[Knack]

We currently have one of the quietest ceiling fan models in our bedroom, but
I'm wondering if I can suppress that fan noise even further. However, we
don't want to wear earplugs or noise-cancelling headphones while we sleep.

Just an idea-- Was wondering if it could be possible to somehow make the
sensor and signal processor of one of those noise-canceling headphones (For
example, Panasonic RP-HC500) drive a larger amplifier, which would in turn
power a pair of small cheap PC type speakers. The little speakers could then
be spaced apart above the headboard of our bed.

Was hoping that I could obtain all components that I need (except the
RP-HC500 and the PC speakers) at Radio Shack or some other local electronics
components retailer. However, I'm not an electronics tinkerer so I have no
clue as to what the specs would be for those components.

From school (long ago) I have a vague and very limited knowledge of
electronics (Ohm's law, impedence matching), but know nothing about
amplifiers and next to nothing about filters/tuners.

Don't want to spend more than a total of US$400 on this. Is the idea
feasible? If so, then if someone could give me some tips/steering about the
specifics of what I would need, then I'd be greatly appreciative.

[Kevin McMurtrie]

In article ,
"Knack" wrote:

We currently have one of the quietest ceiling fan models in our bedroom, but
I'm wondering if I can suppress that fan noise even further. However, we
don't want to wear earplugs or noise-cancelling headphones while we sleep.

Just an idea-- Was wondering if it could be possible to somehow make the
sensor and signal processor of one of those noise-canceling headphones (For
example, Panasonic RP-HC500) drive a larger amplifier, which would in turn
power a pair of small cheap PC type speakers. The little speakers could then
be spaced apart above the headboard of our bed.

Was hoping that I could obtain all components that I need (except the
RP-HC500 and the PC speakers) at Radio Shack or some other local electronics
components retailer. However, I'm not an electronics tinkerer so I have no
clue as to what the specs would be for those components.

From school (long ago) I have a vague and very limited knowledge of
electronics (Ohm's law, impedence matching), but know nothing about
amplifiers and next to nothing about filters/tuners.

Don't want to spend more than a total of US$400 on this. Is the idea
feasible? If so, then if someone could give me some tips/steering about the
specifics of what I would need, then I'd be greatly appreciative.

The area covered by simple noise cancellation is inversely proportional
to the frequency. Canceling noise in part of a bedroom probably
wouldn't work above 80Hz. This is why noise cancelation works great for
headphones but not for rooms.

My previous car had active noise cancellation for the low frequency
engine drone. Even that didn't work so well because it caused
mechanical rattles in panels near the speakers.

[Eeyore]

Knack wrote:

We currently have one of the quietest ceiling fan models in our bedroom, but
I'm wondering if I can suppress that fan noise even further. However, we
don't want to wear earplugs or noise-cancelling headphones while we sleep.

Just an idea-- Was wondering if it could be possible to somehow make the
sensor and signal processor of one of those noise-canceling headphones (For
example, Panasonic RP-HC500) drive a larger amplifier, which would in turn
power a pair of small cheap PC type speakers. The little speakers could then
be spaced apart above the headboard of our bed.

No. It won't work. You can only ever meaningfully cancel sound over a tiny area
(volume).

Graham

[Greg Locock]

Eeyore wrote in
:


No. It won't work. You can only ever meaningfully cancel sound over a
tiny area (volume).


Such as the entire cabin of a passenger aircraft, or in some circumstances
even a car park or a harbour- if you can superimpose the correcting source
and he original.

'tiny' beng a somewhat loose term.

Cheers

Greg Locock

[Richard Crowley]

"Greg Locock" wrote ...
Eeyore wrote :
No. It won't work. You can only ever meaningfully cancel
sound over a tiny area (volume).


Such as the entire cabin of a passenger aircraft,

For low frequencies, perhaps. See the other posting on
first-hand experience with active noise cancellation in his
vehicle.

or in some circumstances even a car park or a harbour-
if you can superimpose the correcting source
and he original.

If you can actively counteract the noise at the source (as
an enclosure around a generator, etc.) perhaps. Only a
very limited cases of effective application, at least at this
stage of development.

If the OP wanted to make a PhD thesis out of the experiment,
it might be interesting, but I wouldn't bet any $$ on it.

[[email protected]]

On Sep 15, 6:09 pm, Greg Locock wrote:
Eeyore wrote :

No. It won't work. You can only ever meaningfully cancel sound over a
tiny area (volume).

