Listening to Your Room: Solving Acoustical Problems
All listening rooms have acoustical
problems. The giant listening room known as Carnegie Hall has problems. While those
problems might not be as severe as the ones in an average listening room, they do exist.
Acoustical engineers have yet to figure out the perfect room in which to listen to music.
Some common problems in listening rooms include reflections
of sound from one wall to another, ceiling-to-floor reflections, reflections coming from
your sidewalls to your listening position, and out-of-control bass. Fortunately, you can
minimize all of these problems by taking some simple, inexpensive steps.
The first, and probably most satisfying, method of
correcting problems with the sound of your room is to get very wealthy, very quickly, and
hire an acoustical engineer to build you a Taj Mahal of a dedicated listening room. Since
that solution probably isn't going to work for everyone, try repositioning your
loudspeakers and/or listening position. See "The Best Things in Life are
Free: Speaker Placement" for more information on how to do this properly.
Not all problems can be fixed by rearranging speakers or
your favorite listening position, however. Let's take a look at how some immovable
objects, such as walls, and some irresistible forces, such as the laws of physics, can be
manipulated in your favor.
Wall-to-wall echo, echo, echo
When you have two parallel, hard surfaces (like walls)
facing each other, the soundwaves of your music can bounce back and forth between them
like a tennis ball between Venus and Serena Williams. This bouncing creates an echo effect
referred to as flutter echo. What you hear are echoes of your midrange and
treble, especially, going back and forth and blurring the music -- fluttering with a
metallic pinging.
A good way to check to see if your room might suffer from
echo is to stand in its center and clap your hands together sharply. If you hear a ringing
sound after the initial sound of the clap has disappeared, you and your room are being
tormented by the heartbreak of flutter echo.
Luckily, this is the sort of heartbreak that's easily
repaired. Take a look at those reflective walls of yours. If they're mostly bare, think
about adding a tapestry or rug to one of the walls, or if you normally keep your windows
uncovered, try pulling the drapes or curtains closed. Fabric can be a good absorber of
unwanted sounds.
Which way is up?
If you're like most people, and most people are, your
speakers will, by necessity, be on or near the floor of your listening room. If the floor
is uncovered hardwood, for instance, you might also have problems with echo -- this time
from sound bouncing back and forth between the ceiling and floor. Again, this can be
easily remedied by having the floor carpeted. If this is too expensive or aesthetically
unpleasing, try a throw rug or two, preferably made of natural fibers like wool.
Wool makes a better absorber of sound than the synthetic
materials used in lots of inexpensive rugs and carpeting, because the fibers in a wool rug
vary in length, thickness, and density. This variety helps diffuse the sound, and enables
the material to absorb different frequencies of sound, whereas the uniform length and
thickness of synthetic fibers enable them to absorb only one narrow frequency.
Think about this as well: If your loudspeakers are on the
floor, they're going to reflect more sound, especially bass, than elevated speakers.
Consider speaker stands if you've got problems with floor and ceiling reflections.
Another brick in the sidewall
A lot of people not only have to place their speakers on
the floor, but near sidewalls (the walls to the sides of your speakers) as well. It can
simply be the best, or sometimes the only, place to put your speakers. This placement can
cause problems in the tone of the sounds you hear, unfortunately. Unwanted tonal
coloration occurs in a couple of ways.
One common coloration occurs when the sound emanating from
your speakers hits the sidewalls. It then is reflected to your ears a fraction of a second
after the direct sound arrives. That means you hear the direct sound, and then a second,
weaker version of it, reflected from your walls. If your walls absorb a bit of the
high-end frequencies, that second (indirect) wave of sound will be colored differently
from the first (direct) wave. What all of that means is that the high end, midrange, and
low end of your music will be processed twice by your brain and colored by the delays in
time and the absorption. Result? Music that sounds less defined than you might hope for
from your music system.
Another way that your music can be colored by your
sidewalls is by off-axis reflections from your speakers. Off-axis sound comes from
the sides of your speakers. On-axis sound comes directly from the front of the speakers.
