A bit of a read but lots of good info.
If its good for an airplane made of AL it has to work in a rover......Right?
SOUND PROOFING LIGHT AIRCRAFT (and other
I first put these ideas down in 1990, in the form of an instruction sheet we handed out
with the Super Sound Proofing mat. Over the years we've added more to them, mostly
by feedback from users of the product and printed thousands of these little booklets.
You are invited to pass back your experiences with this and the other products that
have been added to our arsenal in the fight against noise. We've now got acoustical
foam materials to be used in Boats, Trucks and Cars as well as new materials used in
Architectural applications for home movie rooms, sound studios, gyms, industrial as
well as for band practice in the garage!
Our first specialty is aircraft applications as it is the most challenging! We are always
available for free consulting at anytime for any application, to help you with what we
know about methods and materials for soundproofing.
We provide free copies to groups and associations, just let us know how many you
The latest version of this manual is available from our website at
© Copyright 1992/1998 by Bill Nash - all rights reserved. Reprint rights granted
when full credit is given.
Much has been discussed as well as written about the noisiness of aircraft - inside
and out. Because of these valid concerns, sound measurements have been made that
indicate that sometimes the noise levels are so high in some aircraft that damage to
the hearing over the long term can and indeed does, result. Elaborate techniques
now exist to drastically reduce such noise. While time and expense are important
considerations, installing soundproofing is not a luxury; it is an investment in the
physical well-being of the flyers in addition to a valuable upgrade of the aircraft.
Information presented here is applicable to all types of planes from "puddle jumpers"
to jets. The addendum to this booklet has info regarding other vehicles as
well as business, shop and office.
In a properly soundproofed airplane, the radio can be used with speaker and hand
mike, instead of only the headsets. You will even enjoy better direct communications
between passengers and will not have to worry about damage to your hearing.
Contrary to popular belief, wearing headsets will not protect your hearing much.
After being properly soundproofed, using the latest space age materials, the noise
level in most aircraft will be so low you'll probably be able to have conversations in
normal tones. You'll wonder why you ever put up with all the noise before. The
quieter aircraft will seem to have gained quality and feel more solid and plusher.
Such an improvement should not be considered costly.
Before we tell you how to accomplish this, we will discuss some commonly used
materials for sound attenuation. Also, keep in mind that soundproofing involves two
(2) concepts that require two different materials:
1. Sound absorption, and
2. Sound blocking, or barrier material.
Vibration of the airframe, penetration of sound into the cabin from the engine/prop
and airflow over the airframe are three distinct effects and you need to use the proper
materials to control them. We have found the ordinary "foam rubber" and fiberglass
batting as supplied by the aircraft manufacturers to be virtually worthless.
"Super Soundproofing" Mat for Sound
It is a closed cell vinyl/nitrile insulating material which will not absorb water or oil.
Materials that absorb liquids are not suitable because if they get wet, they will
promote corrosion and increase their weight. The mat also conserves and blocks heat
because it is an insulator. It has fire retardant qualities and we have the
manufacturer's assurance that, in thicknesses over 1/8", it meets the requirements of
FAR 25.853b. Therefore, it is suitable for aircraft use.
It is available in 48" widths in thicknesses of 1/8, 1/4, 3/8, 1/2, 3/4 and 1 inch. It
may easily be cemented together to make other thicknesses.
The Noise Mat Barrier:
If one were to make a mat of sound absorbing material rather thicker and use a metal
barrier inside it, it would be very effective in really stopping engine noise coming
through the firewall. So if ordinary kitchen Reynolds Aluminum Foil is sandwiched
between the mats, (use contact cement), most of that noise will be prevented from
entering the cabin. A 2" minimum total thickness is recommended.
Finish Cloths and Vinyls: These are available from your local automotive upholstery
wholesaler in a myriad of thicknesses and colors. Most types of automotive materials
meet some auto industry inflammability requirements, but perhaps not specifically
those as applied to aviation. It is the duty of the installer to make sure that applicable
F.A.R.s are complied with.
For aircraft applications, you would be interested in thin vinyl materials such as used
for automobile headliners and durable cloths that have a thin foam backing. These
can easily be drawn tight and contact cemented to the above described
soundproofing mats (or metal backing panels), to produce very attractive,
professionally finished surfaces. The use of contact cement in spray cans simplifies
application. A heat gun (hair dryer) and some moisture will shrink out most wrinkles.
Other types of soundproofing materials.
