Microphone Cleaning
Dave Martin
diaphragms on large diaphragm microphones. At the time, I didn't need to
know that, and only glanced at the post. However, I just got a 414 ULS,
and the diaphragm seems to be covered in dried spit. I'm hearing a
difference between that one and my other 414, and I think that a
cleaning is in order.
If someone could either re-post those instructions, or e-mail them to
me, I would be most appreciative.
Thanks,
Dave
Dave Martin Digital Media Associates
dave....@nashville.com P.O. Box 24525
(615) 228-7873 Nashville,TN 37202
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* CMPQwk #1.42 * UNREGISTERED EVALUATION COPY
Bruce Albertine
>A couple of weeks ago, someone posted instructions on cleaning
>diaphragms on large diaphragm microphones. At the time, I didn't need to
>know that, and only glanced at the post. However, I just got a 414 ULS,
>and the diaphragm seems to be covered in dried spit. I'm hearing a
>difference between that one and my other 414, and I think that a
>cleaning is in order.
>
>If someone could either re-post those instructions, or e-mail them to
>me, I would be most appreciative.
>
>Thanks,
>Dave
Dave...
I suggest you follow the post, written in response to the post you
mention and from a tech who worked at AKG for some years repairing mics.
His post made it clear that MICROPHONE DIAPHRAMS SHOULD NOT BE TOUCHED!!!
You can probably find the post if you browse back far enough, but I will
summarize it by saying that the membranes stretched across the diaphram
frames are very sensitive, and are mechanically "tuned" to achieve thier
response. Touching the membrane at all can significantly alter it's
"tuning", forever changing the sound of the mic.
The difference you're hearing between your mics is probably no greater
than the differences you'd hear between any two mics. You can buy brand
new mics of the same model, even sequential serial numbers, put them up
side by side, and hear interesting differences - mostly because of the
fragility of tuning those membranes.
Stains have been collecting on condensor mic diaphrams for decades and
there's no valid info suggesting these age stains have any significant
impact on the mics' performance. Certainly, the effects of cleaning
these diaphrams is far more drastic than the effect of some stains
collected over the years. Leave the mic alone or you'll probably ruin
it!
-BA
Monte P McGuire
Bruce Albertine <br...@vcnet.com> wrote:
>dave....@nashville.com (Dave Martin) wrote:
>>A couple of weeks ago, someone posted instructions on cleaning
>>diaphragms on large diaphragm microphones.
>>If someone could either re-post those instructions, or e-mail them to
>>me, I would be most appreciative.
>
>mention and from a tech who worked at AKG for some years repairing mics.
>His post made it clear that MICROPHONE DIAPHRAMS SHOULD NOT BE TOUCHED!!!
>Stains have been collecting on condensor mic diaphrams for decades and
>there's no valid info suggesting these age stains have any significant
>impact on the mics' performance. Certainly, the effects of cleaning
>these diaphrams is far more drastic than the effect of some stains
>collected over the years. Leave the mic alone or you'll probably ruin
>it!
I disagree completely that a lot of dried spittle has no effect on a
mike's performance. I have a pair of Beyer MC740 that now sound very
close to each other after cleaning a lot of gunk from one of the
mike's front diaphragm, so the difference is not all that subtle.
Obviously, it's best not to let spittle or smoke accumulate on
condenser mike capsules, but sometimes you inherit other people's
mistakes and carelessness. If the option is throwing the mike out,
having it rebuilt or cleaning it, then the risk of cleaning a capsule
isn't so great... If you fail, then you simply have it rebuilt like
you were going to do anyways.
So, I'll repost my article with the proviso that a) don't blame me if
you ruin your mikes, b) you may need to have the diaphragms or
capsules replaced to get them back to original performance levels and
c) you may completely ruin your mikes if you're careless or the
diaphragm is extremely thin.
Did I mention that you might ruin your mikes by cleaning them??
Here goes...
Funny you should ask... I spent the better part of an afternoon
cleaning the diaphragms of a pair of recently acquired used Beyer
MC740 mikes that had a pretty tough life. It's not all that difficult
to clean a condenser mike diaphragm, but it is risky; you have to have
extreme patience, good technique and the ability to risk total
destruction of the mike. Mistakes do happen and I've destroyed a mike
a long time ago while trying to clean it.
The basic technique is simple: take a Q tip swab and pull a small
flexible tuft of cotton about 1/2" long from the end of the swab. Wet
the swab with one of several solvents and gently scrub the diaphragm
with the flexible part of the cotton. You want to use as little force
as is needed to hold the swab against the diaphragm.
