Bass in Place: Setting Up Your Subwoofer
There are times when a person just needs more bass.
Sometimes it's to hear the heavenly metal of AC/DC's "Highway to Hell" and
sometimes it's to get all the way to the bottom of Charles Mingus's syncopated
explorations or to ride the Kodo drummers' oceans of sound. If you find yourself needing
more bass, for whatever reason, you might find yourself looking at subwoofers at your
local audio dealer.
Woofers are the cones and drivers in your loudspeakers that
reproduce bass; subwoofers are, as the name implies, a special subspecies of woofers.
Subwoofers are like sonic miners tunneling into rich, dark veins of sound below where your
speakers can go. They reproduce buried bass more accurately and fully than most full-range
speakers.
When you're out shopping for a sub, you're going to see
some relatively inexpensive products labeled as subwoofers that are really just
outboard woofers. The "subwoofer" you see at the megabox audio store
priced at $119 is actually just a woofer -- very possibly not even as good as the woofers
you already have in your speakers -- which might or might not extend your bass. These
products get nowhere near putting out low-distortion sound at 20Hz and below, a sonic
benchmark for a product to be considered a true subwoofer. The problem with "true
subwoofers" is a familiar one: They cost a lot. Typically more than $1000. "I
can't afford that," you might be thinking. No problem. If you're like most people,
you're going to discover that a sub that gets down to 25Hz or 30Hz will give you all the
bass you need; most music is above 30Hz. Plus, the prices of these effective subs are
considerably lower than the "true" ones. (Check out the review of the $499 Hsu Research VTF-2
in the GoodSound! archives for an example of one such sub.)
Let's assume, however, that you've made the decision to add
a subwoofer to your system and have it sitting in its box at home, ready to go. All you
need to do is unpack it, hook it up and . . . and . . . where are you going to put it?
That's what we're going to figure out right now.
If you recall from our earlier piece on loudspeaker placement, your
speakers and you should form a triangle. This will most likely be an isosceles triangle
(one with two equal sides -- the distances between you and the two speakers -- and one
shorter side -- the distance between the two speakers). One might logically conclude that
the subwoofer should go directly between the two speakers so as to disperse its bass
across the soundstage perfectly evenly. Perhaps, in your room, that will turn out to be
the final resting place of the sub, but, hopefully, not until you've explored some other
positions first.
On your knees!
The simplest way to place your subwoofer is to put it in
your listening position and then go around the room trying to find where it sounds best.
Think about it. If the sub is sitting in your favorite spot for listening to music and
you're by your bookshelves and the sub sounds good, the sound should be the same when you
reverse positions, putting the sub in the corner and you in your favorite comfy spot.
When employing this method, play some simple music that
you're familiar with, so that you'll be able to focus on changes in the bass as you move
around the room. On your knees. Yeah, you'll be on your knees so that your head can be
close to the floor, which is where your sub will be sitting after it's been properly
placed. If you can figure out a way to elevate your subwoofer in your listening position,
so that it approximates where your head will be when listening to tunes, so much the
better.
When you're on your knees, you might well find spots where
the bass is so muffled as to be almost nonexistent. What you've probably found is a bass
null, a sort of black hole where sound waves cancel each other out. No one wants nulls or
peaks in their listening room, but they're a part of our real-world listening lives.
(Peaks are sound waves that reinforce each other rather than cancel.)
There's nothing particularly worrisome about a null, as
long as your listening position isn't in one. Because, if it is, maybe that's why you've
purchased a subwoofer. And maybe if you move your listening position, you might well hear
more bass and find that you needn't have purchased the sub in the first place. So, before
buying a sub, try moving your listening position forwards and backwards, noticing subtle
changes in the quality of the bass. You might well find a spot where the bass is more to
your liking, erasing the need for a sub.
(Note: Many subwoofers aren't magnetically shielded, which
means they should be kept away from your television set so that they don't interfere with
its picture.)
Go to your corner
One of the most common places people put their subs is in
the corner of their listening room. It makes lots of sense when you consider that
subwoofers are usually big black boxes; not what most of us want front-and-center in our
living rooms. A sub can sound good in a corner, too. (Even if your room or tastes simply
dictate that a sub be in a corner, you can still use the "on your knees!"
placement technique to determine which corner will work best.) The hard, reflective
surfaces of your walls will reinforce the bass in your music.
Make sure not to place the sub equidistant from the two
walls in your corner, however. In other words, don't put it a foot from the side wall and
a foot from the front wall. You'll get better sound when you have the sub staggered
between the two walls; one foot from the side wall and two feet from the front wall, for
example.
Also, be careful not to place the sub too close to the
corner. If you do, it'll start to sound boomy, meaning you'll be getting too much bass and
losing details in your music.
Phasing facts
Once you've placed your subwoofer, there are some things
you can do with it to further heighten the bass in your music. A lot of subs come with a
couple of basic controls: phase and crossover.
The phase control will help the sound waves from your sub
get synced up with those coming from your main speakers. If they arrive out of phase,
there's the tiniest delay between Mick Jagger's voice and Bill Wyman's bass, for instance.
An easy, accurate way of setting the phase control is to
reverse the connections on your main speakers (the black wire goes to the red terminal and
the red wire to the black terminal). Now play a simple selection, like a jazz instrumental
with a good walking bass line, on your system while you're sitting in your listening
position. Have a friend dial the phase control on the sub until you hear the least
amount of bass. Leave the setting there. Returning your speaker wires to their proper
places will now allow you to hear the most bass from your sub.
(If your sub doesn't have a phase control, you're going to
want to position it as close as possible to one of your main speakers in order to ensure
that the sound waves are synced up.)
Crossing over
The crossover switch allows you to direct where the low-
and high-frequency sounds will go, either to your main speakers or your sub. Obviously,
you'll want the low-frequency stuff coming out of your subwoofer.
Subs typically have more than one crossover-frequency
selection available (some even give you a range of, say, 40Hz to 120Hz to choose from).
You'll want to try them all to see which one integrates your sub best into your system.
Your owner's manual should be able to give you specific instructions on how to set the
crossover properly on your particular subwoofer.
Setting the crossover too low will mean that you'll have a
gap between the frequencies the sub reproduces and those coming out of the speakers. In
other words, some sounds won't be getting reproduced by either your mains or your sub.
Setting the crossover too high means you'll have sounds
coming out of your sub -- high-frequency sounds it wasn't designed to handle as well as
your mains -- that will be thickened and muddied.
A good rule of thumb for setting the crossover: if your
mains are big, with good bass response, your crossover setting is probably going to wind
up between 60Hz and 80Hz. If you've got bookshelf speakers, the crossover point will
likely be higher (80Hz to 100Hz).
Final exam
When you've finished placing your sub and setting its
controls, you should be able to bring a blindfolded friend into your listening room, play
a song for them, and ask them to point to where your sub is sitting. If all has gone well
during setup, your friend will be unable to locate the sub because it's been integrated so
seamlessly into your system.
A sign that you should make further
adjustments to the placement of the sub or the setting of its controls is when the sub
calls attention to itself. The music is, after all, the focal point of your system, not
the equipment.
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