A mention should be made here of some popular materials marketed by others. One is
a white foam material that is provided in a kit, specially cut for each aircraft it is
designed for.... It has contact cement on one side with a peel-off covering and comes
with a diagram as to where each piece fits into the aircraft. This is a very expensive
proposition because all this prep work has been done for you and you are charged
accordingly. A lot of time is wasted trying to find where each piece fits. These kits can
run up to $3000 per aircraft (and more) plus installation.
Another one is a lead-backed material developed for the military. It is so expensive
and heavy it would not be a contender for installation in light aircraft, even airliners,
even though it can sometimes be found surplus. Other materials are either not F.A.A.
approved, not closed cell material or are far more costly than our proven Super Sound
Proofing Mat! Check carefully before you buy!
Each aircraft has its "hot spots". That's certain areas where noise is the loudest. A
good soundproofing job would concentrate on these places that are the noisiest by
placing more material there. However, in general, the places in a light plane that
admit sound most readily are the firewall, cowl forward of the windshield/instrument
panel, kick panels, sidewalls of the cabin, roof and wing-roots. But the honor of the
most noisy goes to the windows! When replacing windows, use the thickest material
A thorough soundproofing job would place heavier layers of materials where the
sound was the loudest, near the front and lighter insulation aft. The entire cabin
should receive the treatment, above, below and all around including doors.
In an aircraft that has been flying, the best time to put in this material is when the
interior has been removed. Then it can be installed with a minimum of effort.
However, an installation can be made piecemeal. That is, section by section, as the
budget or time allows, with steadily improving results as more and more of the cabin
area is insulated. Some installers might do the doors on a weekend, the firewall on
another, etc. In all cases, investigate thoroughly for evidence of corrosion or other
damage before applying any batting that might cover it up.
While we cannot provide explicit instructions for each and every aircraft, we can give
you some general pointers to insure a good, effective job.
Installation; Soundproofing Mat
1. Cut your material to precise size and shape beginning with the largest
The material comes in different thicknesses to be cut to fit inside and to fill the
formers and frames, cabin sides and ceiling. (See diagrams). We do not recommend
using razor blades or knives. They will leave ragged edges. Cut it with an electric
knife, the kind that is used for carving turkeys. We use a Hamilton Beach battery powered
unit. These are inexpensive home appliance models. The rechargeable
feature is handy where an AC plug-in isn't available, such as out on the aircraft ramp
tie down area. Cut material a little over sized so that it fits inside the former or frame
with a push tight fit. It comes with a smooth "skin" side and a rougher side. Either
side can be cemented but the smooth side is more suitable. A dab of contact cement
here and there will ensure that it stays put, but it should fit well enough so that is
quite tight. If the area you are covering is rather large, apply a coating of Super
Sound Proofing Liquid and allow to dry first.
Use waterproof contact cement. Do not overdo the cementing because you may want
to remove the material someday to look for corrosion, run wires, etc. Use judicious
dabs of cement. Use a brush for this. You must put soundproofing every place where
the inside of the skin is exposed, especially on the firewall and inside the upper
instrument cowling and kick panel sides forward of the windshield. If it's difficult to
cut and fit the material directly because of obstructions, make a little cardboard
pattern by which to cut and fit the material.
Take your time. Don't get into a hurry. Make it fit as neatly as possible. It goes
without saying the material is to be installed only on the cabin side of the firewall! If
the firewall is covered with some kind of decorative mickey mouse firewall covering,
or fiberglass batting, remove it. It may then be reinstalled, but it's probably better to
just leave it off.
1. Use the bits and pieces left over to insulate the smaller remaining
Material can be contact cemented together to make larger pieces, so not much need
be wasted. Window frames and 'U' channels can simply be pushed full of the scraps.
Leftovers can also be used in the floor access panels by gluing them on the underside
of the covers, then reinstalling the panels and access covers. If you have some left
over, it's worth it to glue it to the inside of the belly access covers too. Every place
sound can enter should be covered as much as possible, but installing the material
everywhere inside the underside of the floor many times isn't practical. Don't worry,
even without that, the sound reduction will be very impressive. If your plane is apart
for repairs or overhaul, or an experimental under construction, a more complete job
can be done. However, do not overdo the gluing job. If you do, the material can be
difficult to remove if and when inspection is necessary in the future.
AN ALTERNATIVE METHOD OF INSTALLATION FOR EVEN GREATER
If your aircraft has 'snap-in' metal or fiberglass upholstery panels that are held in
frames, we have had great success with the following method which uses 1/2" or
thinner mat material:
1. Remove all such panels. Or, if you don't have them, make some.
Cut your mat materials a bit oversized. Then carefully cement a 1/2" layer of
material to the inside backside of the panel. Leave the edge of the soundproofing
around the edge slightly loose so that it can slide over the inside flange of the
mounting frame. Here, because these panels are nonstructural, and inspection won't
be necessary, a full even coating of contact cement on both the panel and mat and
then assembly will ensure that the material will not come loose, ever.
