Acoustic Baffle / Absorbent Panel Construction Procedure
the main Eyedrum Acoustics Project page
for background info.
||Baffle cross section
||structure, improve LF absorption
||$12 for 4'x8' sheet
(burlap not shown in photo)
Owens Corning 703 compressed fiberglass insulation,
two inches thick, unfaced
||$7.36 x 2
|Polyester batting, 3 ounce weight -OR-
Polyester batting, bonded, 1/4-inch thick
|keep the fiberglass fibers from getting out
||$1.39/yard off 48-inch-wide roll -OR-
$8.99/queen-sized sheet (90" x 108")
|1.33 yards -OR-
|Fabric cover: white burlap
||$2.77/yard of 36-inch-wide roll
|Heavy duty hanging hardware
- The agreed-upon configuration is shown above.
See the simple cost calc spreadsheet.
- Cost per panel drops by $6.56 if 1-inch-thick OC-703 is used
-- but less thickness means less absorption.
- Cost per panel drops by $3.50 if natural (light brown)
burlap is used -- which is actually better due to a more "open"
weave, and the natural color may blend in better with the unpainted
wood joist ceiling. However, having met with the architecural
consultant, she thinks white panels will look better, and effectively
provide a visual "drop ceiling" in the space that we plan to use them
- Hardware cost is not known yet -- I'm not sure yet how I'm going to
hang these. It has to be absolutely safe (we don't want these things
falling from the ceiling), but we don't want to spend $20 per
panel on hardware either. See bottom of page for more information
about the hanging hardware.
- Also need to treat burlap with fire retardant. Cost not yet known.
Here's one product.
Could also get it done at a commercial cleaners.
- Instead of burlap, if you've got the money, you can use real
acoustic fabric such as
It costs $18 per linear yard (66" wide), so that's $30 per panel. Ouch.
That's too much for a DIY baffle project like this, but if you're
interested, order directly from Guilford at 1-800-544-0200.
- The OC-703 is 55% of the cost. Since I'd be buying $500 worth
of the stuff (72 panels), maybe I can get that discounted a bit.
- Since we're building these ourselves, there's nothing that says
we can't build these panels to custom sizes. Specifically, I'm
thinking 2'x6' (instead of 2'x4') because that will fit better
between the HVAC duct exhausts. But that will have little to no
effect on the total material cost.
Tool / Hardware List
In addition to the major items listed above, you'll need the following:
- drill with assortment of wood bits
- roofing nails with "washers" -- (1.75-inch long is OK, 2.00-inch is better)
- regular scissors, measuring tape, flathead screwdriver
- 7/16-inch wrench -- box or socket
- power stapler of some sort and staples (7/16-inch T-50 staples are ideal);
need about 150 staples per panel; manual staple guns suck.
- a hammer, preferably a small-sized one and a regular-sized one
- hooks for the baffles
(should screw to side of wood -- try 3.5-inch
- screws to attach the hooks to the plywood -- 1/4" x 1" hex head lag screws (7/16 hex head)
- hooks for the overhead joists (standard screw-in type)
- chain or aircraft cable assemblies (see bottom of page for discussion of that issue)
Baffle Construction Procedure
It takes about 2 man-hours per panel to do this procedure, assuming you
know what you're doing (i.e. this isn't your first one) and you've got
all the tools and materials ready. More than half of that time is taken
up in affixing the burlap. Due to setup time overhead, it is recommended
that you build these in batches, instead of one-at-a-time to completion.
- Cut the plywood down to 24.5" x 48" panels -- that's a half-inch MORE
than 24" x 48". This means you'll
have three per 4' x 8' sheet with scrap left over. The extra
half inch means you'll have
a 1/4-inch extra for the top and bottom edges, which will support
the baffle when resting on the ground -- if the fiberglass panels
have to support the weight of the panel, they are likely to
shear off of the plywood (they won't be very well attached).
Also, it makes the stapling part a lot easier.