Such as the entire cabin of a passenger aircraft, or in
some circumstances even a car park or a harbour-
if you can superimpose the correcting source
and he original.

'tiny' beng a somewhat loose term.

Well, even by your own somewhat extraordinary claim, "tiny"
is, in fact, a pretty well defined term: you defined it:

You state it can be done "if you can superimpose the
correcting source and he [sic] original." Fine. So let's
superimpose the original (4 engines on a 747 along
with the entire outside skin of the plane which is where
most of the in-flight noise due to turbulence comes from.

Now, using YOUR proposal, please explain to the gathered
audience how you would "superimpose the correcting
source and the original.) The original noise source is
the size of a 747. According to you, if you can superimpose
a second, out-of-phase 747-sized noise source on the
original you're done. So then only place I can put the
correcting source is NEXT to the 747, say at an average
distance of 100 feet, and place the person awaiting the
sonic remedy exactly in between the two.

And how's that working out for you?

The problem with your rather extraordinary claim is that
in an airplane cabin, there is no single "noise source:"
it's all over the place and highly uncorrelated. I can correct
is over a very small area, to the limits of the wavelength
desired whicyh is defined by the highest frequency I
want to cancel, and that is a VERY precise definition of
"tiny."

[just wondering]

"Knack" wrote in
:

We currently have one of the quietest ceiling fan models in our
bedroom, but I'm wondering if I can suppress that fan noise even
further. However, we don't want to wear earplugs or noise-cancelling
headphones while we sleep.

Just an idea-- Was wondering if it could be possible to somehow make
the sensor and signal processor of one of those noise-canceling
headphones (For example, Panasonic RP-HC500) drive a larger amplifier,
which would in turn power a pair of small cheap PC type speakers. The
little speakers could then be spaced apart above the headboard of our
bed.

Was hoping that I could obtain all components that I need (except the
RP-HC500 and the PC speakers) at Radio Shack or some other local
electronics components retailer. However, I'm not an electronics
tinkerer so I have no clue as to what the specs would be for those
components.

From school (long ago) I have a vague and very limited knowledge of
electronics (Ohm's law, impedence matching), but know nothing about
amplifiers and next to nothing about filters/tuners.

Don't want to spend more than a total of US$400 on this. Is the idea
feasible? If so, then if someone could give me some tips/steering
about the specifics of what I would need, then I'd be greatly
appreciative.



Just to bring some sanity to the discussion, let me point out that what
can vs can not be done will depend on the characterstic of the fan noise
that you want to cancel. Since you don't give any detials, there really
is no difinitive answer. Perhaps the fan motor is coupling 120Hz to the
ceiling structure and the ceiling is acting as a sound board. If this is
the case, mechanically isolating the fan would help. An alternative to
active noise cancellation would be to reduce the speed of the fan.

[Eeyore]

Greg Locock wrote:

Eeyore wrote

No. It won't work. You can only ever meaningfully cancel sound over a
tiny area (volume).

Such as the entire cabin of a passenger aircraft, or in some circumstances
even a car park or a harbour- if you can superimpose the correcting source
and he original.

'tiny' beng a somewhat loose term.

You can't do either of the above. Simply because the noise signal is quite
different for every part of those spaces. It is NOT one simple signal, it's
massively complex.

Graham

[Eeyore]

Richard Crowley wrote:

"Greg Locock" wrote ...
Eeyore wrote :
No. It won't work. You can only ever meaningfully cancel
sound over a tiny area (volume).

Such as the entire cabin of a passenger aircraft,

For low frequencies, perhaps. See the other posting on
first-hand experience with active noise cancellation in his
vehicle.

or in some circumstances even a car park or a harbour-
if you can superimpose the correcting source
and he original.

If you can actively counteract the noise at the source (as
an enclosure around a generator, etc.) perhaps. Only a
very limited cases of effective application, at least at this
stage of development.

You can't even do it at the source since it's impossible to precisely co-locate
the 'cancellation signal' with the noise source. never mind issues about
transmission modes etc.

It's easier with lower frequencies of course because the wavelength is longer so
it's more tolerant of the absence of precise co-location. I believe the method's
been used to reduce LF noise in ships' engine rooms. Note *reduce* not
eliminate.

Graham

[Eeyore]

just wondering wrote:

"Knack" wrote in
:

We currently have one of the quietest ceiling fan models in our
bedroom, but I'm wondering if I can suppress that fan noise even
further. However, we don't want to wear earplugs or noise-cancelling
headphones while we sleep.

