A sealed box design is a type of enclosure that is used to get the most accurate and precise bass response from your car subwoofer. The advantage this provides over a vented ported box is cleaner sound that has a flat bass response throughout the frequency range below 80HZ. People these days take a ported box over a sealed any day because its louder, making it a great choice if you listen to lots of bass heavy songs such as rap and hiphop. If you want to make your sealed subwoofer box sound more better and louder, there are a few things that you can do to enhance audioable listening. When building a sealed box for our customers, we apply the following techniques to ensure the best possible sound they can get. But remember these tips only go so far if the box you are using is not built to spec and has less internal volume space than what the spec of the speaker requires. You will only notice so much of a difference compared to applying these tips with a box that is built to spec interms of internal volume and strong supportive bracing.
1) Seal Seal Seal! Air leaks are very prone to causing a loss in sound pressure level. Sealing up the box inside will provide an air tight seal stopping your subwoofer to sound bad at high volume. Now interms of how to seal a subwoofer box, the best way is to run the insides with wood glue. If your box also has a plastic terminal cup for speaker wire connections to the box to the amp, go around it inside the box with glue. Lots of air can escape out of the sides of the terminal cup, this can make up to 2 DB difference. Remember to allow it to try before putting the subwoofer in as you can damage the cone and spider.
2) Polyfill. This is the white stuff you find inside pillows and bed blankets. It is used in a subwoofer box to trick the speaker into thinking its placed inside a much larger box. This results in deeper bass and gets rid of the peak in the 50-80 HZ area. The bass will be more depth full with your music and not so boomy like a cheap halfords sub. Interms of how much polyfil you need per cubic foot, its hard to say but its trial and error really. Interms where to buy polyfil from it shouldnt be a problem if you shop online. However, if you need it there an then that you can't wait for delivery, you can go to a shop and purchase a couple of pillows. Cut them open with a scissors remove the polyfill stuffing. The best way to insert it into the box is using carpet glue adhesive spray inside the box to stick it on the inside walls of the enclosure. You could also staple it on depending on what works the best for you the results will work out the same once you have the right amount.
3) Use thicker speaker wire. We have seen electrical extension cord used as speaker wire inside the sub box to the terminal cup. This doesn't work so well when you are sending 1000 watts rms to it, but its ok for a cheap budget ghetto system because you got to think about its better than having no bass at all. The copper strands inside the wire can't take the current and they will as a result produce a poor quality sound. What gauge speaker wire for a subwoofer depends on how much wattage you are using. To be on the safe and make your system future proof for later on upgrades its best to use 12 gauge speaker wire that is made from oxygen free copper.
4) Setup your car amplifier correctly. This also contributes towards make a sealed subwoofer box sound better and louder. You need to enable the low pass filter LPF and set it to around 60-80HZ this will make it only play bass and stop vocals treble going to it. Play around with it see what works best for your car, since there are many factors such as cabin gain that can affect how the bass sounds inside the car. Also you need to tune the gain properly with the headunit to prevent no distortion at high volumes.
5) Screws! Screws hold down the subwoofer into the box and terminal cup. You need to ensure that each screw is fully tighten with a hand screwdriver to ensure maximum seal. We have seen some customers installs with a few screws missing holding the sub in place. This causes noticeable air leaks at high volumes. So go over the screws, check for any missing and tighten them to their best. A tip that we use to tighten the screws is to place your finger over the rubber edge surround of the speaker. This will protect the screwdriver from making a rip into the speaker if it does slip when applying strong pressure to make a good air tight seal for the best bass.
6) Bracing. Internal bracing is very important because it stops your enclosure from box flex. It can help provide more of a rugged structure inside the box. The best subwoofer bracing techniques is to use a wooden dowel and place two of them one of the left and the other on the right inside the box. If your box is already made you can hold them in place using glue. This can make a big difference if you have got a subwoofer with big magnet motor force. The sound will be less sloppy and will hit harder with authority.
With this expert level car audio advice to help you make your sealed subwoofer box sound louder and better, you will get a big difference in spl. Sealed boxes can get loud too and sound if not better than ported box without taking up half the space in the trunk. I think we covered just about everything here today, if you have questions about your car audio system then send us an quick enquiry. These tips can also work best for ported subwoofer boxes to get hard hitting deep bass without getting a bigger amp. 
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