Waterproof Microphones?

[envisionelec]

PUI makes some waterproof microphones tested to IP57.

POW-2242P-C3310-B-R

Digi-Key Part Number   668-1315-ND   

Disclaimer: I work for PUI. ** Edited, removed incorrect technical content.**
 

[CaptnYellowShirt]

PUI makes some waterproof microphones tested to IP57.

POW-2242P-C3310-B-R

Digi-Key Part Number   668-1315-ND   

Disclaimer: I work for PUI. Make sure you're sealing the rubber holder such that the rear of the mic isn't submerged in the liquid.

Oh wow. I'm glad you work for them. Time to get some grade A technical support.

I tried two of the closely related (?) POW-1644L in my initial experiment:


I was really disappointed they didn't work because everything else about them is perfect for my application.

Now I just took the mics and dropped them in a plastic cup of distilled water. But you're saying the rubber shroud seals the *back* of the mic. Like as if it were going to be placed tightly up against a PCB board?

Now if I epoxied or silicone sealed the back of the unit. Would that make it waterproof(ish) if I wanted to use it with wire leads?

[envisionelec]

PUI makes some waterproof microphones tested to IP57.

POW-2242P-C3310-B-R

Digi-Key Part Number   668-1315-ND   

Disclaimer: I work for PUI. Make sure you're sealing the rubber holder such that the rear of the mic isn't submerged in the liquid.

Oh wow. I'm glad you work for them. Time to get some grade A technical support.

I tried two of the closely related (?) POW-1644L in my initial experiment:


I was really disappointed they didn't work because everything else about them is perfect for my application.

Now I just took the mics and dropped them in a plastic cup of distilled water. But you're saying the rubber shroud seals the *back* of the mic. Like as if it were going to be placed tightly up against a PCB board?

Now if I epoxied or silicone sealed the back of the unit. Would that make it waterproof(ish) if I wanted to use it with wire leads?

The waterproof (designated by a 'W' as the third letter in the part number for our viewers playing along at home) is designed to be fully dunked, rear exposed and all for 30 minutes at 1m per the x7 in IP57. However (and as I learned after some internal discussions) our process of sealing the rear is unique and supposed to eliminate leakage completely. We're a bit surprised you're seeing a performance drop if the issue is indeed water penetration as both the Goretex 'felt' screen and the rear seal should prevent water ingress.

I would like to know more about your application. Please send an email with as many details as you care to share, including photos, to 'hammett(at)puiaudio(dot)com' and we'll tackle this issue head-on.

[CaptnYellowShirt]

Can do. Thanks for your help.

[PointyOintment]

In case that doesn't work out for some reason, I think carbon mics or fiber optic mics might be easy enough to waterproof. I'm pretty sure they can both respond to DC as well. A carbon mic might be harder to miniaturize, though. Wikipedia describes them.

If you want to go in a very different direction, you could try using fine-pitch bubble wrap as the transducer, with the volume of each bubble measured by an external (i.e. dry) optical device.

[Fraser]

The input from envisionelec just goes to prove how useful this forum is in connecting clever people with those with expertise in a particular area who can assist them....... well done PUI (envisionelec) 

[CaptnYellowShirt]

After several weeks of looking for a truly waterproof* subminiature microphone, I've concluded they don't really exist on the market. Many microphones exhibit some level of water resistance -- ones of minutes to hundreds of hours. However, for my application, I need a microphone that can resist water on the time scale of weeks to months.

For others who are interested, I've developed a method to waterproof these subminiature microphones. My tests have used the cheapest generic brands that DigiKey and Newark sell (e.g. $0.50/ea) and have achieved resistance to water, lightly salt water, IPA (20%), and soapy water. 

Contact me for details.


* Here I mean IP68, not IP67, when using the term waterproof (http://en.wikipedia.org/wiki/IP_Code). Personally, I'd consider IP67 (30mins) to be water resistant.

[envisionelec]

We can make an IP68 mic, but it's custom so you'll be looking at tooling costs for the felt and rubber boot. All things are possible...for a price.
Just putting that out there in case somebody comes across this thread and feels there isn't truly a solution to the issue.

[retrolefty]

Maybe hyrophones would be more appropriate?

https://www.google.com/search?q=hydrophone+frequency+range&rlz=1C1CHMO_enUS581US581&espv=2&tbm=isch&tbo=u&source=univ&sa=X&ei=ZlGPU4a0GdCiqAaVsILoBQ&ved=0CDQQsAQ&biw=1686&bih=900

[CaptnYellowShirt]

Maybe hyrophones would be more appropriate?

Sub-miniature? 4mm or less?

[CaptnYellowShirt]

I have sucessfully designed both.

Will you design either for under $5/ea?

[Richard Crowley]

Microphones are inherently designed to NOT be sensitive down to DC!  No conventional electret microphone, waterproof or not, will measure the steady-state pressure.  Perhaps a review of a couple of the basic fundamentals of microphones videos would be in order here.

You need a pressure transducer. Something that is designed to work down to DC.
For example: Freescale MPX4115 series transducers.
http://www.freescale.com/files/sensors/doc/data_sheet/MPX4115.pdf

I have seen examples of using these things with a flexible plastic tube attached and going down into the water (or whatever liquid) to measure the pressure at the end of the tube.  That way the transducer itself is never exposed to the liquid.

[CaptnYellowShirt]

I've been obtaining good results by modulating the current to the microphone -- on / off / on / off.

You can't resolve a typical spectrum from these types of measurements, as you're blanking out a good portion of your time history in periodic fashion. However, it does appear to remove the RC decay one would typically see when applying a static pressure to a microphone.

They didn't cover this method in those 'basic' videos you suggested. But hey, if you're an expert, I'd love to have you weigh in on why this may be working.

And as far as the tubes are concerned. The water/air/transducer interface that you're suggesting is horrible for measurement integrity and stability. You really need a 100% water/transducer interface that's been completely purged of air bubbles for good data.

[Richard Crowley]

I've been obtaining good results by modulating the current to the microphone -- on / off / on / off. ...
I'd love to have you weigh in on why this may be working.

Congratulations, you have re-invented "chopping"!     That was a technique used back a generation or two ago to handle DC values with circuits that otherwise worked only with AC signals.  By turning the microphone on and off, and as long as you can "calibrate" the results, then you can use that method as a crude pressure detector.  You may get even better results sealing the back of the electret capsule (as with RTV from a squeeze-tube) .

They didn't cover this method in those 'basic' videos you suggested. But hey, if you're an expert,

Mr. Ford mentioned putting a small hole in the rear of the capsule to equalize the pressure. He didn't make a big deal out of it, so it was probably easy to miss.. By sealing up this hole, the capsule becomes more sensitive to absolute pressure.  However, the diaphragm itself is still capacitively coupled to the internal amplifier, so it is not capable of sensing a steady-state pressure.

And as far as the tubes are concerned. The water/air/transducer interface that you're suggesting is horrible for measurement integrity and stability. You really need a 100% water/transducer interface that's been completely purged of air bubbles for good data.

It works in many cases. But not all cases. Since there are dozens of factors you didn't reveal here, we would have no way of knowing whether a specific solution would work in your (undefined) situation.