Just an idea-- Was wondering if it could be possible to somehow make
the sensor and signal processor of one of those noise-canceling
headphones (For example, Panasonic RP-HC500) drive a larger amplifier,
which would in turn power a pair of small cheap PC type speakers. The
little speakers could then be spaced apart above the headboard of our
bed.

Was hoping that I could obtain all components that I need (except the
RP-HC500 and the PC speakers) at Radio Shack or some other local
electronics components retailer. However, I'm not an electronics
tinkerer so I have no clue as to what the specs would be for those
components.

From school (long ago) I have a vague and very limited knowledge of
electronics (Ohm's law, impedence matching), but know nothing about
amplifiers and next to nothing about filters/tuners.

Don't want to spend more than a total of US$400 on this. Is the idea
feasible? If so, then if someone could give me some tips/steering
about the specifics of what I would need, then I'd be greatly
appreciative.


Just to bring some sanity to the discussion, let me point out that what
can vs can not be done will depend on the characterstic of the fan noise
that you want to cancel. Since you don't give any detials, there really
is no difinitive answer. Perhaps the fan motor is coupling 120Hz to the
ceiling structure and the ceiling is acting as a sound board. If this is
the case, mechanically isolating the fan would help. An alternative to
active noise cancellation would be to reduce the speed of the fan.

Indeed. How about using two fans on half speed ?

Graham

[Greg Locock]

Eeyore wrote in
:



Greg Locock wrote:

Eeyore wrote

No. It won't work. You can only ever meaningfully cancel sound over
a tiny area (volume).

Such as the entire cabin of a passenger aircraft, or in some
circumstances even a car park or a harbour- if you can superimpose
the correcting source and he original.

'tiny' beng a somewhat loose term.

You can't do either of the above. Simply because the noise signal is
quite different for every part of those spaces. It is NOT one simple
signal, it's massively complex.




Since it has been demonstrated, documented, and done, I fail to see your
problem.

One of the very early demonstrations of active noise cancellation used a
single source cancelling a ship's exhaust noise.

I have instaled mics on the outside of a car, and demonstrated
cancellation of exhaust noise. Not a generally useul technique, but it
worked.

Finally, anc was used to cancel prop noise inside an aircraft's cabin.

So, what's your problem?


Cheers

Greg Locock

[Greg Locock]

wrote in
ups.com:

On Sep 15, 6:09 pm, Greg Locock wrote:
Eeyore wrote
:

No. It won't work. You can only ever meaningfully cancel sound over
a tiny area (volume).

Such as the entire cabin of a passenger aircraft, or in
some circumstances even a car park or a harbour-
if you can superimpose the correcting source
and he original.

'tiny' beng a somewhat loose term.

Well, even by your own somewhat extraordinary claim, "tiny"
is, in fact, a pretty well defined term: you defined it:

You state it can be done "if you can superimpose the
correcting source and he [sic] original." Fine. So let's
superimpose the original (4 engines on a 747 along
with the entire outside skin of the plane which is where
most of the in-flight noise due to turbulence comes from.

Tum te tum.


Now, using YOUR proposal, please explain to the gathered
audience how you would "superimpose the correcting
source and the original.) The original noise source is
the size of a 747. According to you, if you can superimpose
a second, out-of-phase 747-sized noise source on the
original you're done. So then only place I can put the
correcting source is NEXT to the 747, say at an average
distance of 100 feet, and place the person awaiting the
sonic remedy exactly in between the two.

And how's that working out for you?

Silly eeyore, I said that in /some circumstances/ if there was one source you
could colocate source and corrector. No thistles for you.


The problem with your rather extraordinary claim is that
in an airplane cabin, there is no single "noise source:"
it's all over the place and highly uncorrelated. I can correct
is over a very small area, to the limits of the wavelength
desired whicyh is defined by the highest frequency I
want to cancel, and that is a VERY precise definition of
"tiny."

Practically speaking we want to produce a noticeable reduction in the noise
level, across a useful volume of space. That can be done in a large arbitrary
volume, using several mics and several sound sources.

If we can go one step further and colocate source and corrector then it can be
done more simply. Alternatively if the corrector can be introduced into the
primary noise path then it is also easier.

This has been demonstrated many times.


Cheers

Greg Locock

[Eeyore]

Greg Locock wrote:

Eeyore wrote
Greg Locock wrote:
Eeyore wrote

No. It won't work. You can only ever meaningfully cancel sound over
a tiny area (volume).

