RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
Wax nostalgic about and learn from the history of early electronics. See articles
from Popular Electronics,
published October 1954 - April 1985. All copyrights are hereby acknowledged.
today's throw-away society, most people would never consider attempting
to repair a speaker if it were to develop a tear or a puncture.
Why should you bother when a replacement is so inexpensive? Well,
there are few reasons you might want to affect the repair yourself.
First, the speaker might be integrated into the system in such a
manner that replacing it would be difficult or even impossible.
Second, some speakers are actually pretty darn expensive, especially
large diameter models and high quality models regardless of size.
Third, a replacement might not be available, as with a vintage radio
or television. Fourth, maybe you just want the challenge and satisfaction
of repairing the speaker rather than adding its bulk to a landfill.
This article from Popular Science offers a short tutorial on loudspeaker
repairs. It was written before foam cones became available, but
adapting other repair media and adhesive for foam should not be
a big barrier to undertaking such a task. Be sure to choose a glue
type that exhibits some flexibility once cured, which means standard
cyanoacrylate (CA / superglue) would probably be a poor choice.
Special formulations for bonding foam are available and should work
There are a couple YouTube videos at the bottom of
the page demonstrating speaker repair.
a minimum of equipment you can correct many speaker defects by following
Loudspeaker defects are not too common
in present-day radio and television sets but occasionally they do
occur! When such faults crop up they are often due to carelessness
on the part of the hobbyist who accidentally pushes through the
fiber or pokes a hole in the cone itself.
Here are a few
of the more common loudspeaker defects which you will encounter,
along with the simple repair methods anyone can use to correct them.
Before we get too involved, the author wishes to point out that
he in no way encourages the repair of high-quality speakers, particularly
those that are used in today's high fidelity systems. Home repair
of speakers is usually a temporary expedient. Needless to say, to
restore a speaker to its original performance level it is advisable
to return the unit to the manufacturer for servicing.
voice coil lead: This defect will cause a "dead" set. The voice
coil leads are flexible wires between the loudspeaker frame and
the paper cone, and are located at the back of the speaker. See
Fig. 1. Breakage usually occurs either at the terminal on the loudspeaker
frame or at the connection point on the cone.
Repair a broken
lead by resoldering the connection. If the break has occurred at
the cone terminal, do the soldering job as quickly as possible to
avoid burning the paper cone. Use a hot, clean, well-tinned soldering
iron and rosin base flux.
Open cone seam: Loudspeaker cones
are of two general types - the seamless type which are molded, and
the formed type which have a cemented seam. Since the cement dries
out gradually, the seam on the latter type may open after a period
of several years. The loose edges may touch, causing a vibration
that produces a papery, rattling sound.
Fig. 1. Although only one is shown in photo, there are
two voice coil leads on every speaker, extending from speaker
frame to the cone.
Fig. 2. Correct method for applying cement to repair
an open seam on outer rim of speaker. Do not use speaker
until cement has hardened.
The remedy is to put fresh cement along the seam, as shown in
Fig. 2. General "loudspeaker cement," available at radio supply
stores, may be used for the job - or, if you prefer, you can use
Duco household cement. Don't use the loudspeaker until the cement
has had time to set thoroughly.
Torn cone: Tears in the paper
cone may cause symptoms similar to those encountered with an open
seam, and may also cause other types of distortion.
"puncture" tears will result when a sharp pencil or screwdriver
is pushed through the cone accidentally. These may be repaired simply
by brushing on cement, as shown in Fig. 3. Gently push the torn
edges together after applying the cement on both sides of the tear.
Longer tears may be repaired by patching with cement and cheese-cloth,
as shown in Fig. 4.
Fig. 3. Small punctures and tears in the speaker cone
may also be repaired by careful application of cement over
Fig. 4. Larger tears in the paper cone of the speaker
may be repaired by patching over with cheesecloth held in
place by cement.
If the tear is extensive, however, have a new cone installed.
This job is not too expensive, but does require a fair amount of
skill. It can be handled best by a professional.
voice coil: This is probably the most common loudspeaker defect.
If the voice coil is off center, it will rub against the pole piece
and field magnet, distorting the sound.
You can check for
this defect by holding the speaker by its edges and gently moving
the cone back and forth with your thumbs, as shown in Fig. 5. Use
only enough pressure to move the cone. If the cone is off center,
you can easily feel the voice coil rubbing against the magnet on
To re-center the cone and voice coil, you'll need
several thin shims. These can be purchased in sets at your radio
supply store and are available both in non-magnetic steel and in
fiber. You can also cut the shims from thin card stock if you do
not have the regular shim stock.
Fig. 5. Correct procedure for testing a speaker for
an off-center voice coil is shown in this photo. See text
for full details.
Fig. 6. To loosen the voice coil and cone assembly on
speakers that do not have a centering screw, apply solvent
to rim as shown.
On many old style speakers, a "centering screw" is provided.
This may be located either behind the magnet or in the middle of
the "spider" in the center of the cone. On most newer speakers,
no such adjustment is available and the whole voice coil and cone
assembly must be loosened by applying cement solvent. Use an eye-dropper
and brush to apply the solvent to the rim of the speaker, as shown
in Fig. 6. Apply solvent to the central dust felt also and remove
You'll have to wait a short while for the solvent
to loosen the cement before the cone can be freed. Proceed carefully
and do not try to remove the cone until it is entirely free. Otherwise,
the cone may be torn.
After loosening the cone assembly,
either by adjusting the centering screw or by using solvent, insert
three shims between the voice coil and the pole piece, as shown
in Fig. 7. The shims should be equally spaced around the pole piece
Fig. 7. After cone assembly has been loosened, insert
three shims between voice coil and pole piece. Shims must
be equally spaced.
Fig. 8. Final step is replacing the felt pad over the
speaker center by cementing it in place as shown. This pad
keeps out dust.
With the shims inserted, retighten the centering screw or re-cement
the cone. After the cement is thoroughly set, remove the shims carefully
by pulling up on them gently but firmly.
Complete the job
by cementing a new dust felt in place, as shown in Fig. 8. Exercise
every caution in using the tweezers, for a careless slip on your
part at this point could poke a nasty hole in the speaker cone and
provide you with more problems than when you started out.
Other defects: Sometimes the speaker frame will become bent
or warped, throwing the voice coil off center. This defect may often
be corrected by twisting the frame by hand in the direction opposite
the warp. In many cases, however, a new speaker must be installed.
An open voice coil winding requires a new cone assembly and
it is a good idea to have a professional repairman handle this job
Here are some YouTube videos for repairing
Posted October 25,
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