it is very important to glue all joints. Screws or staples should be placed approximately every 4" (10cm). Drywall screws work better if they are counter-sunk. Countersinking makes it easy to fill over the screw heads for paint or carpet, and improves the appearance of the enclosure.
A quality air stapler has been proven to be a good substitute for counter-sunk drywall screws. Use 1-1/2" (38mm) or 1-5/8" (41mm) staples at least every 3" (7.5cm) along every seam. Don't forget the wood glue. This is much faster and smoother than using screws.
Glue joints all the way across the wall to provide an airtight seal. We recommend Titebond or Elmer's Wood Glue.
It is always a good idea to use corner braces, also called glue blocks, on each joint in an enclosure. Corner braces are usually made from left-over enclosure wood and measure approximately 1" (2.5cm) wide. The braces should be glued and screwed or stapled to the walls and caulked on both edges where they meet the walls. Use a silicone caulk to ensure the airtight seal. Don't use "bathroom tile" type caulk, it won't do the job!
Not all corner braces will be the length of the wall they're attached to. For example, if a wall's length is 36" (1 m), but there is already a corner brace on the adjacent wall, we'd need to deduct one inch (2.5cm) so that the braces fit together - not overlap. Deduct two inches (5cm) from a brace's length if there are braces on both adjacent walls.
When adding braces to an enclosure always add the displacement of the extra wood to the gross box volume as it is designed.
Another type of brace, called a cross brace, should be used in any span that is 12" (30cm) or more to prevent panel vibration. The most common application will be from the front baffle to the rear wall and between the top and bottom walls. This type of brace is usually made of 3/4" x 2" wood. The brace will contact the enclosure only on its ends where it should be glued and screwed or stapled. Place the brace slightly off center for maximum rigidity. A perfectly centered cross brace can actually increase cabinet flex and resonance (at a higher, more audible frequency).
Designing General Enclosures
The fundamental Thiele-Small calculations can be performed using a scientific calculator and a little knowledge of algebra. However, it is important to note that the basic calculations have some factors averaged or removed for simplicity, and the answers they give are only approximate. Your best bet is to use known enclosure design data such as given here, or to use a computer program such as LEAP 4.5 along with our published driver specifications to assist you in designing enclosures.
When you have completed your enclosure, it is important to make sure the speaker is at least close to your design specs. Fori 00% certainty that everything is correct, you may want to measure the box tuning frequency for vented enclosures. If you did the calculations by hand or with a simple computer program (any program that requires only Qts, Vas, and Fs for enclosure performance calculations is simple), you will definitely want to measure tuning frequency because the vent dimensions given by the calculations could be off enough to reduce the speaker's performance. Be sure to measure the tuning with the enclosure in the vehicle, the acoustic environment of the speaker can also affect its tuning.
When designing an enclosure, it is best to follow what we call "The Design Sequence." This is a simple, three step process that can save you a lot of time and hair pulling!
The Design Sequence
Step One: Determine size of enclosure.
This is the easy part. Get a tape measure and get in the vehicle. Consult your customer on exactly how much space he or she is willing to forfeit for their system. Measure this area and write down the height, length and width dimensions in inches.
Now we'll learn how to calculate volume for a cabinet from the dimensions we just took. Let's say the space we have available is: 14" High x 41" Long x 14" Wide
The formula for figuring volume is pretty simple. Memorize it now, you'll be using it a lot!
Height x Length x Width = Total Cubic Inches
Total Cubic Inches / 1728 = Total Cubic Feet
Total Cubic Feet / # of Drivers = Total CubicFeet Per Driver
What is 1728 and where did that come from? 1728 is one cubic foot or 12 x 12 x 12. Dividing by this figure converts total cubic Inches into total cubic feet. You'll want to divide total cubic feet by the number of drivers to be installed in the enclo¬sure, usually two, to get the total cubic feet per driver. This is how the manufacturer usually lists specifications.
When calculating an enclosure's volume, you will work with EXTERNAL and INTERNAL dimensions. External dimensions are what you have after measuring the space available in the vehicle. Internal dimensions are what you'll want to go by when selecting a speaker for the enclosure. What's the difference? The thickness of the wood used to build the box. For example, if using 3/4" wood, you'd subtract double the thickness of the wood from each dimension to get internal dimensions.
Let's look at our example again and figure the internal dimensions using 3/ 4" wood.
3/4" + 3/4" = 1.5"
14"-1.5" = 12.5"
41"-1.5" = 39.5"
14"-1.5" = 12.5"
12.5x39.5x12.5 = 6171.88
INTERNAL cubic inches
6171.88/1728 = 3.57
INTERNAL cubic feet
3.57 / 2 drivers = 1.79 cu. ft. per driver
Step Two: Calculating Displacement
Displacement refers to the space used by things inside an enclosure that influence total volume and is mostly associated with the drivers in an enclosure. However, other factors will also influence an enclosure's total volume, like ports and bracing. To calculate exact enclosure volume, we'll need to consider port, bracing and speaker displacement.
