Microphone risk factors

"Average" quality -- cost and size being more significant criteria. (Think in terms of cell phones quality/cost/size)

What sorts of issues affect reliability, failure modes, etc.?

Any advantages to one technology over another? Any issues specifically related to MEMS devices?

Reply to
Don Y
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Noise floor is generally higher than electrets, but they are not significantly affected by high temperatures and humidity.

MEMS devices can often be reflow soldered. Electrets would depolarize if heated to such temperatures.

John

Reply to
jrwalliker

I spent ~5 hours at a buddy's studio, yesterday. As expected, he could tell me why he mic's the top hat with a different microphone than the kicker or the sax -- or the lead vocalist. And, what "justifies" the differences in costs.

But, it was virtually impossible to push him off the "recording music" application to think of the microphone as a "audio frequency sound pressure/vibration transducer".

E.g., when I asked him how he might *alter* his selection of microphones (assume still recording a particular artist/group) to do so OUTSIDE IN THE RAIN, he quickly fell behind the avoidance of "the band wouldn't want to PERFORM in the rain, let alone sit for a studio session in it!" I.e., he's too wed to the idea of human beings as being the source of the sounds he's capturing. So, assumes the environment is OBVIOUSLY going to be acceptable for COMFORTABLE human occupation (e.g., "STP").

"Lets assume a group *wanted* to be recorded in the rain. Are there any microphones you'd AVOID *using* in that environment? And, if so, why -- would they just perform poorly? Or, would they risk being irreversibly damaged?"

"If I wasn't planning on *using* them in the rain, but they happened to be left on an outdoor table/bench and it suddenly rained *on* them -- which would you regret most?"

"If the rain had broken but the air was still really humid, how does that affect the above?"

He finally offered that condenser mic's tend not to like humidity but that the effect is on performance and is temporary -- dry out the microphone (carefully!) and its no worse for the wear (though I suspect he doesn't REALLY believe this as he seemed hesitant to want to find himself in that situation!)

Rephrase the question with temperature: could I use these to record the sounds on the Antartic tundra? as its really cold, I probably wouldn't want to hang around while capturing those sounds -- could I leave the microphone set up for a month if I protected it from precipitation? would it see restored joy when it was finally warmed back up?

What if I *fastened* it to the underside of that cow bell so every time the bell was struck, *it* was (effectively) struck, even if indirectly?

What if I fastened a pair of them to the heads in my car and used them to monitor rocker arm/lifter noise? Would they be upset with the prolonged exposure to the heat of the engine compartment? Which technology would be LEAST upset?

He had nothing to offer on MEMS -- probably because it doesn't offer the predictable (as in "traditionally known") performance of the more established technologies. It would *seem* that it should be relatively durable. Yet, its not widely employed in the sorts of things that you might expect to find it due to its small size and level of integration. E.g., I think most (?) cell phones use electret condensers (though I haven't taken many

*different* makes/models apart to see how pervasive that claim).

What are the *downsides* of MEMS units?

What I'm looking for are guidelines that might be common to all such "transducers" with *specific* refinements that would apply to different technologies. Most of the information I've found specifies those refinements in terms of cost or

*signal* characteristics (use this for lots of dynamic range in signal; use that for a flat response; etc.)
Reply to
Don Y

The majority of condenser mic's use extrememly high impedance circuitry, even gigaohm resistors, so humidity is a problem. Low impedance RF based models exist and are favoured by outdoor wildlife and location sound people. Half an hour web browsing would be informative :)

Mobile phones now use MEM mics but I am not aware of "serious" audiophilic users of MEMs but I am not up to date. MEMs diaphragm capture area is very small.

piglet

Reply to
piglet

There are so many different factors that affect reliability that it's not possible to help without more information.

For example: Many of the tiny mics (including most MEMS devices) have very small holes for the sound to get in - they are very susceptable to dirt. A nice big traditional moving coil microphone with a 1.5" diameter is not much upset by mouse crap sized particles but may have other issues.

The MEMs mics are likely to be the most realible in terms of random failures in benign conditions (because of the very automated and controlled manufacturing process.)

So if you tell us what you want to do with it it may be possible to help.

MK

Reply to
Michael Kellett

You're looking at it the wrong way. I want to know what can possibly be done WITH a microphone as a cheap transducer to decide how I can apply them.

You'd like me to say "I want to deform a piece of metal; how can I do that?"

Ans:

- wack it with a hammer

- bend it with some pliers

- swage it in a hydraulic press

- heat it to its melting point and drape it over a form

- selectively add/remove material to affect the net deformation

I, instead, am saying, "Hammers are cheap. What sorts of things can I do with them? And, what are the things that will cause a hammer to fail or be contraindicated in a particular application." Ans: "You could use it to deform a piece of metal..." "You could use it as a paperweight..." "You could use it to drive a nail..." "You could use it as a tourniquet..."

