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Noise cancelling speakers?

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Anonymous
January 11, 2005 1:17:33 PM

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

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.
Anonymous
January 15, 2005 10:15:31 AM

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

"Remove the _" <n_e_i_l_w@n_e_t_l_i_b.com> wrote in message
news:cgSEd.9$ha.1@fe09.lga

> I've heard of noise cancelling headphones - but are there noise
> cancelling speakers? The ventillation ducts in my office create an
> annoying, constant woosh.

There might even be hidden speakers in the ceiling that are broadcasting
shaped noise to give that effect.

> 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.

It's called loud!
Anonymous
January 15, 2005 2:58:54 PM

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
Related resources
Anonymous
January 15, 2005 2:58:55 PM

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.
Anonymous
January 15, 2005 6:07:38 PM

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.
Anonymous
January 15, 2005 7:07:54 PM

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

>>
>>
>>
>>
>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.
>
>

Lotus was working 2on such a system. I don't know what became of it.
Richard H. Kuschel
"I canna change the law of physics."-----Scotty
Anonymous
March 6, 2005 8:22:57 AM

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.
>
>
>
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
Anonymous
March 6, 2005 2:37:02 PM

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
February 25, 2011 5:33:30 PM

They do make noise cancellation speaker systems for noise in ductwork generated by fan energy. if you are serious about the noise issue, my first response is get a HVAC mechanical engineer to look at the sound problem in person. He should be able to spot the source of noise generation and then make a determination about the sound source. Hissing means too high air velocity caused by several conditons. Fan generated noise is much harder to attenuate but it can be done several ways. I find it hard to believe that you want to use active noise cancellaiton as your first choise. There may be other problems with the system such as fan speed too high, wrong fittings in the ductwork, not enough diffusers for space, ducts too close to fan, etc.

for noise and vibration control, you may want to contact BRD Noise and Vibraton Control, Inc. if you are a large company and this is a real problem. BRD-nonoise.com



Jeff
Mechanical Engineer in Alabama
May 1, 2011 5:40:09 PM

If you amplify a sound and reproduce it out of phase, it will cancel.
Sounds a bit complicated for duct work.
Sounds like a job for a Duct mechanic.
September 23, 2011 5:45:44 PM

If you are dealing with a single frequency, then simple delay (by a half cycle) will produce out-of-phase. The problem, I imagine, is that noise typically has many frequencies, so each frequency needs different amounts of delay, so you can't just delay/invert the signal and play it through the speaker. You would need some multi-band approach. But I guess the headphone and car guys must have solved this.
!