2. Cut and fit thinner insulation material to the inside skin areas same as the
application of the material detailed previously.
The idea here is to create a sound deadened boxed-in area with a dead-air space
between the two insulation layers. This is very effective and lighter, but requires
more time and effort.
For First Time Construction
1. Those of you building experimental aircraft will have good results by just using the
material on the inside of the cockpit area as explained. However, in addition,
if you wish to make removable upholstery panels as mentioned above, here's
1. Using either very thin aluminum sheet (.015" is a
1. good thickness), or very thin fiberglass sheet (some call it "tank Liner"), a bit
thicker, cut it to the size of the area you wish to cover. Don't try to make the
area to be covered too large or make the panel with curved edges or with
compound curves. The squarer, the better.
Pop rivet aluminum "T" "H" or "C" channel,
(obtainable from the Reynolds Aluminum stock rack at your favorite hardware store) to the
structure of the area that your panel will be mounted. Cut, fit and trim it so that a fairly loose
fit of all four sides of your panel is obtained. The channel you use must have a slot wide
enough that will accept the panel and the folded over upholstery material at its edge. It must
not fit so tightly that it can't be snapped in or out of place by bowing it. If needed, an
upholstery 'snap button' can be judiciously placed to hold it tightly.
Now, evenly glue 1/8" or 3/16" soundproofing mat to what is to be the front side of
the panel, leaving about an even 1/2" or 3/4" or so, open area up to the edges. This
will make a cushioned panel when covered with your automotive finish cloth or vinyl.
Lay this upholstery finish covering material over your panel, using it as a pattern and
cut it 2-3" oversize. Applying a coating of "Plio-Bond" (or several coats of contact
cement) to the metal or plastic then allowing it to dry, will provide a proper base for
gluing material to the back edge of your panel. Lay the panel, with soundproof mat
down, on the backside of the finish sheet and cement it down to the back of the
panel, pulling the wrinkles on the front out gently. Do not glue to the front at all. If
you start with the contact cement slightly wet, you can work out the wrinkles very
easily. When dry, trim the backside material away evenly and neatly with a razor
blade. Leave about 3/4" holding it. This creates a smooth, cushioned panel that will
snap into your aluminum frame very professionally, better than in factory planes!
You may use thin 1/8" foam rubber available from the upholstery shop instead of the
soundproof mat. Put the soundproof mat on the back side of the panel as explained
earlier or, even better, to both sides of your panel AND the inside structure for
additional "Super" soundproofing.
You can simply wrap the mat with your upholstery finish sheeting, just gluing it to
the back edge of the smooth backside, then gluing the panel in place. The spray on
kind of contact cement is very useful here. You can spray and attach it directly to the
smooth side if you wish. A little extra attention to the corners of your finish material
will be worthwhile for a neat job. A glue like "GOOP" works very well for this.
Larger Aircraft such as Airliners.
Cabin walls will need to be insulated thoroughly in the manner explained above.
Many times soundproofing of these types of aircraft is usually done perfunctorily by
workers who have no idea what it's all about. Without some knowledge and careful
attention to detail the consequence is a soundproofing job that is not very effective.
A Special Note About Helicopters
An application of the thickest material available (we can supply it up to 2" thick and
these thicknesses may be contact cemented together for even thicker) installed
between the rear cabin and engine/transmission will result in a definite, noticeable
noise reduction. Most of the time this is easy to do as these areas are usually quite
accessible. It may also be cemented to the inside upper bubble, seat backs and in the
underside floor areas for even better results. This may not have a totally silencing
effect on the flying noise, but can make conversation possible when on the ground
without having to reduce power or use the intercom. The best results will be had by
then cementing a layer of Reynolds Aluminum "Noise Barrier' into the mat as was
The Federal Trade Commission says that there are no existing test methods or
standards devised to prove the flammability of any material. Or are there accurate
indicators of the performance of cellular plastic materials under actual fire
conditions. Almost any material will burn under the "right" conditions. The test
procedures of F.A.R. 853.b, U.L. 94 or "Class A" are intended only as measurements
of the performance of materials under specific controlled conditions. These tests
generally mean the material will burn, but not support a flame, or will not support an
flame but will create smoke. You can get a good idea about any material you intend
to use by burning a scrap of it with a match. Materials used by aircraft
manufacturer's years ago may not even meet present day "standards." Generally, if a
person is responsible for returning a certified aircraft to service as a shop or
mechanic, he should use materials that are FAA approved and follow approved
procedures. If it is in the experimental category, you can use whatever you wish. For
certified aircraft, a letter is included here in this booklet certifying that it meets
requirements of F.A.R 25.853b(3). One may wish to place the letter in the aircraft
Sound Proofing Ratings. We haven't provided charts and graphs here because these
theoretical ratings are pretty much meaningless in the real world.
