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'[OT] INVERTE THE WAVE'
2000\04\11@115347 by WF

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2000\04\11@172439 by hgraf

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>    A student is studyng how to invert some wave...
>
>    He intends to NULL some produced sound...in the factory that he works
have some TEXTIL >>>>>>machines and intends to reduce the noise produced by
them...applyng a inverted wave...
>
>    Does someone have some suggestions about this? Formula, site, etc...
>
>    I think that is too hard!

   An amp with a gain of -1? Although it will null the sound a little, very
rarely does the effect get good enough to totally NULL the sound. I have
been amazed by some of the noise canceling headphones in the store though.
TTYL

2000\04\11@184408 by Plunkett, Dennis

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{Quote hidden}

       To this I agree, as your student will need either the impulse
response or the fourier transform of the environment in which the machine
resides. All this is DSP type stuff, and will require several (Lots) of
measurements, as it is not just a simple task of invert the wave to cancell
it out, he will also have to remove harmonics and the like etc. Too much
stuff to go into for this list.

       Dennis
>

2000\04\11@195916 by Wagner Lipnharski

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Once installing a new electronic device at a noisy plant, I saw a group
of people studying how to reduce the ambient noise. Interesting point is
that most of the sound goes upward, since if reflects here and there but
there is plenty of empty space above, so a big part of it ends up going
to bounce at the ceilling and comming back directly to the people's
ears.  They installed cushion material at the ceilling, so no more
bouncing from the above. I remember it reduced tremendously the plant
noise.

Once at the new IBM building in Curitiba city (Brazil), it was installed
white noise generators to blast down room to room human voice.  White
noise is something your hearing can ignore, but it takes down a great
level of ambient sounds too.

Cancelling sounds with sounds, is the same as trying to eliminate the
concentric waves made by a rock in a lake, just using another rocks and
waves to cancel the original waves... icky, drastical things I don't
even want to think about.

I already saw a device to install in glass windows, reducing street
noise entering the room, works pretty well, but then, it is a different
story and the original sound is vibrating the glass, so it is not
difficult to cancel it...

Wagner

2000\04\11@210648 by Brandon, Tom

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Basic principal is to produce the same wave 180 degrees out of phase. Thus
the sound waves cancel in energy. http://www.headwize.com/ has some stuff on
Active Noise Reduction. In particular the article titled "Adaptive Active
Noise Control for Headphones Using the TMS320C30 DSP" is quite good. In this
article they describe the basic theory of Active Noise Reduction examine the
current (at the time) systems which are generally passive (non-adaptive)
algorithms and present an algorithm for Adaptive Noise Reduction. This is
basically a passive noise reduction system that looks at how much noise got
through (error) and uses this to adapt the algorithm. There system also
allows for selective Noise reduction (i.e. eliminate the jackhammer but keep
your coworker telling you you're about to be hit by a truck) but I don't
know that the algorithms for this are discussed in detail.

This article provides the DSP algorithms used by the system.

Tom.

{Original Message removed}

2000\04\12@062041 by Jinx

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From: Wagner Lipnharski
>
> Once at the new IBM building in Curitiba city (Brazil), it was installed
> white noise generators to blast down room to room human voice.  White
> noise is something your hearing can ignore, but it takes down a great
> level of ambient sounds too.

The same technique used to relieve tinnitus. The patient is fed white
noise, which they soon become used to and ignore. As the volume of the
white noise is gradually reduced over a period of time, it "takes" the
tinnitus with it as the patient's auditory system adjusts

2000\04\12@085851 by Alok Dubey

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again.. the voice is not predictable.. i have seen one application to hum
out a backgnd noise.. where our man sends a 180 deg out of phase wave.. but
it was predictable.. lotsa neural netwrk fundas would help in prediction..
Alok



> {Original Message removed}

2000\04\12@090710 by M. Adam Davis

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You will find that you have to apply the noise cancelling device either at the
point of the source, or the point of the reception.  Since you cannot apply it
at the source (unless you vibrate the entire machine at 180 degrees out of phase
with itself, or in other words, suppress the machine vibration), then you need
to do it at the point of reception.  This is why the noise cancelling earphones
work so well, they only have to deal with a point of entry.

The analogy of the rock on water is a good one.  Putting another speaker in the
factory with an inverted waveform next to the machine will cause another set of
waves.  Getting the radiation pattern of the waves to match and cancel is the
trick.  You will end up with peaks and troughs that are higher and lower than
the original sound, and some areas which stay level.  So as you move around the
factory floor, you'll percieve the machine louder and softer depending on where
you stand relative to the machine, relative to the speaker.

The other idea of using the window to suppress street sounds is also a good
example of suppressing the sound at a point.  Suppressing sound in open air,
however, is not practical using this method, if it is possible.

Instead, place sound deadening material around and on the machine, above and
below it.  Place the machine on dampeners so you aren't vibrating the factory
floor.  Make sure your rotating machinery is balanced (http://www.baladyne.com/
-put in a plug for the comapny I work for ;-) which can be a source of huge
amounts of vibration.

