| Part of the reason that professional studios get such a good
recorded sound is through the use of sound-absorbing baffles. Here are plans
for inexpensive baffles you can make for home recording and suggestions on what to do if
you can't even afford the "cheapie" baffles. |
| HOW
TO USE BAFFLES |
| Before we get into building baffles, let's do a quick review
of how baffles are used in recording. |
| In professional recording, loud
and soft instruments are often placed in "isolation rooms." These rooms are
adjacent to the recording studio and are connected by windows and doors to the studio. At
home, any other room may be used but it should have a minimum amount of hard surfaces.
Often musicians have difficulty playing together if they do not have a good line-of sight
with other musicians. If we run out of rooms, or the use of rooms results in poor line-of
sight with other musicians, we place the instruments in the same room and achieve
isolation by distance and by use of sound-absorbing baffles. |
| Because of the reflective nature of sound we can usually
achieve the best sound isolation by placing the absorbent baffle behind the very loud or
very soft instrument. Directional mics are placed so that they point into the baffle; this
rejects any sound coming into the area because the back of the mic doesn't pick up sound
well. The sound absorbing baffles prevent reflections of sounds from bouncing into the
front of the mic. The musician is placed between the mic and the baffle, with the
musician's sound projecting into the front of the mic. Figure below shows this set-up. |
|
PLACEMENT OF BAFFLES AND MICS FOR
ISOLATION |
|
CONSTRUCTING
BAFFLES |
| The two drawings below show the construction of an
inexpensive baffle that I designed for a studio. |
|
|
SOUND ABSORBING PANEL |
BIRD'S EYE VIEW OF COMPLETED BAFFLE |
|
| The sound-absorbing panel is made by putting together a frame
of 2x4 studs. The drawing shows it 96 inches (8 feet) tall, but this can be modified
for your ceiling height. Over the frame, a 8' x 4' solid Masonite panel is tacked to
the frame. This Masonite should not have holes (don't use pegboard). Strips of
building insulation are put between the 2x4 frames. (Use the type that does not have
any cover paper and wear rubber gloves when handling the fiberglass insulation.) The
exposed fiberglass side of the panel may be covered with a cloth or with plastic screen
material to both hold the fiberglass in place and to prevent musician contact with that
itchy fiberglass. |
| The base is made out of 3/4 x 8 pine and has a special shape
as shown. The sound absorbing panels are bolted to the base with two (or 4) quarter
inch bolts. Small castors are installed on the bottom of the bases. Finally
the two mounted sound-absorbing panels are hinged so that the baffles can open and can
close per the bird's eye view. We used a 4 foot continuous (piano) hinge to connect
the baffles. The two baffles can "open" to about an angle of 120 degrees
because of the shape of the base. (This provides stability to the baffles when they
are open). The baffles can close-up and take up minimum space when they are
not in use. |
| Helpful Hint: I learned this
the hard way. When picking out the wood, make sure the lumber is straight and not
warped (I knew to do this). Construct the baffles right away and "seal"
the wood with a good paint or shellac - this can prevent the moisture from getting into
the wood and warping it. (Guess how I found this out.) Remember that basements tend
to be damp. |
| WHAT
TO DO IF YOU CAN'T AFFORD (OR DON'T HAVE ROOM FOR) BAFFLES |
| The home recordist is usually
working with a limited amount of space. Often the live musician performing is in the
same room as the console and the musician is playing in the corner or across the room.
There's not a lot of room for big baffles, like there is in a larger professional
recording studio. |
| Big baffles can be expensive,
even when built with minimal costs, and for what? To take up most of the limited
space that a home recordist has - naturally. |
| So I decided to design a home
baffling system that the home recordist can actually use. The system I designed will
fit into any setup and cost a mere $3.00 (or $5.00 if you don't watch costs).
Probably everything you need can be picked up at your local dollar store. |
One takes a corner of the room
and hangs blankets 6 to 8 inches away from the wall. This "L" shaped area
has reduced leakage of other sounds in the room because the sound waves have to travel
through the blanket to the wall and back through the blanket to form a sound reflection.
The air space between the blanket and the wall helps make the blanket effective.
| So you get those hooks and clothesline that
will hold the blankets. You use things like clothespins to keep up the blankets. |
|
|
| Needless to say everyone has blankets and
you can't use your sleeping blanket while you're recording. You would want to
use the thickest ones or even have two layers of blankets {two thin blankets work better
than one thick one, by the way]. |
| So your little corner becomes your
baffled-off area and things sound better there and have less leakage |
| THE SOUND
ABSORBING QUALITY OF AIR |
| Air actually is a sound absorber. It
doesn't have as much sound absorbing ability as fiberglass or even the wool-blanket, but
it has sound-absorbing qualities none the less. The blanket baffle works because the
sound has to go though the blanket and then a layer of air before it reaches the wall.
After bouncing off the wall it goes though air again and then the blanket again. |
| The thickness of the baffle determines the
lowest-frequency that will be affected by the baffle. Lower frequencies have longer wavelengths, therefore they
need thicker baffles to absorb the sound. Putting the blanket 6 inches away from the
wall makes the baffle effectively 12 inches thick. Generally sound-absorbing
material can have maximum absorption for frequencies with wavelengths four times the
thickness of the baffle (or less). There will be noticeable sound absorption for
frequencies with wavelengths eight times the baffle thickness. |
LOWEST
ABSORBING FREQUENCY FOR A THICKNESS OF SOUND-ABSORBING MATERIAL |
FREQUENCY/WAVELENGTH |
PARTIAL
ABSORPTION |
MAX
ABSORPTION |
1000 Hz / 1 ' 1.5" |
1 3/16 Inches |
3 3/8 Inches |
500 Hz / 2' 3" |
3 3/8 Inches |
6 3/4 Inches |
250 Hz / 4' 6" |
6 3/4 Inches |
13 1/2 Inches |
125 Hz / 5' |
13 1/2 Inches |
27 Inches |
63 Hz / 10' |
27 Inches |
54 Inches |
|
| From the chart, it can be seen that the blanket baffle can reduce leakage
for frequencies down to about 125 Hz. |
| THE SOUND
ABSORBING WALL |
| Some studio will make one wall entirely sound-absorbing to help with the
acoustics. In a future Alexander Magazine issue we plan an article on the
when and why this is a good practice. Studios often buy sound-absorbing foam that is
about 3 inches thick and place it on the wall. Although there is an angled pattern
to the foam that helps absorption, it can be seen from the above chart that the foam will
have limited bass absorption. It can also be seen that placing half-inch thick
carpeting on the walls really doesn't work to absorb even midrange sound. |
| A much more effective way of making a sound-absorbing wall would be to
mount the acoustic foam on pegboard, and the mount the pegboard 3 to 6 inches away from
the wall. This use of the foam will reduce sound reflections well into the bass
frequency range. |
|