The rest of this procedure sucks if you use 24" x 48" panels --
spend the extra buck per panel for the 24.5-inches.
- Drill four 11/64-inch holes in the plywood for the two hooks.
The hole pairs should be 8 inches from each side edge
(32 inches apart), and the holes should be placed 7/16-inch and
1+9/16-inch from the top edge (1+1/8-inch apart).
Which edge is "top" is arbitrary -- pick one.
- Get the hooks and remove any pricing labels from them
(it's easier to do it now than to do it later).
Attach the hooks using the lag screws. Orient the hook so that
it goes "up and over" the edge of the plywood and points down the "back" side.
Hand tighten -- don't strip the plywood. The tips of the screws
will probably poke through the back side
-- that's OK, the fiberglass panel will cover that.
- For the next few steps, be sure to keep your hands away from your face,
until you've wrapped the fiberglass panels in the polyester batting.
- Place the plywood flat on the ground with the hooks pointing up
in the air -- so the "back" side will be facing up.
Place one of the
fiberglass panels on top of it, centered on the plywood.
Nail the fiberglass panel to the plywood using four roofing
nails with "washers". 2.00-inch nails are ideal, but
1.75-inch nails will do if that's all you can find. If the
nails are "too short", help the washer push through some of the
fiberglass insulation as you nail it in
-- push the washer edges with your fingertip;
it just shears right through it.
Nail in a zigzag pattern as shown at right -- this ensures that
the nails on the opposite sides of the panel will not collide
with each other. Use a few heavy hammer blows, otherwise the nail
will bend and you have to try again with a new nail.
Pound each nail until it's just barely through the board.
You may have problems with this step if the plywood is warped.
After each nail, make sure the fiberglass panel has not shifted.
- Flip the assembly over and attach the other fiberglass panel.
- Cut a 60-inch length of polyester batting (should be 48 inches wide)
and lay it out flat on the floor. If you got the queen-sized sheet
kind instead of the rolled kind, cut the sheet into three 60"x45" pieces
(with one 30"x45" piece left over).
- Place batting on top of the assembly so that there is 5 inches
of batting extending past the top edge of the assembly
(the edge with the hooks) and a little bit extending past the two sides.
Tug the batting around until it is straight and lined up with the panel.
Smooth the batting against the top edge of the panel -- it should stick.
- Lift the panel by the side edges and rotate it in air so that the bottom
edge goes up and over, and place the panel back down. Smooth the batting
and overlap it with the other batting flap on the top edge of the panel.
Be careful when you move the panel -- PICK THE PANEL UP off the
floor, rotate it in air, and place it straight down either
A) flat on one of its two faces, or B) on its edge so
that the plywood touches the floor and supports the weight. If you
tilt the panel up off the floor, and/or lean it
against a wall, the weight will be supported by the fiberglass panel,
and the nails will probably pull out.
As you do this, pay attention to whether the fiberglass panels
stay nailed to the plywood. If not, then you'll need to bash the
nails in harder, or use longer nails.
- Trim the batting on the top and side edges. On the top edge, the two
batting flaps should be completely overlapped and each should reach
nearly all the way across to the far edge (~4 inches).
- Unroll and cut about 110 inches of the burlap.
Don't let the burlap ever get folded (e.g. at any time after cutting it at the
store) -- it creases easily and the creases don't come out, like linen.
Keep it rolled up, just like they had it in the store.
- Place the burlap on the assembly lengthwise so that there is 5 inches
of burlap extending past the side edge (pick a side). Center the
burlap vertically so that there is plenty of burlap (8 inches or
more) extending past the top and bottom edges. If necessary, skew
the burlap so that the grain of the fabric lines up with the edges of
- Stand the assembly up on the other side edge, bring the burlap up
with it. Be careful when you do this -- PICK THE PANEL UP off the
floor, rotate it in air, and place it straight down on its edge so
that the plywood touches the floor and supports the weight.
