Properly sealing a subwoofer box is important because sealed box enclosures reproduce low frequencies more accurately. This is because the air inside the box acts as a shock absorber, allowing the subwoofer to move back and forth with more control.
In this article, we will be showing you how to seal a subwoofer box or speaker box.
You will hear a lot of recommendations on how you should go about sealing your subwoofer box and making it airtight. This is very important for a loud sealed subwoofer or speaker box. You’ll hear everything from using wood glue to epoxy resins.
We should also mention that instead of building a subwoofer box, you could also get a subwoofer tube which is cheaper and generally smaller, but they sound as great. If you’re interested, you can read more about subwoofer bass tubes vs subwoofer box.
The fact is, you can seal your subwoofer box with a wide variety of materials including silicone, Liquid Nails, Gorilla Glue, epoxy, and more. The most important thing is to ensure the box cuts are precise and air gaps are kept to a minimum.
However, it is also important that you don’t just go out and use any old material or method to sell your subwoofer box.
This is especially true considering that most speaker builders/hobbyists are woodworkers, so building a perfectly sealed sub box isn’t second nature to them.
How To Seal Subwoofer Box Step-By-Step Details
1. Make Sure The Cuts Are Precise
As we already mentioned the type of sealant you use is as important as the precision of your cuts.
In fact, if your cuts are precise enough, meaning they are clean and straight, you may even get away with not using any sealant but simple Elmer’s glue and a few well-placed screws.
The cleaner your cuts are, the stronger the sealed seams will be. All of the panels should fit snugly together.
2. Get A Good Subwoofer Sealant
The second step to sealing a subwoofer box is finding an appropriate sealant or adhesive compound. For this purpose, many people use silicone since it’s a common household compound and is readily available.
However, not everyone has silicone on hand. In this case, there are many other sealants that you could use.
Each has its own advantages and disadvantages. Here’s a rundown of different subwoofer sealants along with their benefits and best use case:
Silicone is a readily available and simple adhesive that will work pretty well if your woodcuts are precise enough. However, if the woodcuts are uneven and leave a lot of air space, you may have a problem because silicone does not expand like polyurethane-based construction adhesives.
However, silicone does provide an enormous advantage in terms of strength. When dry, silicone will turn into 100% rubber and is flexible so it won’t crack.
Follow the curing directions for silicone which usually requires 24 hours before mounting your subwoofer. In fact, some people leave it to cure for several days.
The disadvantage of using silicone is that the vapors of silicone can cause damage to the sub if you install the sub while the silicone is still wet and drying.
Also, try to get acrylic latex with silicone, that’s some seriously strong stuff! In addition, this will emit little to no fumes. Finally, it isn’t a good idea for you if you go ‘gloveless’ so be careful.
2. Gorilla Glue (Elmer’s, Titebond, PVA)
Gorilla glue is a polyurethane-based construction adhesive. The benefit of this type of adhesive is that they expand 3-4 times the application as they cure to fill all gaps to create a superior bond.
If your cuts are clean and straight, wood glue is much easier to work with and absolutely strong.
Keep in mind, however, Gorilla Glue is not made to be a gap-filling glue, so you need to apply enough to get the job done.
This means the cuts of the MDF have to be good, wood glue is not designed to fill gaps any bigger than 1/8 of an inch but when dry, the bond will be stronger than the MDF itself.
3. Caulking Gun
Caulk is a polyurethane-based construction adhesive. Again the benefit is that it expands as it cures to fill all gaps. In terms of caulking, you can use acrylic latex caulking.
Some people may also use caulk with silicone, but it’s more expensive and sticky. If you have ever heard the term acrylic subwoofer boxes, this is what they are talking about. You can even use acoustic sealant caulk for this purpose if you don’t have acrylic.
4. Liquid Nails
When we talk about enclosure adhesives, a liquid nail solution is almost always suggested. This is because it is a thicker substance that can fill in minor variations in the surfaces while maintaining the enclosure strength.
This makes it simple and easy to use, so it’s great for a beginner.
So, liquid nails is best used in instances in which your cuts are less than perfect as it will fill gaps being a bit thicker of a substance.
In terms of strength, it bonds about as well as wood glue. Moreover, it begins to dry quickly.
5. PL Premium Construction Adhesive
These are polyurethane-based, moisture-curing adhesive that uses caulk to hold the seams together.
3. Seal Inside The Box
When we talk about sealing subwoofer boxes, we don’t mean you should just seal the seams. You should also sell the inside surfaces of the box.
This is because the wood itself is going to be porous to some extent, especially if you use MDF. You should seal the inside of the box with some kind of water seal.
As an example, you might consider using polyseamseal all-purpose adhesive caulk, its water-based, uses PVA (meaning white glue), and washes up with water.
On the other hand, you may also want to add some weight damped the enclosure and seal the MDF. In that case, you can use Boro-Silicate paste or some type of fiberglass resin.
4. Seal All Extra Holes
There may be some extra holes in your subwoofer through which air may escape. For example, small gaps around the speakers and around the speaker terminals on the back of the box.
In such a case, you should use a gasket which is a rubber/plastic ring that goes around the hole.
5. Ensure All Gaps Are Filled
Ensuring all gaps are filled is important. If you used a polyurethane-based construction adhesive, for example, it should foams up and fill the seams quickly.
