A subwoofer box must be enclosed in soundproofing foam in order to ensure that there are no gaps or holes in the box. This will prevent the sound waves from escaping outside the box. It is best to use wood when assembling your box, ensuring each piece is glued together tightly. Make sure to cover the insides of the box with soundproofing foam. This foam needs to be thick enough to close up all gaps and will also help with any vibrations that may occur.
In this post, Hooke Audio will guide you How to Build a Subwoofer box.
Basic Steps To Make a Subwoofer Box
Building a car subwoofer box, you need to consider several factors that will affect its design:
- Define where in the car you will install the box.
- Define the shape of the box, whether it will be standard or customized to fit in the vehicle’s body.
- Define the number of speakers and their size that will determine the volume of the box.
- Choose the type of box: sealed, vented, or bandpass.
When you have the above information, you need to measure how much space you have in the car, determining any further adjustments to the size.
Make sure you consider the suitable material, which in most cases will be either fiberboard or plywood. Besides, in some subwoofers, you will need a damping material like fiberglass, and if will decide to make a vented enclosure, you will need a plastic port.
How to Calculate Subwoofer Box Size?
The most important part of any project is making accurate calculations. It is essential that you put your ideas on paper. This is where you can make any changes and without incurring any costs.
Before you begin designing the subwoofer boxes, make sure you know how much space you have in your car. This is an important step that you should not skip. The last thing you want to do is make the box too tall for your trunk by a half-inch.
First, check the volume recommendation of your speaker.
The volume of the speaker type will determine the box’s size. You can adjust the box’s shape and length, but the volume of your subwoofer box cannot be altered. It is fixed with tight tolerances.
The manufacturer’s manual or the speaker’s paperwork can help you determine the recommended volume. Here is an example of the specifications for JL speakers 10W1-4, 10W1-8 subwoofers. Let’s take this as an example and use it for our next steps.
This specification provides basic dimensions for both boxes as well as details about the material thickness. It is 0.75″ or 0.625″, in our case. This is the minimum.
For walls smaller than 0.625 inches, it is best to use thicker wood. This will cause the enclosure to be unstable and may start rattling.
Direct factory recommendations will have the best results.
The dimensions listed in the specification do not have to be exact. The manufacturer recommends 18’’ x 11’’ x 10.25’’. You can adjust the dimensions to fit your car better, but the volume of the sealed box must not exceed 0.75 cu ft.
To compensate for volume loss, you can either increase the width or height of the box to reduce its depth. You can adjust the size of the box to compensate for speaker size limits.
Here are some examples of combinations for external boxes sizes that you can make up to 0.75ft3 with material 0.75″.
Width – Height – Depth:
- 18″ – 11″ – 10.25″
- 17.5″ – 14″ – 8″
- 12.5″ – 12.5″ – 12.25″
What is the Volume of a Cubic Feet?
Converting cubic feet into inches gives exactly 1728. This constant number is not subject to change. This means that 12” x12″ x12’’ = 1728 cubic inches per cubic foot.
The given box volume in our example is 0.75 cubic feet and 1296 cubic inches.
Remember to use the number 1728 as the starting point when making a subwoofer box.
Let’s say you want to put a subwoofer 10″ in a square box that is as close as possible to the frame’s diameter.
Can the subwoofer be placed in this box?
You can see that the mounting hole diameter is 9.125 inches. Therefore, you will need to multiply this value by 2 x the wall thickness.
9.125″ + 2 x 0.75″ = 10.625″
As you can see, the speaker won’t fit in a 10″ x 10″ enclosure. If this is your limit, this speaker cannot be used in your car. To make things easier, let’s make the smallest box 11”.
How deep is the 11’x11” box?
The following formula can be used to calculate the inner depth of your box:
1296 / ((11″ – 0.75″)x (11″ – 0.75″) = 12.33″, this is your inner depth.
You will need to multiply the external box depth by 2 x the wall thickness.
12.33″ + 2 x 0.75 ” = 13.83″s
You can increase depth up to 14″. This will not impact sound quality and will make it easier to do further calculations.
You must also add 2 inches to the depth for the baffle on which you will mount the subwoofer. So in this example, the total box depth is 16″.
For powerful subwoofers mounted in boxes made from thin materials, a baffle or wall with double thickness should only be used on the top of the box.
Once you know the dimensions of your subwoofer box,
11″ (width) x 11″ (height) x 16″ (depth)
Now it is time to calculate all six elements’ actual sizes.