[Ask yourself what uses you can devise for a microphone (or any other transducer of your choosing). If you can't come up with a dozen (or score), you're not trying!]

As I mentioned previously, a friend uses them in qualifying new engines -- "listen" for characteristic sounds of valve/lifter/rocker noises instead of pulling the valve covers off after every N hours of simulated wear.

Another firm has a device that uses a microphone to determine the structural integrity of telephone poles.

Putting a microphone on a hot engine block exposes it to a different set of stresses than holding it against a telephone pole.

Reply to
Don Y

it's

not

set

OK - I finally get what you are after but I'm not that interested in playing - I spent a fair chunk of my early engineering career designing and making microphones and that branched out into accelerometers and from there we moved into making knock sensors and supension control systems and then to shock recorders and then the company went bust (15 years ago) and I do other stuff now.

If I had a really good off the wall idea about using microphones I wouldn't share it here :-)

But - more seriously - the question is just too open.

The only slightly novel thing I've considered recently is using some cheapo ST MEMs mics with a frequency response up to 40kHz+ to make an anemometer.

MK

Reply to
Michael Kellett

You'll note I've not shared any of mine! :>

I'm not looking for ideas as to how to use them. I'm looking for general information of their vulnerabilities, contraindicators, etc.

E.g., I might come up with a great application but not be able to find an (affordable!) device that could operate in the constraints that the application dictates without damaging the "transducer".

So, I'm more looking for things like:

- microphones don't like getting wet

- microphones don't like being subjected to prolonged periods of high heat

- microphones subjected to frequent mechanical shock fail prematurely

- microphones don't like rapid temperature cycling etc.

The "typical" way of thinking of microphones is in conjunction with a human-oriented activity. So, they are specified for "human occupied environments" and applications that are more related to human hearing than as general purpose transducers.

E.g., I've a buddy with a recording studio who can tell me why each particular microphone is best suited (dollars vs. effectiveness) for each "sound source". But, completely helpless to tell me how those evaluations would change if I tweaked the environment: "What if I wanted to record a saxophone playing in a freezer?"

I don't want to pick a mic technology only to find that the common knowledge about it is useless outside of that *typical* application frame. Or, even approach a problem with an "audio" sensor if there are NO technologies that are suitable!

For example, when tablets are manufactured (by compressing "powdered granulation"), a common problem is air becoming entrapped in the "powder" as it is compressed. When the pressure is released, the compressed air causes the tablet to "explode" (the top pops off).

This could be sensed audibly by locating a microphone adjacent to the tablets' path of motion and listening to the sound that accompanies the release of the compressive force (heavy filtering but you *know* what the fundamental frequency of the signal is, a priori).

But, it would be an impractical environment as the inevitable accumulation of the powdered "granulation" would quickly render the microphone ("acoustical transducer") useless.

You'd never encounter this problem in a more traditional microphone application! :>

Reply to
Don Y

--------------

** Is this steaming great moron for real ??

FFS:

If you place a mic inside a plastic bag it becomes proof against moisture, water and dust. Sound transfers as usual.

If the environment is vibrating severely, mount the mic on a rubber isolator.

If it is absurdly cold, heat the mic with a resistor.

Wot a tedious, bloody TROLL !!!!

.... Phil

Reply to
Phil Allison

Separate the sensor and electronics. Sensor can be a robust piece of metal foil etc. Or even the material itself. Bounce a laser beam off of it to a photocell and "listen" for characteristic "sounds". Such a solution would be very inexpensive compared to traditional microphone technology and far less subject to the environment.

Reply to
Terry Newton

I am not very concerned with telling off the wall applicaions.

One is to come up with an array of microphones , hooked to amps and speake rs to make an active sound absorber. There are many restaurants that have such ambient noise that one can not talk to one's dinner companion. Not su re one could actually sell such things. I think the restaurant owners thi nk that lots of noise is a good thing. Could possibly be used for reductio n of noise in air planes or heavy trucks.

Another is using a mike at each end of a pole to make a directional sound sensor. Small market for locating earthquake victims and lost hikers. Pos sible replacement for shotgun mikes used for TV and movies.

Another is heterodyning ultrasonic sounds to audio frequencies for locating gas , air and steam leaks. Again not a large market. Could also be used for amusement in listening to bats.

And one last one is sensing intruders. Possible market is the wall between Mexico and the U.S. Think detection of tunnels being dug and primacord be ing used to make holes

Dan

Reply to
dcaster

In the above example, a microphone is impractical -- due to other constraints imposed by the application. E.g., the tabletting area has to be "cleanable" to ensure product from "tabletted compound X" doesn't contaminate "tabletted compound Y" (you wouldn't want the BABY ASPIRIN that you make in the afternoon to have traces of the VIAGRA that you made in the morning! :> )

So, any sensor in the tabletting area has to be cleanable. Does this require removing the sensor to clean it "off line"? Is the later (re)placement of the sensor critical (you wouldn't want to have to recalibrate things just because you removed a sensor!)?