A quick and easy way to fill the old holes and gaps is to use epoxy putty. If at this point, you still have gaps, then you can redrill and use new screws to get a tighter seal.
6. Seal All Seams
Now it’s time to use whatever subwoofer sealant you chose to seal up all the seams. Lay the sealant heavily on all seams using the sealant or glue.
Cover all internal seams heavily with the sealant.
7. Clamp and Let The Sealant Cure
It’s time to let the sealant cure. Use clamps to hold the different parts of the subwoofer box together.
It is important to remember that different subwoofer sealants will take different amounts of time to cure.
This is very important because some sealant fumes for example silicone can damage the driver. As an example, the normal cure time for silicone is 24 hours, but many people let it sit longer just to be sure.
Check the cure time for the sealant you are using and allow the sub to set and cure.
8. Sand Away Excess Sealant and Add An Aesthetic Finish
Now that you have gathered the seams with sealant, it may not be the most pleasing result. You can now use some sort of compound to give a better finish.
Here are a few:
1. Woof killer and wood putty: Wood filler and putty are adhesive compounds used to fix defects in wood. They are not the strongest compounds, but they can work if it’s all you have.
Note that wood filler will not strengthen a weak spot in the box, but it helps in terms of filling small voids or as a finish over an uglier sealant.
Keep in mind that wood filler is usually water-based, whereas wood putty is most often oil-based.
2. Bondo: Make sure you are not sculpting with the Bondo since it will crack. Instead, use it as a final finishing touch to make the subwoofer seams look better.
Home Depot and other big box stores sell Bondo in gallons because it is such a great wood filler. When using Bondo, only mix a little bit at a time unless you are going to work super fast because it gets hard very fast.
Bondo is great because it forms a permanent, nonflexible bond with the material that can then be sanded and painted.
Keep in mind that there are two different types of bonds. There is one type that is made of wood and the other for automotive use. In general, you can use either to seal your subwoofer box.
There are two types, one that’s made of wood and one that is made for automotive uses. Either will work, but the automotive is a little easier to work with.
Chisel and Sand Away Excess Filler
First, use a sharp chisel to remove excess sealant that oozes and dries onto the exterior of the enclosure.
After applying the additional fillers, allow it to dry, and then sand down the excess. This way, you can achieve a smooth finish.
The next step is to add an aesthetic finish with varnish or whatever you chose to use. Many people use paint, carpet or vinyl.
9. Screw Down The Box
To tighten the box and make it truly airtight, you need some kind of mechanical fasteners like screws, nails, or staples.
Here is an example, get a countersink pilot bit for the holes, and use 1 5/8″ drywall screw every six inches.
However, as we said before, let the box sit and cure before you screw it. This is especially true if you will be using polyurethane adhesives as they ooze a lot.
If you aren’t careful and use weak wood, the screws can actually damage the wood. However, an easy way to avoid such issues with the plywood is to predrill and countersink the holes and get good quality plywood to begin with.
When You Shouldn’t Use Screws
We already said you can damage the box if you aren’t careful with the screws or use poor-quality wood.
For example, if you use cheap-grade plywood, ply separation could occur. There are two things you need to keep in mind to avoid this.
For one, you need to pre-drill pilot holes. secondly, you use enough screws depending on the wood. For example, with 3/4 inch plywood make sure there are no less than 7 plies.
Also, if aesthetics is most important to you, then you may want to avoid screws because it can be quite difficult to cover them up unless you’re using veneer.
Subwoofer Sealant Silicone Alternatives
We already mentioned a few compounds that can be used to seal your subwoofer, including the popular silicone. However, you may not have any of those on hand.
In that case, here are a few handy DIY subwoofer sealants that can be used instead of silicone and other standard adhesives used to seal subwoofer boxes:
Would you believe people have used regular tile grout to seal subwoofer cabinets? Remember, this is pretty hard stuff, so when the grout dries, you may not even be able to remove it with a chisel!
So, be prepared for some pretty unsightly edged unless you were very careful and neat when applying the grout. You will probably have to sand it down.
There is a superglue called “Goope” that glues and seals anything. in fact, it is one of the strongest, most flexible all-purpose adhesives ever created. It will make your enclosure super airtight.
Firstly, we warn against the use of spackle because it may very well turn to dust under vibration. However, if you must use it, just smear in some caulk and smooth over it so that it will stay put.
Do You Need To Seal Your Subwoofer Box?
Do you need to seal your subwoofer box?
Yes, you do, sealing your subwoofer box is very important.
If there are still gaps after the enclosure is assembled, one may want to try a new enclosure. Every single panel must fit perfectly and snuggly together.
Even if your subwoofer box is cut and the seams glued, it’s still a good idea to add an extra layer of protection.
Should I Seal My Subwoofer?
An appropriately designed sealed subwoofer will typically exhibit less phase rotation, lower group delay, and reduced ringing in the time domain. Sealed cabinet subwoofers are generally more accurate in frequency response and better at compellingly rendering instrumentals.
Enclosures should be airtight and so you need to use a proper sealant (of which there are many) to completely seal the enclosure along with screwing the panels in place so that the subwoofer box is completely airtight.
In general, there is very little difference in sealants. Pretty much any kind of polyurethane adhesives or caulking will work.