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Smoke and Laser Microphone

09/18/2009 3:35 PM

Hello, all.

I'm a newbie here. The reason I joined is to gather feedback on the microphone design I've been working on. The new thing about it is that a moving stream of smoke or fog is used to replace the diaphragm or plate found in every other microphone. A laser beam penetrates the stream at a 90-degree angle and is received by a very fast PIN-type photocell (2 nanosecond rise time, 1.5 MHz bandwidth).

Sound pressure waves cause microscopic variations in the smoke stream, which scatter the laser beam. That scattering modulates the beam and the photocell's absorption to create an analog signal representing the original sound waves.

The U.S. patent, 7580533 can be downloaded for free from www.uspto.gov.

The audio quality of the first prototype is poor. I'm just happy it demonstrates the theory of operation. The next protos should be better. Since the smoke stream is very low mass and non-reactive, physically, this transducer has the potential to be sensitive and wide-band.

Cheers,

Dave

PS. Some very rudimentary models of the device are shown in YouTube clips. One of them is here:

Smoke n Laser Mic

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#1

Re: Smoke and Laser Microphone

09/18/2009 4:15 PM

Welcome to CR4 Dave.

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#2

Re: Smoke and Laser Microphone

09/18/2009 7:20 PM

Very interesting concept.

What exactly is the purpose for your new design?

Are you trying to make an improvement in the current audio recording technology?

Where/how can this new audio capture technology be implemented?

What are the advantages over the "standard" diaphragm microphones?

How would this type of Microphone compare to "traditional" Microphones for manufacturing/end user costs?

It seems like a very complicated design to accomplish the same task a relatively inexpensive/simple Microphone can do.

Quite Interesting... You have my attention.

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#10
In reply to #2

Re: Smoke and Laser Microphone

09/19/2009 2:29 PM

Hello again, RV. I'm not sure I had a point when I came up with the idea, other than it should be superior to other microphones from a theoretical POV. We'll see if it gets there. Cheers, Dave

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#3

Re: Smoke and Laser Microphone

09/18/2009 7:36 PM

Hi imon2nd,

Welcome! I'm sure there will be questions.

Now, how much better will your response be? How would it compare to a piezoelectric transducer on a rigid, stationary flat plate. How does that compare with the response of the rest of the system? Will loudspeakers be able to reproduce what you will record?

From the patent, "While sound waves travel in only one direction from the source".

What would that direction be? I'm having a problem with that, unless it is outward.

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#4
In reply to #3

Re: Smoke and Laser Microphone

09/18/2009 7:48 PM

I think a better wording might be... travels in ALL directions from the source. 360°

Or I suppose from the perspective of the microphone It would only be coming from the source... so it can be pinpointed to come from only one direction... until the waves begin bouncing off all nearby objects, which would cause it to come from multiple directions.

-But now I'm just Nitpicking

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#5
In reply to #4

Re: Smoke and Laser Microphone

09/18/2009 8:10 PM

That's really the problem. Pros use sound intensity probes at the source to analyze sound. It decays/reflects as soon as it leaves the vibrating source.

Worked at a place that did active noise cancellation.

Cheers!

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#9
In reply to #4

Re: Smoke and Laser Microphone

09/19/2009 2:27 PM

Right, RV. Sound leaves its source in all directions, but voice and musical instruments are directional, at least until the reflections kick in. Cheers, Dave

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#11
In reply to #3

Re: Smoke and Laser Microphone

09/19/2009 2:31 PM

Hello, Lynn. Fact is, we don't know how much better this thing will be than any conventional mic, diaphragm or plate based. On paper, it has tremendous potential along with some serious engineering challenges making to make it tiny. I'll publish performance results as they are developed. Cheers, Dave

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#15
In reply to #11

Re: Smoke and Laser Microphone

09/19/2009 4:00 PM

imon2nd,

Keep up the good work. Keep us posted. You could be on to something!