Such as the entire cabin of a passenger aircraft, or in some
circumstances even a car park or a harbour- if you can superimpose
the correcting source and he original.

'tiny' beng a somewhat loose term.

You can't do either of the above. Simply because the noise signal is
quite different for every part of those spaces. It is NOT one simple
signal, it's massively complex.

Since it has been demonstrated, documented, and done, I fail to see your
problem.

Others aside from me have explained why it can't be done from basic principles
of physics. If you have an example please post a link.


One of the very early demonstrations of active noise cancellation used a
single source cancelling a ship's exhaust noise.

A ship's exhaust comes from a near 'single point'. If you can co-locate your
'anti-noise' signal close to that, then I imagine you might do a good job of
that. I expect it's also relatively low frequency. These are all things that
were explained to you.

There are plenty of examples of how it can't be done very effectively in the
cabins of cars and other vehicles (at least for wideband noise).


I have instaled mics on the outside of a car, and demonstrated
cancellation of exhaust noise. Not a generally useul technique, but it
worked.

Low frequency again. That's relatively easy to deal with. That's not the OP's
problem.


Finally, anc was used to cancel prop noise inside an aircraft's cabin.

Cite ?

It may reduce it but not cancel it.

Graham

[Eeyore]

Greg Locock wrote:

Practically speaking we want to produce a noticeable reduction in the noise
level, across a useful volume of space. That can be done in a large arbitrary
volume, using several mics and several sound sources.

If we can go one step further and colocate source and corrector then it can be
done more simply. Alternatively if the corrector can be introduced into the
primary noise path then it is also easier.

This has been demonstrated many times.

AT LOW FREQUENCIES ONLY !

Graham

[[email protected]]

On Sep 16, 2:26 am, Greg Locock wrote:
Now, using YOUR proposal, please explain to the gathered
audience how you would "superimpose the correcting
source and the original.) The original noise source is
the size of a 747. According to you, if you can superimpose
a second, out-of-phase 747-sized noise source on the
original you're done. So then only place I can put the
correcting source is NEXT to the 747, say at an average
distance of 100 feet, and place the person awaiting the
sonic remedy exactly in between the two.

And how's that working out for you?

Silly eeyore, I said that in /some circumstances/ if there
was one source you could colocate source and corrector.

No, you, in fact, said:

"Such as the entire cabin of a passenger aircraft, "

Which cabin of which passenger aircraft has one source?

[mike[_4_]]

"Knack" wrote in message
...
We currently have one of the quietest ceiling fan models in our bedroom,
but
I'm wondering if I can suppress that fan noise even further. However, we
don't want to wear earplugs or noise-cancelling headphones while we sleep.

Just an idea-- Was wondering if it could be possible to somehow make the
sensor and signal processor of one of those noise-canceling headphones
(For
example, Panasonic RP-HC500) drive a larger amplifier, which would in turn
power a pair of small cheap PC type speakers. The little speakers could
then
be spaced apart above the headboard of our bed.

Was hoping that I could obtain all components that I need (except the
RP-HC500 and the PC speakers) at Radio Shack or some other local
electronics
components retailer. However, I'm not an electronics tinkerer so I have no
clue as to what the specs would be for those components.

From school (long ago) I have a vague and very limited knowledge of
electronics (Ohm's law, impedence matching), but know nothing about
amplifiers and next to nothing about filters/tuners.

Don't want to spend more th
an a total of US$400 on this. Is the idea
feasible?

For $400.00 you might think about hiring a girl with a large feather
fan to keep you cool. :-) (ala ancient Egypt)
Mike

[Angelo Campanella[_2_]]

wrote:
Now, using YOUR proposal, please explain to the gathered
audience how you would "superimpose the correcting
source and the original.) The original noise source is
the size of a 747. According to you, if you can superimpose
a second, out-of-phase 747-sized noise source on the
original you're done. So then only place I can put the
correcting source is NEXT to the 747, say at an average
distance of 100 feet, and place the person awaiting the
sonic remedy exactly in between the two.

Using the term "noise source" is not appropriate, as you point out it
is remote and complex.

What is always important (or the only action readily feasible) is that
in present day noise canceling devices, only one error microphone is
applied and it senses only the net noise arriving (from a complex
source) at this single listening position.