However, there are useful methods of judging the effectiveness of a soundproofing
material by measuring it's absorption and transmissibility properties.
Weight, How Far To Go
There is a weight penalty, of course. The Super Soundproofing Mat weighs
from .10 pound for the 1/8" to .7 pounds for the 1" material. (Per sq. ft.) A roll
of the popular 1/2" X 50' (200 sq. ft.) mat weighs about 50 Lbs. Obviously, if
you put it all in your plane, that's what the weight increase will be, less, of
course whatever you pulled out. Generally it takes about 3/4 of a roll of 1/2"
mat to do a good job on an aircraft such as a Cessna 182. (about 30 Lbs).
Such weights are not much of a consideration in a heavy twin, but can mean a lot in
an ultralight. Common sense counts here. If a few extra pounds of soundproofing,
perhaps even combined with an attractive interior offends your pocketbook or
sensibilities, perhaps an additional investment would be made in noise-canceling
headsets for everyone! In such a case, your wallet will be the one undergoing a
dramatic weight reduction! And you thought acoustical material was expensive!
Remember, headsets will not protect your hearing in the long term. In general, even
a little material is better than none. Here usually, more is better, is the rule.
MORE NOISE REDUCTION RECOMMENDATIONS
The neatness and care that is taken to ensure a good, tight fit and thorough application and
covering of the inside skin areas around the cabin will determine the effectiveness of your
soundproofing job. There is just so much you can do as a lot of sound is still going to come
in the windows. Flat acrylic sheets can be bought from a plastics wholesaler and cut to fit
much cheaper than buying pre-cut windows. Those of you that are building experimentals,
overhauling or rebuilding aircraft, should consider additional methods of sound reduction
i.e. replacing plexiglass windows and windshields with the thickest possible material available
(up to 3/8"). Our tests have shown that there is no advantage to using any thicker material.
Plexiglas edges of thicker plastic window material can be trimmed down with a router to still
fit in the original thinner frames and is well worth the extra trouble.
Also, a fiberglass firewall batting cover fitted on the engine side will also help quiet single
engine aircraft. This can be fabricated by your upholstery shop out of heat resistant
materials. Cutouts for wiring and other necessary openings through the firewall can be
closed by velcro fastenings and is well worth the additional cost and effort.
Loose fitting fairings causing gaps between the wing and fuselage in high wing aircraft can
generate lots of wind noise. This must be stopped. An easy way to do this is by using a
caulking gun filled with white weatherproof silicone caulk. (Use clear if your paint in that
area is not white!) For best results, apply it wet while the fuselage/wing joining cover is off.
Clean up with water. First tucking soundproofing mat firmly between the wing/root and the
fuselage will really help. This is usually not a problem in low wing planes, but should be
A noisy door because of a gap in its frame can mean the seal needs replacement or if the
door cannot be made to fit properly, (try some very careful bending!), perhaps even a
inflatable door seal. There are dealers for inflatable door seal kits for many types of aircraft
and such kits can be adapted to most others.
Super Sound Proofing Liquid!
This is a lightweight insulating material designed to add mass to metal surfaces
thereby reducing reverberant sound. Several coats can be built up to suit sound
proofing need. It also acts as a sound absorption/barrier where mat cannot be
applied. Use it in tail cones, under flooring panels, on firewalls and in corners mat
cannot go. Brush on, available in half-pints, pints, quarts and gallons.
Super Sound Proofing Flooring!
By popular demand, we are now making our flooring mat available. We've combined
a tough, wear resistant vinyl surface with a layer of closed cell foam to cushion and
isolate noise and vibration. It is designed for floorboards and firewalls in vehicles,
including aircraft. Thickness is about 1/4" and quite lightweight. It comes in 54"
widths by the running foot.
In any event, we're here to help you with any questions.
Addendum to "Soundproofing the Light
Aircraft" For Boats, RVs and Cars
The principles and applications described in the foregoing for aircraft are completely
applicable to other vehicles and even homes and offices. Absorption and blocking of
noise are the principles of most importance. How this is accomplished is a measure
of the effectiveness of the soundproofing job. First, we will discuss some specifics of
soundproofing certain kinds of vehicles and the specialties of noise reduction in the
business, shop, home or office.