Lyn

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#35
In reply to #15

Re: Smoke and Laser Microphone

09/28/2009 10:35 AM

Hello, Lyn.

Thought you might be interested to know that a few days ago we figured out how to make the non-occluded-beam mode of operation work. All of the YouTube video clips to date show the first operating mode, occluded beam; the laser passes through the center of a ribbon of moving smoke. Sound pressure waves ripple the smoke, modulate the beam and the photocell tracks that effect to output an electrical signal analogous to the sound input.

That mode works well, but as many people have pointed out, the signal created by the smoke or fog stream itself is always present as a noise floor.

Now, in the second mode of operation the ribbon of smoke is located between the sound input aperture and the laser beam. The distance from the edge of the beam to the edge of the smoke stream is very small: about 0.01 inches. Sound pressure waves impinge on the beam only when there's sound input, yielding a signal. Otherwise, the laser beam-photocell "idle" signal is unaffected, resulting in a very low noise floor in the absence of sound. We hope to have a YouTube video clip online soon to demonstrate this.

Best Regards,

Dave

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#36
In reply to #35

Re: Smoke and Laser Microphone

09/28/2009 7:33 PM

Hi Dave,

That's great news. One more positive step. I'm sure we are all interested in this project's development and ultimate success.

Buy the way, I tried the Patent Office website and I couldn't get 7580533 to verify.

I Goggled it and looked at it on a free site. You gotta love those patent attorneys. They do have a way with words.

I wonder if rapid movement of the device has any influence on the position of the smoke ribbon, as a helium filled balloon moves in a closed car. Put brakes on: balloon goes backward? Maybe it's not an issue. Maybe you've already solved it, if it's a problem.

Keep us posted.

Lyn

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#6

Re: Smoke and Laser Microphone

09/18/2009 11:39 PM

Interesting, but what is the utility? Rescue work? Battlefield reconnaissance? It seems that outside of that lab this would be fraught with technical problems.

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#12
In reply to #6

Re: Smoke and Laser Microphone

09/19/2009 2:32 PM

Good point, capper. The utility of this thing will have to be proven. We'll see. Cheers, Dave

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#7

Re: Smoke and Laser Microphone

09/19/2009 10:31 AM

Seems a wonderful idea to me.Just this:i found in a phisics book :max.displacement of air particles at the minimun audible power(10**-16w/cm2):10**-8 cm.Smoke is heavier,so does it change something?length wave of laser maters?.Is there any easier explanation of your invention than get into USPTO?.-

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#13
In reply to #7

Re: Smoke and Laser Microphone

09/19/2009 2:36 PM

Hello, ferquiza. Yes, smoke, water vapor, glycerin fog, etc, all affect the speed of sound in air. We'll have to use DSP to compensate. I like water vapor as the medium, but it is really, really volatile. We've had trouble handling it in this app. Cheers, Dave

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#8

Re: Smoke and Laser Microphone

09/19/2009 1:06 PM

I can see a definite advantage to your microphone over any existing types. The elimination of a moving mass would greatly improve the quality of the frequency range. An opti-electronic system would not have any mechanical elements to degrade signal quality. It could definitely be a worthwhile mic for recordists.

Within the current spectrum of high fidelity sound, the two weak links are the microphone and the loudspeaker. They both suffer from the negative properties of mass as applied in a sound reproducing system. Theoretically, a sound curve should be a straight line. Deficiencies in reproduction causes dips and peaks on the ideal curve. These are caused by reluctance or resistance of a mass (ribbon, diaphragm) or suspension, coil, cone or ribbon of a loudspeaker.

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#14
In reply to #8

Re: Smoke and Laser Microphone

09/19/2009 2:37 PM

Thanks for "getting it" Ron. You see where I'm headed with this gadget. Not there yet, but working on it. Cheers, Dave

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#16

Re: Smoke and Laser Microphone

09/21/2009 3:31 AM

Interesting idea but I'm not sure how it could become a practical method for recording. Just imagine a singer or musician inside a room full of smoke/fog trying to perform. It would be rather imposible. And, of course, any movement of the performer would disturb the system producing unwanted "noise". Then you should use audio filters to choose the audio components e.t.c.... ...