- On the edge that's now facing up into the air. trim the burlap so
the edge of the burlap is about 1 inch
back from the corner of the assembly edge, or about 1 inch beyond
the plywood edge.
- Staple the burlap to the plywood edge. Pull the burlap
up gently as you do this and keep the tension equal across the edge.
Try to run the grain/weave straight, too. Tap the staples in with
a hammer if necessary.
- Pick up the panel and rotate it in mid-air so that the remaining
burlap is pulled up over the other edge. Make sure the burlap
weave parallels the panel edges. Trim the burlap as above.
- FOLD THE BURLAP UNDER (about a half inch) and staple it to the plywood.
Do this stapling neatly because people will be able to see it. Tap
the staples in with a hammer.
- Now rotate the panel so that it is resting on the hooks (upside down).
- Trim the burlap
on the bottom edge so there's 1 inch beyond the plywood, as above.
Staple as above, folding the corners like you would wrap a gift.
This will be the most visible part of the panel, so work as neatly as
possible on this seam. Tap
the staples in with a hammer. You may want to use one of the big
"heavy duty metal staples" at the two ends (hammered in) because the
fabric folds get pretty thick there and can pull regular staples out.
- Pick the panel up and rest it on the bottom edge that you just stapled.
- Staple the burlap to the top edge as above.
You'll need to cut two slits for the the two hooks to poke through.
Treat the baffles with fire retardant
The fiberglass panels are basically OK as far as your local fire code
goes -- look for information about that on the side of the bale of the
fiberglass panels. Same goes for the polyester batting, and perhaps
even the burlap. But to be safe, you should apply some retardant. I have
which costs about $25 per 1-quart bottle, and covers about 10 panels.
Vacuum each panel first (to get rid of loose lint) and trim off any loose
strings. Then simply spray the liquid on using a spray bottle.
Hang the baffle
There are three proposed ways to hang each baffle. All three ways have
the same four hooks installed on the baffle edge (2 hooks) and on the
overhead joists (2 hooks). The baffle hooks are not installed
using standard threaded-shank screw hooks -- instead, special
"side-bolting" hooks are used. This is much more secure -- the threaded
hooks are likely to eventually pull out of the plywood edge.
The three ways to hang it:
Note that while an extra $3.00 for the aircraft cable solution sounds
reasonable, multiply that times 30 panels and you just spent an extra
$100. Plus the labor required gets very big when building 60 of them.
- Hang it right up against the joists, hook to hook.
- Cost: zero
- Pros: cost, no swinging
- Cons: up too high, no height control
- Hang it displaced down from the joists using chain.
- Cost: about $2.00
- Pros: height adjustment is easy; ready to use, no labor required
- Cons: some cost; possible swinging; visually distracting
- Hang it displaced down from the joists using aircraft cable.
- Cost: about $5.00
- Pros: visually subtle; clean lines
- Cons: height adjustment is impossible (need new cable/clamp);
cable links are labor intensive to build;
high cost; possible swinging
The main problem with the chain is that it draws the eye, and you usually
want these panels to NOT be noticed. There is black "decor" chain, but it
is flimsy and designed for cosmetic/decorative use only. I strongly recommend
you use "real" chain, because these will be hanging over peoples' heads.
One cheap option would be to simply paint the chains white (or black,
or whatever you want). In fact, that's what I ended up doing, and it
looks great. Simply dunk each 24-inch length of chain into a can
of black paint and hang it vertically to dry. Catch the drippings back into the
can for the first two minutes or so. The paint I used was
Ace Hardware Indoor/Outdoor Rust Stop -- Flat Black
(need about 0.4 ounces per chain) and it looked
great, certainly from a distance.
More hooks and chains can be used if you want it to be even more secure,
or to inhibit swinging. Swinging could also be inhibited by very small
string (e.g. fishing line) run from the bottom of the chain to a point
away from the panel and under slight tension.