Port Displacement: Calculating the amount of space taken by a port will test your memory of high school Geometry! The formula itself looks pretty simple: Area x Length = Volume. First you'll need to know the port's dimensions. For an example we'll use a 12" long port with a 2" diameter. Now we need to calculate the area of a circle the same size as the port, 2" in this case. (This is where Geometry comes in!) The area of a circle is the radius squared multiplied by "pi" or 3.14". Area of a Circle = r2 x 3.14 The radius of our circle is 1" (half of the diameter). 12x 3.14 = 3.14" Next, we'll multiply this by the port's length, 12". 12" x 3.14" = 37.68 cu. in. So, to get the accurate volume of the enclosure, we'd need to deduct 37.68 cu. in. from the total volume.
Brace Displacement: After figuring port displacement, brace displacement is relatively easy. Braces are discussed in detail a little later so trust us for now. We'll use a 1" x 1" x 20" brace for an example. All we do is multiply the dimensions together (1" x 1" x 20" = 20 cu. in.) and deduct this amount from the cabinet's total volume. Piece of cake! Remember to do this for all braces in the enclosure, there may be quite a few of them!
Driver Displacement: The driver also takes up air space inside the enclosure. If you use Kicker speakers, we've made calculating driver displacement real simple for you, just look at the chart on appendix page 25. The recommended enclosure volumes we give in the charts already have driver displacement deducted. If you use our speakers and go by that chart, you won't have to figure driver displacement. Let's get back to our example again. We currently havel .79 cu. ft. per driver before displacement. This size box might work for a 12" driver or a 10" driver. Let's calculate driver displacement now to where we are.
12" driver displacement = 0.0538 cu. ft. 1.79 - 0.0538 = 1.736 cu. ft. per 12" driver
10" driver displacement = 0.0334 cu. ft. 1.79 - 0.0334 = 1.757 cu. ft. per 10" driver
Now we'll look at braces. Two different types of braces are corner braces and cross braces. For this example, we are building a sealed enclosure in a simple rectangular box. We'll have twelve corner braces (one for each joint), and six cross braces (one for each wall).
We have eight corner braces that are 1"x 1"x 12.5". Each one uses 12.5" cu. in. of our enclosure's total volume, so eight of them use: 8 x 12.5" = 100 cu. in.
Four of our corner braces are 1" x 1" x 37.5". We deducted two inches from the length so the braces would meet instead of overlap the other corner braces. Each one of these use 37.5" cu. in. of our volume, so multiply this figure by four=4x 37.5" = 150 cu. in.
So all bracing combined uses 250 cu. in. Now we'll divide by 1728 to convert to cubic feet.
250 cu. in. / 1728 = 0.0289 cu. ft.
Now we go back to the enclosure volume figures we got after figuring driver displacement and deduct brace displacement:
12" driver 1.736 - 0.0289 = 1.7071 cu. ft.
10" driver 1.757 - 0.0289 = 1.7281 cu. ft.
Result - we use 12" Kicker Competition woofers in a sealed enclosure! Another possibility though, is the 10" Freeair driver in a ported enclosure. It can be quite a long process to figure all these different things, but trust us, going through all the trouble is worth it when you get done and have an enclosure that sounds awesome!
Let's say you're measuring a customer's vehicle for available space and it's basically unlimited in one direction. If two dimensions are known and the other is unset, we have another way to calculate volume for a specific speaker. For example, we'll say the customer wants to use our Competition 12" driver. We know that the recommended enclosure volume for a C-12 is 1.75 cu. ft., so for two it's 3.50 cu. ft. Our two known dimensions are 39.5" and 12.5" (internal). First we'll find the total cubic inches on our two known figures, just multiply them together.
39.5" x 12.5" = 493.75"
Next we need to figure the total cubic inches needed for two C-12's. All we do is multiply 3.50 cu. ft. (recommended for two C-12's) by 1728 to convert to inches.
Now we divide the total cubic inches needed (6048) by the cubic inches that we have already (493.75) to determine the missing dimension.
6048 / 493.75" = 12.25 inches for the width
To check this, multiply all three figures:
39.5" x 12.5" x 12.25" = 6048.44 cu. in.
6048.44 / 1728 = 3.50 cu. ft.
To figure enclosure volume on angled boxes, draw a diagram of your enclosure. It will help a lot to visualize what you're doing.
Using Figure A
17" High x 54" Long x 5" Top and 13" Bottom
Since the formula to determine enclosure volume does not allow for two different width dimensions (5" Top and 13" Bottom), we must find an average of these two figures.
To find the average, add the figures together (5 + 13) then divide by the number of figures added (2).
5"+ 13" = 18" 18"/2 = 9"
In essence, averaging the 5" width and 13" width gives us a rectangular box to work with instead of an angled one (note the "dotted line" enclosure). Now the formula for figuring volume works.
3.53 / 2 = 1.765 cu. ft per driver
To calculate internal volume, you must subtract the thickness of the wood. We're using 3/4" MDF again, so deduct 1.5" from each dimension.
54" - 1.5" = 52.5"
9"-1.5" = 7.5"
17"-1.5" = 15.5"
52.5" x 7.5" x 15.5" = 6103.13 cu. in.
