Everyone hide in a corner it's a "SETUP"!
Most people think that subwoofer setup is the easiest of all the speakers to accomplish when actually it’s exactly the opposite. Most full range speakers whether they are L,C,R’s or surrounds, box speakers or in-walls you get what you get. Nothing on the speaker itself is variable with a few exceptions. A few manufacturers offer high frequency attenuation switches with something like +/- 2db and even a smaller number of manufacturers will provide you with various plugs to tune the factory ports on the cabinet allowing you to “tighten” up or “open up” the low frequency response of the speaker. Subwoofers on the other hand, in particular active subs, give you control of the individual volume, crossover frequency, possibly subsonic filter, phase switch or ½ space, ¼ space and 1/8 space switches. Before we discuss how to set up your sub to work with your system there are several things we need to know and questions we need to ask ourselves. Some of the most common questions are listed below.
1. What size sub are we working with (15” or 8”)?
2. What factor is most important when deciding on placement, performance or aesthetics?
3. What type of speakers are we integrating the sub with; large floor standing speakers or small bookshelf/in-wall speakers.
Let’s look at question no.1 for a moment. The size of the subwoofer is vital when determining room placement. The 15” sub is much more forgiving in placement because it will have a much lower fundamental frequency and is capable of much higher sound pressure levels. However the downside is it’s much larger and therefore not as easy to hide so it could be considered an eyesore. The 8” subwoofer will be limited to how low it can play and the sound pressure levels it can achieve. As the size of the room increases the performance of the 8” will diminish dramatically. Small subwoofers will always benefit from being placed in a corner where it has three reinforcing surfaces to couple with incorporating as many as the backwaves as possible with the forward movement of the driver as possible. This is known as 1/8 space.
Question no.2 has been known to end marriages! Just kidding but this is often an overlooked element during system design, where is this behemoth going to go! The 8” sub is obviously much easier to hide, in a cabinet, behind a chair or under an end table etc. The 15” sub however is like putting a tutu on an elephant. When you’re done it’s still an elephant. Many 15” subs end up in a corner tucked behind plants or a piece of furniture. As mentioned before this can enhance or reinforce the output of a subwoofer, but when are starting out with a 15” sub this can sometimes be a problem. It can often make the sub sound boomy and lose definition resulting in a sloppy sound. There are a couple of things that can help in this situation. If the sub has a subsonic filter, engage it. This will prevent frequencies below the range of human hearing from exciting energy within the room that will couple with the harmonics of the frequencies you can hear and cause problems. Secondly you can use a bass trap such as a LENRD from Auralex Acoustics that is engineered to prevent the build up of low frequency energy in corners.
If you don’t have access to a LENRD or other device specifically designed for low frequency you can take several layers of the standard 12” x 12” wall squares and layer them for about the same effect. If you use the thin ones I would layer about six of then, if you have the 2” treatment three layers should do pretty good. Lastly always make sure your sub is on spike no matter the size!
Finally let’s look at what kind of speakers we are using with our subwoofer. If you have floor standing speakers with respectable low frequency response and you are adding the sub simply for sub frequency reinforcement and adding impact for movie soundtracks you can set the crossover frequency fairly low. Frequencies below 60hz are felt more so than heard. Sometimes rolling off the crossover at 60hz is enough to add that realism you are looking for when watching movies. Crossover settings of 75-90hz are more common with moderate speakers. If you use your setup for a lot of music playback or music videos I would suggest raising the roll off frequency to 100-125hz which will allow the thump from the kick drum to play adequately through your sub. The reason for the suggested ranges is that each sub manufacturer will use a different ‘slope’ or rate at which the frequency drops off beginning with the center frequency you have selected. Some are very steep (24db per octave) meaning wherever you set the center frequency the frequencies above it will be suppressed very rapidly. On the other hand those with a gentle slop (6db per octave) the frequencies above your center frequency will be suppressed very gradually. See article on crossovers for more information.
by Jason Levert