Speakers are generally designed to fire music forward, out of the cabinets, but since no
speaker design is perfect, sound always emanates to the sides as well.
These off-axis sounds often differ in tone from the on-axis
sounds. They might have dips or peaks in frequencies that the on-axis sound doesn't have.
When the off-axis sound reflects off of the sidewalls and then arrives at your ears just
after the on-axis sound, you've got unwanted coloration of your music.
A simple way of alleviating problems like these can be to
move your loudspeakers farther away from your walls. If that isn't possible, there are
simple, affordable solutions. First, try the suggestion from above: Hang a tapestry or rug
on the sidewalls between your speakers and your listening position. If that doesn't
diffuse the problem to your satisfaction, you might want to consider adding some highly
absorbent acoustical treatment to your walls. One of the most popular is Sonex. Even if
you've never heard the name before, you're probably familiar with the look of this
sound-absorbing stuff. Often used in recording studios to devour unwelcome echoes, it's
made of gray, open-cell polyfoam. Tiles of Sonex look something like futuristic
checkerboards with horizontal and vertical lines created by the sound-absorptive foam.
Four 2' x 2' tiles will cost about $75, and can make a world of difference in dampening
sidewall reflections.
Try putting four tiles, two on each sidewall, in various
places on the walls, always between your listening position and the speakers. Listen to
the same piece of music as you test the various locations. Very often, you'll find that
just these four tiles will solve the problem. If they don't, however, you can either buy
more tiles or you can build an inexpensive sound-absorbing panel of your own.
A typical absorber panel would be 4' x 8', built of 2"
x 4" boards, fiberglass, polyester batting, and a cloth covering. Nail the 2" x
4"s (or 2" x 8"s to make a thicker, more absorptive panel) into a
rectangle, with the short ends toward the ceiling and floor. Caulk the inside seams of the
rectangle so that they're airtight. Staple a covering of tightly woven cloth over the back
of the panel, then cover the cloth, on the inside, with polyester batting (available at
fabric stores). Cut and fit a length of fiberglass material inside the panel. (Fiberglass
and like materials come in varying thickness. If you're using 2" x 4"s, get
4"-thick fiberglass. The thicker the fiberglass, and your panel, the more sound it
will absorb.) Cover the fiberglass with more of the polyester batting. (The batting helps
ensure that the fibers in the fiberglass don't get outside the panel.) Now affix a
decorative cloth covering over the front of the panel. You now have a sound-absorbing
panel that can hang on your wall between the speakers and listening position, which will
swallow those unwanted sounds as easily as Marlon Brando chowing on cheesecake. The total
cost of two such panels should be under $70.
These sorts of panels can be placed anywhere in the room.
If you have reflections coming from behind your speakers, as is sometimes the case with
bipolar speakers (loudspeakers that deliver sound equally from the front and back), you
can place panel absorbers behind each speaker.
If you find that you've got sound reflecting from your back
wall (the wall behind you when you're in your listening position), try putting a sound
panel back there.
Shutting the TV up
Objects that sit near speakers, such as television sets,
can also be the source of those unwelcome reflections. Cover the TV with a cloth when
listening to music. The same goes for amplifiers, if you have 'em near the sides or fronts
of your speakers.
Sonic booms
If the bass from your system has a dense, boomy quality to
it, again, try repositioning your speakers (and subwoofer, if you have one). If you've got
everything placed as well as can be expected, you might need to take another step by
adding a bass-absorbing panel, much like the one we described above. The difference is
that a sheet of plywood or Masonite is nailed over the front of the panel. Drill .5"
holes, spaced 1" apart, throughout the panel. Just like that, you've got a panel that
will eat up a lot of that excess bass. If your bass is still too boomy, even after
installing one or more of these panels, make those holes bigger to allow more bass into
the absorptive fiberglass.
Remember: Before building or buying sound-absorbing
panels, please check the positioning of your speakers and listening position. This is
still the best, easiest, and cheapest (free!) way to get the best sound out of your
system.
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