Note: This is not meant to be all encompassing, only a quick and dirty run down on the subject. There are more aspects involved than I can very easily cover in this, however feel free to ask any questions you may have.

It's a given, well known fact that not every audio enthusiast in the world can design or build a proper ported enclosure. There are many tough formulas involved, considerations about the sub being used, the environment it's going to play in, and the goals of the end result that are all tough to factor for. Because of that fact there are many people out there who will buy a prefabricated ported enclosure for their sub(s).

Now, buying one that was built or designed by the manufacturer of your subs will guarantee that they will perform as the manufacturer intended which is a good thing. Buying an enclosure that was mass produced can work as well, however there's no guarantee that it will yield the best performance, output or sound quality either. I believe that this is the reason most people associate ported enclosures with only getting loud and sealed enclosures with sounding good. They've never had the opportunity to listen to a well designed, well built, well executed ported enclosure however that's for another topic.

The problem with almost every ported enclosure you buy off a shelf is that you have NO idea what it is tuned to. Knowing the tuning frequency of the enclosure is important for many reasons. The two most important reasons are: 1. Knowing the kind/type of music that's going to sound the best or get the loudest (depending on your goals). 2. Knowing where to set your SSF (sub-sonic filter) so you don't destroy your great new subs. "Destroy?!?!?!?" you may ask with surprise, yes destroy.

A ported enclosure is tuned to a specific frequency which is determined by the size and length of the port in the box. The air which inside the port has mass, not much but it's there, and so does the air inside the enclosure. When you play frequencies above the tuned frequency of the enclosure the sub is moving or exciting the air inside the enclosure faster than the air in the port can be excited. The result is that the air inside the enclosure acts like a spring and controls the cone's movement almost exactly like a sealed enclosure does. As the sub plays frequencies closer and closer to the tuned frequency the air in the port becomes more and more easily excited. It does this so much so that when the sub plays the same frequency that the enclosure is tuned to the air the sub moves outside the enclosure and the air moving inside the port are actually coupled and combined. That's where the big increase in output over a sealed enclosure comes in, pretty cool eh?

The problem here is that below that tuned frequency the air moves too easily and offers no resistance to the cone of the sub. That lets the sub play as though it's not even in an enclosure and while doing so with only a few watts of power probably won't hurt anything at all, if it happens when you're driving full power into your sub you'll likely do serious damage. The kind of damage that results from this are bent or broken voice coils, torn or broken spiders, broken tinsel leads, glue joints and cones, torn surrounds and any combination of the above. No one wants to learn they've just grenaded their brand new subs, so on to the next part, how to learn what your tuning frequency is and how to set the SSF (sub-sonic filter) accordingly.

All you need to do this is a set of test tones ranging from about 20hz to 50hz in 1hz increments at the very least, and a decent eye. The test tones can be mp3's or on a cd, doesn't matter. Set your SSF as low as possible to start this test. Start playing the test tones from about the 50hz area and step down one hertz at a time. You'll want to play them at a decent enough volume level to get your sub(s) moving good enough to see the movement but not going crazy. As you step down you'll see them start to move a little more, then as you near the tuning frequency the subs will move less. They will be the loudest and move the least (they'll almost look as though they're not moving at all) at the tuning frequency, take note of the frequency you're on. At this point pick the track with the frequency that is 3-5hz lower than your tuned frequency and watch the cone's movemet carefully. It should really be moving, but make sure it's not moving too much. Dial the SSF up until the cone moves right about half the total movement it had. Your SSF is now perfectly set and since you know your tuning frequency you can pick music that fits your tuning the best for showing off.

The tuning frequency of your enclosure determines more than most can imagine and often times more than most experienced people know. There's enough about them to write an entire book about and there's quite a few out there. I'm just hoping that this will help some folks here understand their ported enclosures better, inform them about some of the concerns we should all have when utilizing this style of enclosure, and how they can help prevent damage to their subs and perhaps find just the right songs to really impress their friends.

 

Do most head units have sub sonic filters in them? or do you have to buy them separately?

 

The HU wouldn't have the subsonic filter in it, the amp does. Most subwoofer amplifiers do have them, although not all are adjustable most are. For some people who would use a powerful 2 or 4 channel amp to power a sub it's much harder to find one with an SSF built in.

 

Oh ok yeah now i remember hearing something about that being on the amp i have.