Surface tension is all the force needed to hold the wet swab against
the diaphragm; once the swab has contacted the diaphragm, you can
actually pull the swab away from the mike to reduce the force you're
applying. Initially, you want to try to lift off the dust instead of
scrubbing it around the diaphragm since it may scratch or tear the
diaphragm. Change swabs very frequently; the solvent may evaporate
quickly and the swab may become too dry to do anything useful. Swabs
and solvent are cheap... you don't want to scratch or tear the
diaphragm pushing dirt around, so change it often!
If you're simply removing dust or smoke contamination, Freon TF is the
best solvent to use since it is extremely gentle and it leaves no
residue. If you have dried spittle or other more tenacious
contaminants, you need to use a more powerful solvent, like isopropyl
alcohol (70% is fine) or water. Never directly apply solvent to the
capsule; if it leaks into the space between the diaphragm and the
backplate, the capsule could be ruined. Always apply solvent to the
capsule with a prepared swab; it must not be too wet, but more than
just moist. If it is too dry, the dirt will not dissolve in the
solvent and will be simply pushed around the diaphragm, probably
ruining it. If it's too moist, you could get excess solvent where it
shouldn't be and you may damage the mike.
On some mikes that use high impedance varnishes (like some flavors of
the 414), be careful not to get any solvent on the varnishes; they may
dissolve with the alcohol and really gunk up the capsule. I don't
know for sure about this possibility, but why risk it.
Whatever solvent you use, you should finish the cleaning with a pure
Freon TF cleaning so as to remove any subtle contamination that may
cause noise problems. If you prepare the Q tip and use spray can
Freon, you can rinse the Q tip while you're mostening it; the
resulting moistened swab will have extremely low residue.
I was able to clean all 4 diaphragms of the two mikes in about an hour
or two, working pretty slowly and cautiously. The difference in
performance was not very subtle; removing the considerable mass of
dried spittle from one of the mikes noticeably changed the HF
repsonse; the mike is now more bright and open and now both mikes work
very well as a stereo pair. They were useless before, so I guess I
won this time...
Best of luck (and don't blame me!!)
Monte McGuire - N1TBL mcg...@world.std.com
Corey Eng
the diaphram of his microphone, but to each his own. I am the former
AKG tech mentioned below. Maybe I should have been a little more
specific in saying that the CK12s (large diaphram capsule used in may
AKG mics) should never be touch (This also applys to any of the other
AKG condenser capusles) . My experience with other types of large
diaphram capsule is limited comparded to my knowledge of AKG
microphones, but generally they are all made the same way with the
same material.
I wish those who try clean their capsules luck.
One more thing some solvents will destory the gold which is "spudder"
on to the mylar. Be careful.
Later,
Corey Eng
Richard D Pierce
Stefan Heyer <he...@massive.aball.de> wrote:
>If microphone diaphragms are so fragile, can't they deteriorate
>just by aging and normal use?
In order to respond to high frequencies, the diaphragms must be extremely
light, thus they are susceptible to damage via mechanical means: shock,
mechanical distortion, misalignment, and so on
However, deterioration over time is generally caused by chemical means,
NOT mechanical. The materials used in making the diaphragms, then,
becomes an imprtant consideration, rather than how they are made or how
light they are.
The material used are generally very stable chemically. You'll find
aluminum, nickel, mylar, copper and other such materials used in
microphones. These materials are quite stable over time. Dynamic magnets
have shown problems with rust in the iron elements (due to improper
storage) and occasionally you'll find something growing on a material
(some fungi seem to love living on glass, sometimes found in the
insulators in microphones).
--
| Dick Pierce |
| Loudspeaker and Software Consulting |
| 17 Sartelle Street Pepperell, MA 01463 |
| (508) 433-9183 (Voice and FAX) |
David Josephson
doesn't seem to be doing so. I guess the thing that always gets me
riled is when people say stuff they know, or should know, isn't true.
Now, as in most fine polite circles, these things are said in order
not to offend, and the same is the case here.
>>If microphone diaphragms are so fragile, can't they deteriorate
>>just by aging and normal use?
Microphone diaphragms aren't so fragile(1). The big problem with this
issue is that most people don't know what's inside the microphone,
past the diaphragm, are terrified that they'll damage something, and
as a result get all spooky and do more damage than they otherwise
would. So they get shaky hands and oops, there goes the q-tip through
the diaphragm.
(1) Note, some early Neumann and AKG diaphragms were made of PVC rather
than PET and are subject to embrittlement due to loss of plasticizer
compounds. These diaphragms *are* fragile.