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#17
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Re: Smoke and Laser Microphone

09/21/2009 7:59 AM

Goerge,

Did you watch the video? The smoke seems to be contained within a closed tube.

I'm sure imon2nd can explain.

I'm also sure that Les Paul got funny looks when he walked in with a 4x4 with guitar strings and a power cord, too. Today, electric guitars are ubiquitous.

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#18
In reply to #17

Re: Smoke and Laser Microphone

09/21/2009 10:57 AM

I have no access to YouTube through my company's PC. So, I didn't see the video. If it is as you said, I suspect that there is a small sound source inside the tube to create the sound waves. (It's not possible for outside sound waves to enter the inside of the tube.) I think that it is just an experimental prototype, so they don't care about the real conditions. However, in real conditions the sound source (i.e. the musician) must be in the same room with the "fog" (i.e. inside the fog). So, it cannot be practical, no matter how good performance this "microphone" has. Unless I miss sth.

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#20
In reply to #18

Re: Smoke and Laser Microphone

09/21/2009 11:05 AM

One more thing, George: there is no sound source inside the housing. The prototypes have a sound inlet hole in the side of the tubular housing. The hole is 5/16-inch in proto 1 and 1/2-inch diameter in proto 2. The hole has a very thin tissue paper cover (OK, I'll admit it; one ply of 2-ply toilet paper) to prevent fricatives and plosives from blowing the smoke stream out of the laser beam path. Cheers, Dave

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#19
In reply to #16

Re: Smoke and Laser Microphone

09/21/2009 10:58 AM

Hello, George. The current prototypes are open; the smoke is dispersed out the top of the unit. In a commercial version of this thing, assuming we get there, the smoke or fog would be fully contained in a closed loop recirculating system. Alternatively, the medium could be in cartridges and a disposable filter would be used to capture "used" medium. We have tried water vapor as the medium and it does work. I think it would be harmless to vent water fog out of the mic. In any case, the amount of medium expelled is very small for any type of fog or smoke. For more details, download the patent, it's free (the copy, not a license). Best Regards, Dave

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#25
In reply to #19

Re: Smoke and Laser Microphone

09/23/2009 4:23 AM

If the "fog" is contained inside a closed area (e.g. a tube) in order not to be expeled (and not needed to be produced continually) then you have to use a kind of "diaphragm" (e.g. the tissue that you used in your prototype). This should permit the sound to enter the tube and "modulate" the fog and it should, also, prevent the fog from being expeled from the tube. However, this "diaphragm" have its own bandwidth (resonation e.t.c.) and changes the original sound. And this "altered sound", finally, modulates the fog. In this way, the advantage of this microphone -which is the high bandwidth and high quality- is not valid any more. Have you thought of this???

Nevertheless, its a quite interesting project and I wish you good luck with the commercial application.

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#26
In reply to #25

Re: Smoke and Laser Microphone

09/23/2009 4:27 AM

Hello?

"Hello, George. The current prototypes are open"

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#28
In reply to #26

Re: Smoke and Laser Microphone

09/23/2009 10:56 AM

Hi lynlynch. The current prototype is open but in a commercial application I think that the device must be closed. Otherwise it will smoke like "chimney". I, also, suspect that the flow of the fog (e.g. whirl) may disturb the proper "modulation" producing noise. And, of course, if it is closed then it will not have to produce fog all the time. (It will produce just the proper amount of fog in the begining and it will keep it inside). So, it has to be closed. But then, there must be a kind of "diaphragm" (as I refered to my previous post) with a degradation of the performance of the microphone.

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#31
In reply to #28

Re: Smoke and Laser Microphone

09/23/2009 4:33 PM

Hi GK,

I don't know enough about this thing to have an opinion, yet. I do agree that a physical barrier would have an effect. I'm just listening mostly.