Give everyone earplugs...

-Adam

Hey! It compiles! Ship it!

{Quote hidden}

2000\04\12@092157 by M. Adam Davis

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Just had another thought.  One thing you can do to null out the sound is to
track everyone on the factory floor within earshot of the machine.  Once you
know their location to within a few inches (particularily the location of each
head, or even each ear) then you can solve a series of simultaneous equations
which will determine the phase of sound you should produce from a speaker near
the machine.  This equation will give the best noise dampening for each person,
given that a few aren't in optimal positions.

It occured to me as I was thinking about the program I am currently working on.
A long rotating shaft will have different unbalances along its length.
Balancing one point on the shaft affects the balance of all other points on the
shaft, so you need to find out how much each point affects the others, and then
solve a whole slew of simultaneous equatons to find the 'best' balance for every
point on the shaft.

Some people in the factory will be in optimal positions, but others will not.
You can find the best phase to output which will place each person as close as
possible to a nulled area of sound.

Of course, this will help a teeny bit, but sound bouncing around the factory
will also have to be nulled seperately.  In a completely deadened room this
would work beautifully.

Make it a bit more complex:  Space speakers above the factory floor every 20
feet or 4 meters.  then solve a series of simultaneous equations which deadens
sound even better.  You could almost create a sound curtain, such that
particular area in the factory is completely quiet, almost like being in an
office, but it is open air.  This solution would require several magnitudes
greater computer power than the suggestion above, but you may not need to deaden
the sound reflections as much, this system could handle them as well.  Not for
the faint of heart, the equations alone are mind bending, not to mention trying
to fit them in a computer, nevermind a DSP...

-Adam

{Quote hidden}

2000\04\12@093443 by Alok Dubey

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okay..now how do we shut down the soundthis query has made on the list
alok


{Quote hidden}

2000\04\12@132657 by William Chops Westfield

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   One thing you can do to null out the sound is to track everyone on the
   factory floor within earshot of the machine.  Once you know their
   location to within a few inches (particularily the location of each
   head, or even each ear) then you can solve a series of simultaneous
   equations which will determine the phase of sound you should produce
   from a speaker near the machine.  This equation will give the best noise
   dampening for each person, given that a few aren't in optimal positions.

Is this possible?  Ten or twenty years ago I would have labeled such a
suggestion as a obvious joke, but with todays gigaflop DSPs and what
not, it may have entered the realm of possibility.

It's a good idea in general to re-examine the set of dismissed
"impossible tasks" every couple of years to see if they've become
suddenly become possible due to technology advances.  I can see this all
the time in code at work - some bit of ugliness that was difficult to
make better, simply left that way, even after the infrastructure to do
away with the "ugly" part has been in place for a while.


BillW

2000\04\12@155903 by Andrew Kunz

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My problem is how to figure exactly how to balance a 12" rod 1/8" dia rotating
at 20K-30K RPM.

Andy









"M. Adam Davis" <EraseMEadavisspam_OUTspamTakeThisOuTUBASICS.COM> on 04/12/2000 09:18:11 AM

Please respond to pic microcontroller discussion list <PICLISTspamspam_OUTMITVMA.MIT.EDU>








To:      @spam@PICLISTKILLspamspamMITVMA.MIT.EDU

cc:      (bcc: Andrew Kunz/TDI_NOTES)



Subject: Re: [OT] INVERTE THE WAVE








Just had another thought.  One thing you can do to null out the sound is to
track everyone on the factory floor within earshot of the machine.  Once you
know their location to within a few inches (particularily the location of each
head, or even each ear) then you can solve a series of simultaneous equations
which will determine the phase of sound you should produce from a speaker near
the machine.  This equation will give the best noise dampening for each person,
given that a few aren't in optimal positions.

It occured to me as I was thinking about the program I am currently working on.
A long rotating shaft will have different unbalances along its length.
Balancing one point on the shaft affects the balance of all other points on the
shaft, so you need to find out how much each point affects the others, and then
solve a whole slew of simultaneous equatons to find the 'best' balance for every
point on the shaft.

Some people in the factory will be in optimal positions, but others will not.
You can find the best phase to output which will place each person as close as
possible to a nulled area of sound.

Of course, this will help a teeny bit, but sound bouncing around the factory
will also have to be nulled seperately.  In a completely deadened room this
would work beautifully.

Make it a bit more complex:  Space speakers above the factory floor every 20
feet or 4 meters.  then solve a series of simultaneous equations which deadens
sound even better.  You could almost create a sound curtain, such that
particular area in the factory is completely quiet, almost like being in an
office, but it is open air.  This solution would require several magnitudes
greater computer power than the suggestion above, but you may not need to deaden
the sound reflections as much, this system could handle them as well.  Not for
the faint of heart, the equations alone are mind bending, not to mention trying
to fit them in a computer, nevermind a DSP...

-Adam

{Quote hidden}

2000\04\12@162234 by David VanHorn

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At 03:55 PM 4/12/00 -0400, Andrew Kunz wrote:
>My problem is how to figure exactly how to balance a 12" rod 1/8" dia
rotating
>at 20K-30K RPM.

