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!

> WF wrote:
>
>     Hi,
>
>     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!
>
>     Miguel Wisintainer
>