In this application the two principle sound producing items are road noise and
engine noise. These are dealt with somewhat differently. However, in most cases the
method of absorption is used. The engine compartment usually has pretty good
noise blocking capabilities, so lining the compartment inside and out (where
practical) will do an excellent job. The hood is a particularly important place to start.
Factory material is usually not anywhere near adequate to do an acceptable
soundproofing job. The hood must be removed and thoroughly cleaned before
Road noise can be controlled by placing soundproofing mat on the firewall and
Flooring Mat on the floorboards, good coverage is essential. Mat can be cut into
squares and heated with a heat gun to help it conform to unusual shapes. Some
pretty expensive mat is available from some auto paint wholesalers called Dynamat.
Contact cement will hold it permanently in place. (Be sure its waterproof cement!).
The walls and roof should receive the treatment if practicable. Our Super
Soundproofing Mat is better for this as it comes in one piece instead of 12" squares.
Voids (open) areas can be closed up with expanding foam that is sold in cans. This
will cut down on an echoing effect. Be sure to do the trunk area as it will tend to
resonate like a drum into the passenger compartment from road noise. (Volvos are
notorious for this.) "Cadillac" quality comes from lots of soundproofing material and
attention to details of covering every square inch with material. Long distance
truckers can really benefit from soundproofing their cabs and sleepers and heavy
equipment operators will find fatigue greatly reduced as their noisy environment is
quieted! Again, a side benefit is the reduction of heat and cold.
Most noise is generated by the engine and carefully covering the engine compartment with
soundproofing mat will do a marvelous job of sound reduction. Soundproofing the engine
room walls and ceiling are most important in larger boats (ships), and hanging mats often
can often be very effective. More about that in the next section!
Other: Businesses, Shop, Home or Office
Businesses can really benefit by reducing noise pollution. Not only will workers, who
spend long hours in the same place every day, but customers (maybe more
importantly!) will really appreciate a quieter environment. Generally, annoying noise
in these areas is caused by machines or people. In an office or business, hard
reflective surfaces tend to severely accentuate noise. This is one reason why rugs
make a room quieter. Here, soundproofing mat can be placed in strips of one or two
feet high and run along the top of walls and even attached to ceilings for impressive
noise reduction. These sound absorption runners do a very effective job, the more
the better!! In noisy areas such as a shop, hanging barriers are made by attaching
soundproofing mat to plywood squares (both sides!), and suspending them between
the offensive noise producing machine and the receiver of the noise. This works
wonders. These barriers may be either permanent or temporary. If temporary, they
may be moved out of the way with some sort of wheels, hinge, cable or hook
arrangement. Temporary ones on casters are useful or suppressing grinding
machines or other loud noises that occur at different places around the shop. (Or, for
band practice in the garage!) Hanging squares are also effective in high noise areas
such as machinery rooms, pizza parlors, game rooms, halls, etc. They need not be
long or large enough to be very noticeable. Hang them from the ceiling in rows (at
least one foot tall), and notice how the quiet develops! We have acoustical foam
wedges, pyramids and for max sound control, anechoic wedges in blocks and
Contact us direct for help in other noise control situations, such as architectural
acoustics. We provide free consultation!
SUPER SOUNDPROOFING CO
P.O. Box 985
Vista, CA 92085
Tel: (760) 752-3030
Fax: (760) 752-3030
To The Pilot, Mechanic or Installer!!
Most of the materials mentioned are available
from a variety of sources, your common
hardware store has some of the items. The
SUPER SOUNDPROOFING MAT
is only available from us and:
AIRCRAFT SPRUCE & SPECIALTY
225 Airport Circle 91720
P.O. Box 4000 91718
Corona, CA. U.S.A.
Questions? Certs? We are happy to offer recommendations, advice, assistance and free
samples, or a hard copy of this booklet. Just call or write us.
Logbook Certification letter:
SUPER SOUNDPROOFING CO
Vista, CA 92084
September 3, 1996
RE: FAA CERTIFICATION OF "SUPER
To Whom it may Concern:
This letter provides information regarding Super Soundproofing Material for which
we are the mill distributors. This letter is to certify the material has FAA approval.
Our Super Soundproofing Material, is a vinyl-nitrile closed cell expanded foam. It
has been tested by an FAA approved laboratory that has determined the material, in
thicknesses over 1/8th inch meets, or exceeds, the flammability test criteria that is
contained in FAR 25.853(b). Results are available on request.
This material, in all thicknesses, meets various portions of U.L. Lab criteria
regarding different qualities and parts of D.O.T. "Proposed Guidelines for
Flammability and Smoke Emission Specifications."
In addition, the material meets MIL Spec. MIL-P-15280-H Form S. regardless of its
I herewith certify the above is true and correct.