Front and back walls will measure 11” x11”
Sidewalls require you to subtract the material thickness and adjust accordingly.
2 pcs 11’’ x (16’’ – 0.75’’ – 2.75’’) = 11’’ x 12.5’’
2 pcs (11″- 2 x 0.75″) + (16″- 0.75″- 2.75″) = 9.5″ x 12.5″
This is how you can calculate the volume of a sealed container.
You can make a box with custom shapes, or vent with multiple ports. If you are interested in making a box, please create an example project on paper. This will help you to understand the size relationships.
You may also need design software. For the fast design of different subwoofer boxes, I use WinISD (the link opens in the next window).
To receive a box design that fits all dimensions, you will need to fill out the following information: box type, subwoofer driver.
Once you have the dimensions for your subwoofer walls, you can transfer them to the material.
What is the best material needed?
You must ensure that your subwoofer box is as rigid as possible, without any flexing when you construct it.
It shouldn’t be an issue with thinner material for small sealed boxes. However, it can pose more problems when you make a vented box or bandpass.
3/4″ or 0.75 inches is the recommended thickness for this material. You can use 1/2 inch or 5/6 inches thick wood for smaller subwoofers, such as 6.5″ or 8″. However, I prefer 3/4 inch.
You might be wondering what the best material is for subwoofer boxes. There are many options, so let’s take a look at the most popular.
MDF (Medium Density Fiberboard)
MDF is the most common material used for standard enclosures. This wood is extremely durable and dense, which helps to improve the sound quality.
It is very easy to cut and assemble, which I find my favorite. MDF is ideal for areas with high humidity and intense winters because it doesn’t warp or expand. MDF is also sound-disruptive because it is thick.
MDF’s one major disadvantage is its weight. It doesn’t matter for smaller boxes unless you have to carry them around every day. But it is critical for multi-driver constructions.
Subwoofers that have 2 or 3 large drivers can weigh more than 200lb. This article contains a weight overview for several types of speakers and boxes.
Another popular material for subwoofer boxes is plywood. Plywood is lighter than MDF and strong enough to not rattle. Make sure plywood is free from any surface defects that could cause vibrations and rattling of the walls.
Fiberglass is a great choice for lightweight constructions. It can also be used to create complex and customized shapes.
How to build a subwoofer box
Once you have your design and all the materials, it’s time to begin making the actual box.
You will need strong glue, screws, and caulk to put together a subwoofer box. I’m using Elmer’s Professional and have had excellent results with MDF. It’s strong and fills in small gaps with an excellent sealing agent.
However, glue is not sufficient. Screws are required to make the box strong. However, screws should not be used for too long. Two inches will suffice. I use Hillman fasteners and they work well with all wall thicknesses.
Subwoofer boxes should not be fitted with nails. They will eventually become loose due to vibrations.
You should also place braces between walls. You should also place braces between the walls. They add stability to your box, especially if you have multiple drivers.
Use 2”x2” wood strips to glue between the walls. They are best for large boxes but I use them all the time.
Let’s get started by making the box.
Draw all Subwoofer Walls on MDF
All external measurements should be taken for the MDF box panels. There should be 7 pieces total, 6 walls, and 1 extra panel to mount the driver. Based on our previous calculation, you’ll have:
- 3 psc – 11’’ x 11’’ – tops and back
- 2 pcs – 11″ x 12.5″ – sidewalls
- 2 pcs – 9.5″x12.5″ – sidewalls
All pieces can be cut using a table saw
You can cut all panels with a table saw. You don’t need a table saw to make straight cuts. I don’t have a table saw and use this Makita circular saw with a carbide triple blade. It works great with MDF.
All cuts must be square. You will get a lot of dust from cutting MDF. If you’re working outside, it is worth wearing a mask. Make sure to protect your eyes with glasses.
Join Two Front Panels 11” X11” by Gluing
The front wall of your subwoofer box will be made by connecting two 11’’ x 11’’ panels and doubling the thickness.
Cover the entire panel with strong wood glue. The Franklin International 5005 Titebond II Premium Wood Glue has been my favorite and provides a strong connection for larger areas.
Don’t leave any gaps or open edges. This could lead to rattling. Keep the pieces together until dry with a few sheet metal screws.
It is sufficient to leave it outside for at least two hours before I cut the mounting hole.
Mark the center point, and then cut the mounting hole
Once dried, locate a central point on the glued panel. Mark a 9.5″ circle around it. To use your subwoofer’s hole template, you should have one. You can also use a compass to mark if you don’t have a template.
