How To Add A Subwoofer To Your Monitor Setup

So you want to add a subwoofer to your monitor setup? Studio subwoofers can be tricky things that require a little bit of audio soul searching, auditioning, and planning to pull off well. But, a well integrated sub can make a world of difference in the right circumstances.

I, for example, just added a Mackie HRS-120 sub to my HR824 speakers and am quite happy with it after some tweaking.

Since pro audio subs tend to be expensive and add complexity, there are a lot of important questions that one should ask one’s self before investing in a quality sub.

Why do I want to add a subwoofer?
What kind of music do I tend to work on?
Do I even like the sound of subwoofers? Is my room suited for subwoofers?
What are the options that make sense for my existing speakers?

Why do I want to add a subwoofer?

The most obvious answer to this question is that subs theoretically allow greater low-end extension. But, there are a lot of other reasons for adding subs. Since bass takes the most energy to produce, it’s also the most costly in your headroom. Adding a sub can relieve your main speakers from the task of low-end reproduction which, with cheaper amps or low wattage speakers, can actually help them produce cleaner sound. Extra headroom is always a good thing even if you don’t take advantage of it. If you find that you tend to push your mains on a regular basis to the point where they’re clipping or farting, there’s a good chance that adding a dedicated sub unit will help quite a bit.

Another really good reason to add a sub is to do surround mixes. There’s just no way to do film work without one.

A high-end pair of mains and quality amps can achieve close to the same frequency coverage but with better phase and imaging than subs provide. Many audiophiles swear by subwoofer-less speakers. What is more important to you? Frequency response & volume or stereo image and phase?
What kind of music do I tend to work on?

Some monitors, such as the infamous Yamaha NS10s, have very conservative bass reproduction. This is generally fine for many types of music that don’t have a lot of extreme bass or transients such as classical music or rock and roll. Trying to mix dub, hip hop, electronica, or even jazz can be challenging on such speakers (and, indeed, sometimes that’s what people like about them). Many of contemporary genres require the addition of bass and careful use of compression to achieve the sounds people expect.

A good rule of thumb is to monitor on speakers similar (at least in general configuration) to what your audience will be using. If your audience is going to be cruising in cars with trunks full of woofers, it would be a little silly to skip a sub altogether (although I wouldn’t recommend lining your studio with 12″ Cerwin Vega bass cabs, obviously).

Adding a sub will enable you hear more of the bass frequencies as distinct notes rather than as indistinct tones. This can help substantially in tuning instruments and getting the dynamic layered response of bass instruments in the pocket. But, again, some genres won’t benefit as much from the addition. While sludgy Black Sabbath style rock can be mixed with lots of bass guitar and kick drum, for example, speed metal generally requires a lighter mix to avoid a blurry mess. In this situation a sub may make the task more confusing than it has to be.
Do I even like the sound of subwoofers?

For years I didn’t like the sound of subwoofers. Why? I always felt like there was too often a hole where the frequency response of the mains and the sub overlapped (called the cross-over frequency). In poorly integrated systems the crossover frequency can be inaccurate, creating either a gap or a bump in response that can throw everything off.

Another reason I didn’t like the sound of subs was I felt like the bass frequencies were coming from nowhere in particular, whereas with standalone monitors the bass is clearly localized and more or less originates from the same place the rest of the sound comes from. This just seemed more natural to me. Even most professional sub installations don’t satisfy me in this regard – the bass just seems to be coming from nowhere.

One thing I’ve come to realize is that I don’t dislike subwoofers per say, I just like the crossover to be tuned very low. You see, our ears localize midrange sounds best and, as you go up or down the frequency spectrum, we have a harder time figuring out where the sound is coming from. This means that very low bass frequencies don’t even register as having much directionality. The higher the bass tuning, the more our ears will notice the bass is not coming from the same place as the rest of the sound. So, I tend to be very sensitive to the crossover point.

Many mastering engineers even use stereo subs to get around this quirk, allowing the stereo image to continue all the way down.

If you’re like me, you may be better off just investing in mains that have substantial bass extension of their own. There are many choices out there that do just that. If you can afford and have the space for wall-socketed farfield mains, there are really good options out there with excellent bass response. Often good farfields have responses that rival dedicated subs but with better imaging.
Is my room suited for subwoofers?

If your room is not properly tuned or is too small, adding a pro audio subwoofer will likely be a disaster. Small, boxy rooms with low ceilings can produce some insane resonances with the lower frequencies subs produce. You’ll end up with a big mess. Subs work well in rooms that have either been acoustically isolated from the surrounding building or are large enough to accomodate the size of low bass frequencies. My sub goes down flat to 19hz – which is a wavelength of 59.2278 feet!
What are the options that make sense for my existing speakers?

Some speakers lines have matched subwoofers which integrate well. The NS10s had their YST-SW100 and the Mackie HR824 and 624 mains have the HRS-120. Matching speakers with subs designed for them will usually produce the best results. Mixing and matching speaker series will take a lot more tweaking and knowledge. Crossover points may not line up, tonality may not be consistent, etc.
Things to consider

Since my HR824 monitors have response down to 37hz, I was able to satisfy my preference for a low cross-over by setting the sub to pick up at 55hz and below. The majority of bass directionality still comes from my mains, while the sub extends the low-end nicely.

Phase coherance with a sub is very important. High-end cross-overs may have the ability to tweak the phase from 0 to 180 degrees, allowing you to find the point of greatest coherance. My HRS-120 simply has a phase invert switch, which fortunately has been good enough as the speakers are matched properly. When using third-party subs with off-brand mains, consider finding something that has a continuously variable phase adjustment.

Keep in mind that less is more with subs. If what you’re hearing says ‘oooh… a sub!’, something’s not right. Ideally a sub addition should simply sound like your original sub-less setup but with better low-end extension.

Placement is generally a trial-and-error proposition and is different for each room. A good starting point, however, is placing the sub in front of the listening position between the left and right speakers.

Dan Connor, Stereobus.com