If you are wondering how to add a port to a sealed sub box using a PVC pipe to make it louder then you have come to the right place. We have all been in that situation, where we have a prefab sealed box and want to try out how a ported box sounds, but don't want to spend money or have the time to build a custom build subwoofer enclosure. Technically, the answer is yes you can convert a sealed subwoofer box into ported, it will work, but it might not sound like a proper ported box. Let me explain. A sealed box has less air space than a ported or vented designed subwoofer enclosure. Ported boxes are required to be larger to benefit from the ported design.
If you want to know how to make a sealed box louder, you can port a sub box using an PVC pipe, but you will need to know if the cubic feet of the prefab box you got are sufficient for being ported. It is no good to port a sealed prefab box if the box is not meeting the internal cubic feet of a ported subwoofer box. It will sound better sealed. Use an online subwoofer enclosure calculator to help you work out the internal cubic volume. Click here for my favorite one I always use when building boxes. Just enter the required measurements into the calculator and it will work it out for you. You can also use the subwoofer port calculator on the 12volt.com website to help you work out the tuning frequency of the port, factoring in the diameter and port length. If you are wondering what I mean by the word tuning frequency, the port is designed to be fitted to play up to 3 DB of bass in a dedicated frequency region. So, for example, if you tune your port to 30 HZ, it will play anything from 25 HZ to 33 HZ usually effortlessly and the higher frequencies not around tuning will drop off. The port allows you to fine tune your subwoofer to play what you want to hear at a louder decibel.
In most cases, you will find after using the subwoofer enclosure calculator on the 12 volt website, that your prefab sealed box is too small to be ported. Most say a sealed box can't be ported because it’s too small, this is true to some extent. There are ways to increase the internal cubic feet in a prefab sealed subwoofer box so that you can port it. You can invert mount the subwoofer to increase the air space inside. This is a fancy word for mounting the subwoofer backward so the magnet is sticking out. The magnet takes a huge amount of space up inside the box, doing so will free up space.
Also, you can add polyfill inside the sealed subwoofer box. This is white stuffing that you can extra from old pillows or you can purchase in bags at your local department store. Add a sensible amount inside each wall section of the enclosure from top to bottom will add a nice bit of extra cubic volume inside the box. This will allow the subwoofer to play deeper and sound more punchy.
Once you have made the sealed enclosure that you want to port using PVC pipe larger, it’s time to get constructive. Once you have used the subwoofer port calculator to work out what tuning you want, you may want to increase or decrease the port length. If you want to cut the PVC pipe simply use a handsaw and file down the edge using sandpaper. You might also want to flare the opening of the PVC port using a heat gun and a metal bowl. You simply place the PVC pipe onto the bottom of the metal bowl, keep twisting it while applying heat directly to it until the end becomes flared. Flared ports tend to prevent port noise at loud volumes.
The best port placement is usually at the front of the subwoofer box. Place the PVC aero port that you want to add to the sealed sub box, getting a marker pen, and draw around it. Using an appropriate-sized circle cutter to cut into the MDF. Sand down the edges for the perfect finish and drop the port in. You may want to use some silicon glue inside the box to seal around any air leaks around the cutting of the port. This will prevent any port noises of chuffing on low deep bass notes produced by your car subwoofer.
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