Cheers.

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#32
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Re: Smoke and Laser Microphone

09/23/2009 4:42 PM

A physical barrier may not have an effect if outside the stream parameters.

No more than a spectator...like me

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#33
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Re: Smoke and Laser Microphone

09/23/2009 4:47 PM

You could be right. I guess it would depend on the response of the film, etc.

I'll just sit on the sidelines with you, if you don't mind the company.

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#34
In reply to #33

Re: Smoke and Laser Microphone

09/23/2009 5:10 PM

Hey, just dont start taking up my elbow room.

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#27
In reply to #25

Re: Smoke and Laser Microphone

09/23/2009 10:46 AM

George, We've run Proto One and Proto Two with open sound apertures as well as lightly covered with a "pop" screen (one ply of two-ply toilet paper), which does nothing much to attenuate sound. It only removes the puffs of air from fricative and plosive parts of speech. I imagine there will be both fully open and screened versions of this mic technology in commercial applications. In no case will there be anything that acts like a diaphragm in the core transducer area. Thanks for the best wishes, and... Best Regards, Dave

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#29
In reply to #27

Re: Smoke and Laser Microphone

09/23/2009 11:27 AM

Sorry, Dave. I wrote and sent my previous post before seeing your post. (We were writing almost at the same time.) I think that the thin toilet paper doesn't keep the "fog" inside the device effectively. In the final product -probably- you have to use sth more solid (at least at your "screened version"). This will act (unavoidably) as a kind of "diaphragm". So, you have to pay attention on this material: solid enough to keep the "fog" inside the device... but not too solid, permitting the sound to enter the device (foggy area) undisturbed... (I think that you got my point)...

Best regards

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#30
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Re: Smoke and Laser Microphone

09/23/2009 12:35 PM

George; Your point is certainly valid and is a design factor. One thing I'd like to point out is, the fog or smoke is constrained by aerodynamic factors to a small vertical flow, surrounded by "clean" air, which is also moving at the same velocity. To the naked eye, the ribbon of smoke looks almost solid and very distinct. It is relatively resistant to lateral movement due to its speed. That ribbon of fog or smoke acts kind of like a diaphragm; one with very little mass. I admit, we do not completely understand the interaction between the sound pressure waves and the smoke ribbon. The physics involved are complex. The principal mechanism of modulation may differ with laser wavelength versus particle size. Best Regards, Dave

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#21

Re: Smoke and Laser Microphone

09/21/2009 2:45 PM

I am still in doubt about the same: if two peaks of power of the light beam have double frequency than light signal,course, the lengthwave related and its relation with the stream column displacement, both in same order of magnitude, determines, i guess,a high noise level.Not distorted signal but noisy.Is posible solve this problem in case it is as i think, using diferents beams or spliting the same and many known tricks commonly used in electronics.But is this the case? Am i wright?.In a different order of questions:need to be laser light? need to be monocromattic light? need to be coherent light? what is "DSP"?

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#22
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Re: Smoke and Laser Microphone

09/21/2009 2:59 PM

Hello, Ferquiza. Yes, the light must be coherent and monochromatic: a laser. We're using a red laser at a wavelength of 650 nm. The smoke/air stream is rippled or sequentially compressed by sound pressure. That scatters the laser beam. Yes, the noise floor is high because the smoke is somewhat chaotic within the laminar flow. The good news is, the noise is "white." Presently, we have 6 dB of noise and 36 dB of signal above that. We expect to improve this tremendously over the next year. Bear in mind, we have only completed one prototype and are working on the second. DSP = Digital Signal Processing; a field I have worked in for 26 years. Stay tuned. We'll be producing a video this week in which I will disassemble Prototype Two and discuss the various features and problems of each component. Best Regards, Dave

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#23

Re: Smoke and Laser Microphone

09/21/2009 10:02 PM

Hi imon2nd,

You should add a mirror or two, then your invention would be magic (operation with smoke & mirrors) . Just don't let the smoke out - that's how resistors die.