Microphones are cleaned all the time (when, and only when needed) _by
people who know what they are doing_ and can afford to make mistakes.
You have to allow yourself the mindset that if you break it, you can
afford to fix or replace it. Otherwise, leave it alone. The gap between
the diaphragm and the backplate varies from 10 microns to about 50
microns (that's 2/1000 of an inch maximum). Any pressure you put on
the diaphragm with any device like cotton, or a swab, will crash it into
the backplate. Get over it. So will a door slam, or a sharp snare drum
hit. If this causes damage, the diaphragm is already deteriorated to
the point where it can't be depended on for studio service. Make no
assumptions about the diaphragm unless you're able to check them yourself.
There is a lot of junk out there, particularly now that old studio mics
that were once tossed in a pile are worth $5000 and up. I have seen a
lot of mics that sellers claimed were "factory original" that were in
fact rather recently re-made (and the whole gamut from fraudulent junk
to factory-equal-or-better).
The accumulation of spittle and smoke on a large-diaphragm vocal mic
is often at least as heavy as the diaphragm itself. This causes readily
audible changes in response, and never (in my experience) for the better.
That it doesn't make it sound like an entirely different microphone is
proof that diaphragm mass isn't everything (in fact, the main controlling
component is the air cushion behind the diaphragm, but that's a topic
for another rant.) You need to remove this if the mic is going to sound
right. You also need to be sure that all external surfaces that may have
accumulated conductive deposits are clean so that you don't get fizzy
noises whenever the weather is damp.
Before you begin, scrub your hands absolutely clean with some harsh,
oil-removing soap. The object of the exercise is to avoid leaving
conductive or hydrophilic (water-attracting) deposits on the insulators.
My solvents of choice are isopropyl alcohol and distilled water. For really
awful cases, xylene is the backup solvent. I use a wooden-handled cotton
swab with an extra layer, about 1/2" thick, of long fiber cotton (rolled
cotton from the drugstore) wound on over the tip. Use a #2 or so sable
artists' watercolor brush, yes, the $20 kind, to remove the dust you can
brush off. Getting the brush a little damp by breathing on it will make more
dust stick to it. Almost all remaining deposits can be removed with just
water. Take your time, and keep the cotton wet but not dripping so you
have some control. When you think you have most of the junk off, STOP.
All solvents including the distilled water should be kept in tightly closed
bottles; pour out what you need into a cup and throw it out when you're
done. If the water isn't getting all the crud, add a little alcohol
(this is 91 or 99% isopropyl alcohol, with no other chemicals in it,
preferably lab technical grade at least but USP is good enough if at
least 91%) to the water, about 50% is usually enough. You use long fiber
cotton so you can see all the fibers you left behind, and remove them
before you reassemble the mic.
Often, you'll see some particle caught between the diaphragm and the
backplate. You have to make a decision -- are you going to tear the
whole capsule apart, or send it to a good mic lab, or buy a new one.
Most of the screwed-together mic capsules can be taken apart and put
back together with no special tools except screwdrivers that really
fit the screws, and pin wrenches that fit the threaded rings. Make a
drawing of how it came apart, it has to go back together the same
way. Measure the capacitances between each terminal and every other
terminal (for instance, a CK12 capsule has two diaphragms and two
backplates, that's four capacitances to measure) and confirm when you
put it back together than you're within a few percent of where you
started.
Modern diaphragms are made of mylar (PET, polyethylene terephthalate)
or PC (polycarbonate) and don't deteriorate much. However the metallization
may or may not be adhered well to the plastic. If you see pieces of it
coming off, or getting thin, STOP. A little missing gold won't hurt,
but if you lose some more it's not a microphone anymore. Metal diaphragm
mics use aluminum, nickel, stainless steel or titanium, all of which can
react with junk in the air to form corrosion products, which are often
conductive. If you see pinholes or cracks in the diaphragm, STOP, use
it as is if you can, otherwise get a new one.
Be patient, pay attention, take your time...
--
Josephson Engineering
Stefan Heyer
just by aging and normal use? I扉e heard stories about famous
engineers carrying decades - old microphones with them and i扉e
always wondered in what condition they are.
(Maybe we should create a myth about old diaphragms sounding
better than new ones, just like old stradivari violins. It might be
great fun to see it repeated everywhere)
Stefan
JKreines
I was about to post that Neumann used to recommend using a sable brush and
distilled water, which really did improve a filtht U67 I had... but you
wrote the book with your post.
FAQ it, someone!
Thanks,
Jeff