Recording - February 2015 - 47

fiberglass board (the gold standard of
acoustic treatment) and 6" R-19 insulation
from the hardware store. Acoustical
absorption also comes from slabs of plastic
foam, but this isn't just any foam; it's
designed specifically for acoustic treatment,
and the degree of sound absorption at different frequencies is specified by the maker.
That phrase "at different frequencies" is
key, both for fiberglass and foam. The
unhappy fact is that thinner slabs are less
absorptive at low frequencies; in that
respect they're like blankets. That means if
you're using the kind of loose fiberglass
that comes in rolls, you want R-19 (6"), not
R-11 (4"). (If you use this or any other form
of fiberglass, by the way, you should wear
a mask and long rubber gloves. That stuff
is nasty in your lungs, or on your skin.)
There are plans for homemade absorbers
in Everest's books and on the RealTraps website; you should also check out my "Gadget"
design, which is now posted on the Recording
website (http://is.gd/DIYAcousticsGadget),
or Matt Seiler's "Make Your Own
Diffusers/Absorbers", again on the Recording
website (http://is.gd/DIYDiffusers).
Or you can make a rock-bottom
absorber, which I call a "Gadgette": Lay
a 36" x 74" sheet of cloth on the floor
(the cloth used for the underside of upholstered couches works well), put a 24" x
60" piece of R-19 insulation on it (using

mask and gloves!), then top off the sandwich with a 24" x 60" piece of 1/8"
waferboard. Fold up the edges of the
cloth and staple them to the waferboard
with a staple gun, then staple a length of
picture wire to the back and hang the
whole shebang on the wall. It ain't beautiful... but it works.
Soaking up the bottom
I said earlier that it's harder to soak up
low frequencies than mids and highs. So
what works down in those regions? This
is a long discussion, one you can find in
Everest's books and on the realtraps.com
website. Briefly:
~ Wallboard. Bass signals pass through
wallboard and out of the room rather
well, as you know if you've lived in the
wrong sort of apartment house.
~ Thicker absorbers. I talked about those
already; to soak up lower frequencies 6"
thicknesses are minimum, and 8" will be
better.
~ Bass traps, which can be wideband,
for general room treatment, or narrowband, to alleviate standing wave problems. There are some nice DIY plans on
the realtraps.com site, and Bruce Black
describes a DIY Helmholtz resonator in
March 2014. I've had good luck building
"Mankovsky boxes" using large plastic
tubs (sold for mixing mortar or concrete),

with a layer of fiberglass inside and
topped with perforated pegboard; see
Everest's books for details about designing these to soak up particular frequency
ranges.
Winding up
You'll notice that my descriptions of
room treatments have been pretty general.
That's deliberate, since I don't know what
your room looks (or sounds) like. You'll
need to decide what treatments to use,
and how many; for making those decisions, I once again recommend Everest's
books and the RealTraps.com website.
The folks who make Auralex also offer a
remarkable deal, through the dealer
Sweetwater: they'll plan out a treatment
for your room for free (http://www.sweet
water.com/shop/studio/acoustic-treat
ment/room_analysis.php). Of course,
they'll specify Auralex products, but that's
only fair.
I'll be back next month with some talk
about monitor speakers, plus a quick-anddirty room setup that'll get you started on
the path toward a neutral monitoring
space. Stay tuned!
Paul J. Stamler (stamler@recordingmag.com)
is a recording musician, engineer, radio
show host, educator, and collector of vintage
recordings, living in St. Louis.

http://www.realtraps.com http://www.RealTraps.com http://www.sweetwater.com/shop/studio/acoustic-treatment/room_analysis.php http://www.sweetwater.com/shop/studio/acoustic-treatment/room_analysis.php http://www.is.gd/DIYAcousticsGadget http://www.is.gd/DIYDiffusers http://www.realtraps.com http://www.adkmic.com http://www.adkmic.com

Recording - February 2015

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