6103.13 71728 = 3.53 cu. ft
Angled Enclosures With Risers
This type of enclosure (fig. B) is a little more difficult to work with than just an angled enclosure, but we'll help you through. Follow the calculations below for volume on an angled enclosure with a riser.
Using Figure C.
Dimensions: 17" High x 44" Long x 5" Wide (Top) and 13" Wide (Bottom) with a 4" riser.
First, make the box into a rectangle like we did before by averaging the top and bottom width measurements:
5 + 13=18 18/2 = 9
Instead of using the entire height dimension, deduct the height of the riser, 4" for this example.
17" - 4" = 13" High
So the external dimensions for the first part are (fig. C):
13" High x 44" Long x 9" Wide
We'll go ahead and figure the volume of this enclosure (using internal dimensions). Subtract only one thickness of wood from this height.
12.25 x 42.5 x 7.5 = 3904.68 cu. in.
3904.68 / 1728 = 2.25 cu. ft.
2.26 cu. ft. 12 = 1.13 cu. ft. per driver
Notice that there is a 4"x44"x13" enclosure left over. This is just another airspace that we'll figure volume for and add to the first part. (Use internal dimensions!) Again, subtract only one thickness of wood from this height.
3.25 x 42.5 x 11.5 = 1588.43 cu. in.
1588.43 / 1728 = 0.92 cu. ft.
0.92 cu. ft. / 2 = 0.46 cu. ft. per driver
Now, add 0.46 cu. ft. to the first figure:
0.46 + 1.13 = 1.59 cu. ft. total per driver This is your net internal airspace for each side of this enclosure.
Box Building Hints
All the cubic feet numbers given in the supplied charts include the displacement of the woofer. For the ported boxes, the displacement of the port must be added to the final design. It will be impractical to use round ports for these designs. The rectangular port information given will yield the best results.
Always use 3/4" or thicker MDF and make sure all the joints are secure and well sealed. The peak pressure in a ported box can exceed that of a sealed enclosure. All of these designs need some internal bracing. Be sure to add 2"x2" to 3"x3" triangle braces between each of the larger unsupported panels. Kicker recommends using a good grade of wood glue and silicone sealer for an airtight box.
Note:If you prefer an ultra-smooth bass response, you should loosely fill your ported Solo-Baric Enclosure with polyfil. If you do so, the entrance to the port (inside the box) must be covered with hardware cloth, chicken wire, or expanded metal to prevent the polyfil from being blown out through the port. Use of polyfil will slightly decrease efficiency, but will deepen and extend low bass response.
Do not install a ported box with the port against a solid surface. The port opening must remain unobstructed. Use the smallest dimension of the rectangular port as the minimum amount of space required between the port and any surface to insure unrestricted airflow.
If you would like to use a vented enclosure, but the box designs we provide you with (in this manual) do not fit because of width or depth, the designs can be modified. The shape of the enclosure is not vital, but The Volume Is. The volume, of the design you choose, must stay the same. The following diagrams provide you with some help to insure your enclosure is built correctly.
If you are going to bend the port at 90° you will need to add 1/2 of the ports height to the length! See Below.
Hport = 3"
Lport = 20"
Since Hport is 3" you need to add 1.5"( 1/2 Of Hport) tO Lport. This means that L1 + L2 = 21.5".
Always measure L1 and L2 down the center to get an accurate measurement!
Here are a couple more examples of the different shape enclosures you can build. The woofer can be mounted on the same side as the port or the back side of the enclosure can be slanted to fit up against your back seat.. On the cut sheets we provide, change the dimensions to accommodate the woofer and the vent on the same side. Make sure the internal volume does not change!
Sometimes an installer needs to calculate the volume of some geometric shape or units of measure. Below are some formulas that should help out.
Triangle Area = 0.5x (Base) x (Height)
Circle Area = (Radius) x (Radius) x 3.1415
Circle Area = (Radius) x (Radius) x 3.1415
1 inch = 25.4 mm
1 mm = 0.0394 inches
1 liter = 0.0353 cubic feet
1 cubic foot = 28.32 liters
1 gallon = 0.134 cubic feet
1 cubic foot = 7.48 gallons
1 cubic foot = 1728 cubic inches
1 cubic inch = 0.00433 cubic feet
Volume (Cubic inches) = (Length) x (Width) x (Height)
milli = 0.001 micro= 0.000001 kilo = 1000 Mega = 1,000,000
Outside Area (1/4 in walls)
0.785 sq in
1.767 sq in
0.89 x 0.89 in
1.767 sq in
3.142 sq in
1.33 x 1.33 in
3.142 sq in
4.909 sq in
1.77 x 1.77 in
7.069 sq in
9.621 sq in
2.66 x 2.66 in
12.566 sq in
15.904 sq in
3.54 x 3.54 in
19.635 sq in
27.758 sq in
4.43 x 4.43 in
28.274 sq in
33.183 sq in
5.32 x 5.32 in
50.265 sq in
56.745 sq in
7.09 x 7.09 in