Make a small hole in the center of the circle. You should make sure the hole is large enough to accommodate the standard jigsaw knife. I use a 1/2″ drill to fit the blades.
Make a mounting hole in the doubled panel. A jigsaw is the best tool for this task. Follow the circle line.
For a subwoofer terminal, make a small hole in your back panel
You will need to make a hole in your back panel. You will place the subwoofer terminal in this hole. It will vary depending on which terminal model you have.
This saves time and allows me to wait for the panels to dry before I mount the terminal. Once you have the terminal hole ready, don’t mount it yet. You will cover the box with carpet after you finish covering it.
All panels should be mounted together
It is now time to attach all the panels together. I will start with the back of the box and then move on to the small walls. End result: I cover all walls with a doubled panel front.
Make sure to drill holes near the edges of the panels before you attach the screws to them. MDF tends to split if you screw it too close together.
I am drilling holes with 5/64’s drills. The spacing between each other is 5” to 6″.
Apply a thin coating of glue to all mounting surfaces of the panels
Once you have predrilled all holes, glue all mounting surfaces. You should seal all gaps properly. It is better to use more glue than less for the subwoofer box. After fastening the enclosure, you can remove any excess glue.
Use screws to fasten walls together
Screw the entire box together using pre-drilled holes. For the sidewalls and the back of the box, I use #6×2” or #7×2” screws. However, for the front of my box due to its 1.5″ thickness, I use #3”. This is the most important part of the subwoofer box. It should not be 2”. MDF requires that the screws used are longer than the others.
This was the last step in building a box. As long as you’re happy with the final result, it was a good job. I will leave the box to dry for a couple of hours after this step. These are the last steps to finish the box.
All gaps between wooden panels should be sealed
After the glue has dried completely, I seal all the internal seals using silicone caulk. This will seal any gaps left in the glue.
I cover all the corners and leave the box to dry completely until the next day. Some silicones can take up to 48 hours to dry. The next step is to carpet the subwoofer box. This will only be done from the outside.
How to Use a Carpet Subwoofer Box
I use a razor blade, spray adhesive, and a ruler to cover a subwoofer box. You can finish your subwoofer box with different materials by reading this article by Crutchfield.
Measure the carpet to determine the right size
Precutting the carpet to the size of the box is the first step.
In this case, I took a piece of carpet measuring 43″ x 70″, and it will cover the entire box.
The whole carpet can be used, but I don’t like it too big on my table. So I use this formula to calculate how much carpet I actually need.
Carpet width is the front width plus the length sidewalls
11″ + 2×16″ = 43″
Carpet length is the distance from the front to the box’s perimeter, plus one side for overlap.
11″ + 2 x 16″ + 11″ + 16″ = 70″
The carpet should be laid on the enclosure.
Let’s now carpet the box once you have your carpet ready.
It is always better to see carpeting in person, so the video below will show you step-by-step the entire process.
Place the wire terminal into the mounting hole
Once you have your box almost finished, it is time to place a subwoofer terminal into the hole. To prevent air leakage, I use 1/2-inch screws and silicone from the inside.
Connect the wire terminal to the subwoofer
Next, connect a subwoofer cable to the connector inside the enclosure. Make sure the terminal is properly sealed against the back wall. It could become the weakest part of the sealed speaker, and ruin the entire project. You should also remember to keep the wire as short and straight as possible. The wire should not rattle in the box due to vibrations.
Polyfill the enclosure’s interior
I have wire in the box and am filling it with a . I’m not going to fill the entire box, but just the sides and back with spray glue so that the driver can breathe and won’t overheat.
A bass box is filled with enough wire to ensure that the loose wire will not rub against the walls. However, the best thing I noticed was the sound. The bass is deeper because polyfill absorbs sound.
Test it by mounting a subwoofer inside the enclosure
Once the box has been sealed and connected to the speaker, mount it to the enclosure and test the subwoofer.
It is worth putting a rubber gasket at the bottom of your speaker before you screw it into the box. This will prevent air from leaking out of the enclosure.
Install a subwoofer in the mounting hole. Make sure that there is no gasket sticking out. 1-inch screws are used to attach a subwoofer. Because the thickness of the front panel is 1.5 inches, it is best to use shorter screws.
Install a bass box in your car
The radio will turn on when you take the box to your car. Plug a speaker wire into the terminal. Don’t increase the volume too much at the beginning.
Although you may need to adjust the crossover and amplifier filters to achieve the best results, I’m sure you’ll be happy with the end result if you pay attention to every detail.