-S

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#24
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Re: Smoke and Laser Microphone

09/21/2009 10:59 PM

Hello, StandardsGuy.

Whoops, we did let some smoke out. That would explain a few things.

About the mirrors--I'm sure you know they are inside the laser unit. We try not to mention them for the obvious humor that would result.

Best Regards,

Dave

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#37
In reply to #24

Re: Smoke and Laser Microphone

12/05/2009 9:18 PM

I must say that this is a very intereseting concept. I remeber reading about laser microphone technology a few years ago and began to ponder it today. I did not realize that it had become so widespread. I work in a recording studio and have experimented with many methods of recording through various microphone techniques. I have reversed the polarity of a speaker and used it as a mic which actually creates an interesting mic technique. i have also taken apart an old crt television and revesed the polarity of its speakers and sent their outputs to the horizontal and vertical coils which produce the images. This was more for visual purposes. I am interested in trying the laer mic technique. If perfected it could eliminate many phase and nosie crossover problems that occur with traditional microphones. Why not try reflecting a signal off of a piece of glass with foam glued to the back of it or maybe acoustical fiberglass. The smoke in the bottle mic is interesting to me because it could be used for surround sound applications if you output to 7.1 channels for instance. You could have a 360 degree panoramic mic without phase cancellation i suppose. It seems that these laser mics stop at 300Hz is there any way to pickup more bass down to 20Hz by chance. I am going to build one and experiment with it asap. The possibilites behind this concept are very intriguing and i am curious to see what could be done with polarized wave length recordings and so fourth. Very cool concept.

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#38
In reply to #37

Re: Smoke and Laser Microphone

12/06/2009 4:27 PM

Hello, Calypso.

I'll be interested to hear about your experiments with the smoke and laser microphone concept. You're welcome to download design information from my website:

http://www.schwartz-engineering-design.com

Best Regards,

David

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#39
In reply to #38

Re: Smoke and Laser Microphone

12/07/2009 2:31 AM

Awesome thanks. i just watched you and your sons videos on youtube and im quite amazed. Im going to check out the design info next. I would like to experiment with other elements besides smoke as well. Have you ever tried gasses such as Co2? I am going to try a number of things in different ways. I am particularly thinking of using a liquid metal called gallium in a bowl and reflecting it from that to a photocell and also other dense liquids such as cooking oil of which i could use to suspend a photocell inside of. do i need a photocell like this http://www.lightbulbsdirect.com/page/001/PROD/T368, this https://lightsonrus.com/store/products/Intermatic-Stem-Mount-with-Swivel-Photo-Control-208%252d277VAC-%252d-K4253.html, or this, http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&pa=202420&productId=202420&keyCode=WSF&cid=GMC

? How does the audio look on a spectrum analyzer for you David? Do you preamp, eq, or compress the signal? Once i get through my final exams this week im going to jump on this project, I already told the other engineer at the studio about it and he's stoked. oh and btw im a Schwarz as well.

Keep on tweaking knobs,

-Wes

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#40
In reply to #39

Re: Smoke and Laser Microphone

12/07/2009 5:42 PM

Wes;

One of the very first microphones ever made used a little pool of water and a needle. I think Wikipedia's article on microphones discusses it. Liquids are generally non-compressible so you would be looking at second order effects to get audio out.

The info on the photo detectors we've been using is on my website. One of them is a Thorlabs PLA100A, which has an integrated preamp of mediocre quality.

For our PFD Mic, we've used water vapor as well as various different types of synthetic smoke. A colored gas would work, like Chlorine, but the toxic side effects would be unfortunate.

Cheers,

David

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Anonymous Poster (1); bwire (1); calypsobomber (1); ferquiza (2); G.K. (5); imon2nd (15); lyn (8); rcapper (1); ronseto (1); RVZ717 (3); StandardsGuy (1); stevem (1)

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