Two accelerometers, some math, and a yag laser.

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2000\04\12@162431 by M. Adam Davis

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Veeery carefully...  and in a concrete/cinderblock room with safety glass... ;-)

I assume this is a drive shaft on one of your boats?

-Adam

Andrew Kunz wrote:
>
> My problem is how to figure exactly how to balance a 12" rod 1/8" dia rotating
> at 20K-30K RPM.
>
> Andy

2000\04\12@180034 by M. Adam Davis

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At that point you need a stiff metal (titanium?) which was precision made
(extruded, rolled, milled, etc).  The stiffer the metal, the better anyway,
since you aren't losing as much energy in flexing the rod.  You could add
balancing mechanisms, but the added weight and cost are surely going to be more
costly than starting with a precision part in the first place.

BTW, why 1/8"?  Why not use 1/4", or even thick-wall tube at 1/4"?  Either of
these will certianly reduce vibration.

-Adam

Andrew Kunz wrote:
>
> My problem is how to figure exactly how to balance a 12" rod 1/8" dia rotating
> at 20K-30K RPM.
>
> Andy

2000\04\13@071259 by Andrew Kunz

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Yup.

What I do now is just get it as true as possible mechanically, and not worry
about it.  You can hear the difference, though, between drive shafts.

Andy











"M. Adam Davis" <KILLspamadavisKILLspamspamUBASICS.COM> on 04/12/2000 04:21:19 PM

Please respond to pic microcontroller discussion list <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>








To:      spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU

cc:      (bcc: Andrew Kunz/TDI_NOTES)



Subject: Re: [OT] INVERTE THE WAVE








Veeery carefully...  and in a concrete/cinderblock room with safety glass... ;-)

I assume this is a drive shaft on one of your boats?

-Adam

Andrew Kunz wrote:
>
> My problem is how to figure exactly how to balance a 12" rod 1/8" dia rotating
> at 20K-30K RPM.
>
> Andy

2000\04\13@072116 by Andrew Kunz

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The rod is a tempered steel.  Pretty tough.  I need to solder to it, so Ti is
out.

Go calculate how much energy it takes to buzz 1/8" steel at 500Hz at a 1/16"
amplitude and then tell me it doesn't matter!

1/8" for compatibility with the rest of the equipment (motor, prop, bushings,
bearings, etc).

Andy










"M. Adam Davis" <TakeThisOuTadavisEraseMEspamspam_OUTUBASICS.COM> on 04/12/2000 04:34:38 PM

Please respond to pic microcontroller discussion list <RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU>








To:      PICLISTEraseMEspam.....MITVMA.MIT.EDU

cc:      (bcc: Andrew Kunz/TDI_NOTES)



Subject: Re: [OT] INVERTE THE WAVE








At that point you need a stiff metal (titanium?) which was precision made
(extruded, rolled, milled, etc).  The stiffer the metal, the better anyway,
since you aren't losing as much energy in flexing the rod.  You could add
balancing mechanisms, but the added weight and cost are surely going to be more
costly than starting with a precision part in the first place.

BTW, why 1/8"?  Why not use 1/4", or even thick-wall tube at 1/4"?  Either of
these will certianly reduce vibration.

-Adam

Andrew Kunz wrote:
>
> My problem is how to figure exactly how to balance a 12" rod 1/8" dia rotating
> at 20K-30K RPM.
>
> Andy

2000\04\13@165712 by M. Adam Davis

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Check out the active noise control faq:
ftp://rtfm.mit.edu/pub/usenet/sci.answers/active-noise-control-faq
-Adam

{Quote hidden}

2000\04\14@004133 by Harold Hallikainen

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       This, of course, is really off topic! I've often wondered about this
noise reduction technique, though. It seems that unless the noise
cancelling source and the noise source are at the same location, you will
not be able to cancel the noise over a large area.It will be cancelled in
one location, but move just a little bit and the delays between the two
signals change and it's no longer cancelled. I've seen some stuff written
about noise cancellation, but don't see how it can work very well.
       Anyone have any more info?

Harold

On Tue, 11 Apr 2000 12:49:59 -0300 WF <EraseMEwfspamBLUSOFT.ORG.BR> writes:
{Quote hidden}

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2000\04\14@093723 by James R. Cunningham

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I don't have any technical info.  I can only say that it works very well indeed
in reducing the engine and wind noise that get through the headphones of my
plane.

Jim

Harold Hallikainen wrote:

> I've seen some stuff written
> about noise cancellation, but don't see how it can work very well.
>         Anyone have any more info?
>
> Harold

2000\04\18@104755 by Wagner Lipnharski

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The answer here is that if you have a single point where sound is
"tunneled", via a window, a headphone, even a hole in the wall, then you
can work out some noise cancelation technique, but it is very, very hard
to cancel noise in an open environment.   The similarity is that you
could control a "water wave" comming from a hole in the wall, but not
into the ocean.

"James R. Cunningham" wrote:
{Quote hidden}

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