Do you have to pot/encapsulate a portion of the sensor to make it cleanable? Does this further attenuate the signal you're trying to sense?

I posed this example to my recording studio friend as he'd seen one of these pieces of equipment "in action" in the lab on one of his visits. The tablet is formed between a pair of stainless steel "punches" while surrounded by a stainless steel "die" (imagine putting some powder in a tube and then compressing it *in* the tube by plunging pegs in each end of the tube; i.e., the tablet is surrounded by steel as it is being compressed -- several tons of pressure exerted in a millisecond or three).

You're surrounded by the noise of the mechanism (you're making 35-75 tablets concurrently) and trying to hear a little "pop" that is muffled inside a steel box -- that is MOVING past your sensor.

The analogy we came up with was mic'ing a kettle drum and recording its performances -- and, later, trying to decide *if* and *when* a grain of rice might have been on the membrane (detected by hearing the rice "bouncing" as the membrane is struck).

Had he a fair bit of experience in that application domain, he would have realized the dynamic range and sensitivity involved and would have "waved off" a microphonic solution.

Easier to have a component vendor characterize their components (e.g., sensors... microphones) than to educate the component vendor of the varied constraints imposed by the application and HOPE they can recommend something suitable! :>

Imagine having potentially dozens of different applications and having to bring a supplier (or ) up to speed on ALL of their constraints before they can offer a recommendation vs. letting THEM educate you on the capabilities/characteristics/liabilities associated with their "supplies"

(Most folks have experience in very few application domains)

Reply to
Don Y

On a sunny day (Sat, 13 May 2017 11:57:17 -0700) it happened Don Y wrote in :

Digital signal processing. The problem is not the mike.

You need the spectrum of the 'pop', do an FFT, and look for it.

There are other ways, train a neural net etc etc.

No mike is perfect. And this seems in the LF range, no wideband needed.

It is just a specific pressure wave,

But I do not want to start an in depth discussion about mikes, I had my part of that, worked in TV and film studio. Almost as many opinions as people. And I have no experience with MEMS mikes.

You could try learning to write some code. In C that is :-)

Endlessly babbling about it gets you nowhere.

Reply to
Jan Panteltje

.....

Isn't this a visual inspection issue? using a mic to hear a pop seems redundant when you can just look at it to see if it popped. But a laser-based sound sensor (if that's what you want) will be far more robust than anything with electronics where it needs to be cleaned. Just hose it off, no electronics to get wet.

Reply to
Terry Newton

They do. Actually, people like it too. It makes for more intimate conversation if the people at the next table aren't part of the conversation.

Sure, and it's don but the area where sound can be cancelled inversely related to frequency. Canceling engine noise is relatively east. Wind noise, not so much. ...unless, of course, the passengers are willing to wear headphones.

It's been done.

Also been done (many, many, times).

Reply to
krw

On a sunny day (Sat, 13 May 2017 19:12:08 GMT) it happened Jan Panteltje wrote in :

So this is how you _could_ go about it: Mount a microphone near that process, use one that is not obviously crap. Take your decent quality PC / laptop and record. Start you stopwatch watch and make a note of the times things go wrong (pop). Maybe MAKE things go wrong to get the pop sound.

Thank everyone, leave the mike in place, bolted or welded, create a job for somebody guarding it, contact the White House you created an other American job, also hire somebody to train these people who will in turn watch the microphone and prevent it from being moved or obstacles placed in front of it or it being used for other purposes. thank everybody again, and your president of course, go home, run your recording, do some FFT, look if you see a difference between 'plop' and normal 'pluff' sounds, if not contact everybody involved that more money and resources are needed. If there is a visible difference subtract the spectra, and use that as trigger for whatever, counter, activator, email, alarm, sprinkler, fire brigade, anti-terrorist squad, flashing lights, you name it. Homework, could be fun. Once you have the soft (IF you have the soft) then sell them your PC, train a user to configure it boot it, mail the White House again you created yet an other American job, and do not forget to _charge_ for it.

Solar cells sucking , what do you know.

Reply to
Jan Panteltje

On a sunny day (Sat, 13 May 2017 19:12:08 GMT) it happened Jan Panteltje wrote in :

PS I forgot the vow of silence, all operators should take one, and no farting either.

Reply to
Jan Panteltje

On a sunny day (Sun, 14 May 2017 09:17:05 GMT) it happened Jan Panteltje wrote in :

And, com to sink of it, I think it is best to use one of those parabola mikes, to get a narrow target beam, and mount it in a rubber mount against vibration, maybe hanging from the ceiling.

Reply to
Jan Panteltje

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