Noise cancelling speakers?

Archived from groups: rec.audio.tech (More info?)

On Tue, 11 Jan 2005 10:17:33 -0500, "Remove the _"
<n_e_i_l_w@n_e_t_l_i_b.com> wrote:

>I've heard of noise cancelling headphones - but are there noise cancelling
>speakers? The ventillation ducts in my office create an annoying, constant
>woosh. Unfortunately it is completely out of my control. I was wondering
>if there was such a thing as speakers or a device that can neutralize the
>sound in some way. Thanks for any tips.

Pretty much impossible for your situation, although noise-cancelling
headphones would work.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Archived from groups: rec.audio.tech (More info?)

Remove the _ wrote:
> I've heard of noise cancelling headphones - but are there noise cancelling
> speakers? The ventillation ducts in my office create an annoying, constant
> woosh. Unfortunately it is completely out of my control. I was wondering
> if there was such a thing as speakers or a device that can neutralize the
> sound in some
> way. Thanks for any tips.
>
>
>
>
It's not just speakers you would need. I've heard of, but not heard,
systems that use a microphone to determine the exact noise being heard
and mask it with an out-of-phase signal, but I'll bet the cost would be
huge! That is if it would work at all in a free space environment, I
think the system I refer to was for cars, cancelling road noise.

Archived from groups: rec.audio.tech (More info?)

neilw wrote:
> I've heard of noise cancelling headphones - but are there noise
> cancelling speakers?

There are some specialized systems where a constant, predictable
noise (like from a big compressor or pump or blower, etc.)
can be cancelled with big speakers fed by an artifically-created
out-of-phase signal. But these must be designed into the system
and are rather expensive, so they are (were?) used only for very
special applications where the benefit outweighs the expense.

> The ventillation ducts in my office create an annoying, constant
> woosh. Unfortunately it is completely out of my control.

There have also been active noise-cancelling devices made for
HVAC ducts, but again, they must be designed into the system.

> I was wondering if there was such a thing as speakers or a
> device that can neutralize the sound in some way.

Alas, nothing practical that will work in the open air. The
"Cone of Silence" on "Get Smart" was a funny gag because
it never worked. But that part wasn't fictitious.

You could mask the sound (with your own local white-noise
generator), but that may be no better than the noise you are
complaining about(!) Or you can use headphones or earplugs.

Archived from groups: rec.audio.tech (More info?)

I guess a theoretical solution would be to record and isolate the noise you
dont want to hear, and reproduce it, phase inverted, with speakers that can
cover the band of the noise... You would have to place the speakers very
precisely, and probably play a little with the phasing, but i guess it could
work...

The theory behind this is that if you are capable of reproducing an exact
match at 180 degrees phasing, both signals should cancel each other...

Hugo

"Paul Guy" <mpaulmguym@meastlinkm.ca> wrote in message
news:g94l211rvugdb0hmjspml7g9ec0esr1eva@4ax.com...
> On Tue, 11 Jan 2005 10:17:33 -0500, "Remove the _"
> <n_e_i_l_w@n_e_t_l_i_b.com> wrote:
>
> >I've heard of noise cancelling headphones - but are there noise
cancelling
> >speakers? The ventillation ducts in my office create an annoying,
constant
> >woosh. Unfortunately it is completely out of my control. I was
wondering
> >if there was such a thing as speakers or a device that can neutralize the
> >sound in some
> >way. Thanks for any tips.
> >
> >
> >
> naaah...... forget about the electronic method, it only works
> effectively at very low frequencies, and has many trade-offs. It would
> be difficult or inneffective at the "hiss" frequencies that you are
> probably hearing.
> Instead, try to reduce the turbulence of the air flow. If you remove
> the air diffuser, you will get a more laminar (and quieter) flow.
> Unfortunately, if there is enough flow, you'll have serious draft
> problems in your office. Maybe jam a towel in it to reduce the
> airflow. Better yet, find a janitor or building technician to reduce
> the airflow at your end. If other people are on the same distribution
> duct, forget it! It is quite an art to match airflow throughout a
> building so you get the right degree of heat, cooling, and fresh air.
> Be happy you get fresh air.... in our building, the only fesh air is
> what comes in through your office door unless you are lucky enough to
> have an outside window.
> Try living with computers that have noisy hard disks that whine...
> If it gets real bothersome, try earplugs. You can get them to
> attenuate from a few db to about 30 db. You'll have to experiment with
> ones that are comfortable, and don't look weird.
>
> -Paul
>
> ..............................................................
> Paul Guy
> Somewhere in the Nova Scotia fog