Higher order noise canceling systems (Plants?) use a sensor at one or
more of the noise sources to obtain precise frequency and phase
information, and via complex computation derive more accurate noise
cancellation, or can project such cancellation to a position that is
neither at the error microphone nor at the canceling loudspeaker.

Perhaps someone here might care to educate us on these signal
processing algorithms.

Angelo Campanella

[Eeyore]

wrote:

Eeyore wrote:
Knack wrote:

We currently have one of the quietest ceiling fan models in our bedroom, but
I'm wondering if I can suppress that fan noise even further. However, we
don't want to wear earplugs or noise-cancelling headphones while we sleep.

Just an idea-- Was wondering if it could be possible to somehow make the
sensor and signal processor of one of those noise-canceling headphones (For
example, Panasonic RP-HC500) drive a larger amplifier, which would in turn
power a pair of small cheap PC type speakers. The little speakers could then
be spaced apart above the headboard of our bed.

No. It won't work. You can only ever meaningfully cancel sound over a tiny area
(volume).


There is a well established industry of active noise control for
entire aircraft cabins from two seater piston engine jobs all the way
to 747 Jumbos.

Here is one example. Very educational reading if you're interested in
noise reduction.

http://www.ultraquiet.com/

From basic physical principles, such a system can only be really effective at low
fequencies.

Graham

[Kevin McMurtrie]

In article ,
wrote:

On Sat, 15 Sep 2007 22:03:37 +0100, Eeyore
wrote:



Knack wrote:

We currently have one of the quietest ceiling fan models in our bedroom,
but
I'm wondering if I can suppress that fan noise even further. However, we
don't want to wear earplugs or noise-cancelling headphones while we sleep.

Just an idea-- Was wondering if it could be possible to somehow make the
sensor and signal processor of one of those noise-canceling headphones
(For
example, Panasonic RP-HC500) drive a larger amplifier, which would in turn
power a pair of small cheap PC type speakers. The little speakers could
then
be spaced apart above the headboard of our bed.

No. It won't work. You can only ever meaningfully cancel sound over a tiny
area
(volume).

Graham

There is a well established industry of active noise control for
entire aircraft cabins from two seater piston engine jobs all the way
to 747 Jumbos.

Here is one example. Very educational reading if you're interested in
noise reduction.

http://www.ultraquiet.com/

This system uses speakers and servos placed at intervals throughout the
cabin. It's not simple and it's still not for higher frequencies. It's
to reduce low frequency rumble caused by propellers or air turbulence.
It won't eliminate the whirring sounds of a fan. Another version is
installed in the headrest of each seat to create a "localised zone of
quiet". Try the interactive demo.

[Angelo Campanella[_2_]]

Eeyore wrote:

Indeed. How about using two fans on half speed ?

That one works. I have found via RSS tests that a fan at half speed
produces 20 dBA less noise. Two fans will raise that by 3 dBA. Hence the
two halves vs one whole provides a 17 dBA fan noise reduction.

Angelo Campanella

[Angelo Campanella[_2_]]

wrote:
Here is one example. Very educational reading if you're interested in
noise reduction.
http://www.ultraquiet.com/

Apparently, a well-developed company in these arts...

I'm interested in the "active tuned vibration damper". As I noted, I
developed, with the ad of an fellow analyst, the tuned vibration damper.
We found (theoretically) that two or three fequency ranges were needed,
the findamental, 2nd and thord harmonics of the prop blade fundamental,
about 130 Hz. In theory, one set per skin panel was required about the
circumference of the fuselage, and for several panels fore and aft of
the propeller plane. That was 1983-84 (time flies!); one conclusion was
that clock spring steel was best as damper spring material... That work
went from Fairchild to SAAB and now to Ultra, so it seems. The apparent
news is that passive is not good enough , since they speak of "active
tuned dampers", but that could mean just that the weight is slid along
the spring by a servo to find the best noise reduction... one never knows...

Angelo Campanella

[Greg Locock]

wrote in news:1189944817.872694.250160@
22g2000hsm.googlegroups.com:

On Sep 16, 2:26 am, Greg Locock wrote:
Now, using YOUR proposal, please explain to the gathered
audience how you would "superimpose the correcting
source and the original.) The original noise source is
the size of a 747. According to you, if you can superimpose
a second, out-of-phase 747-sized noise source on the
original you're done. So then only place I can put the
correcting source is NEXT to the 747, say at an average
distance of 100 feet, and place the person awaiting the
sonic remedy exactly in between the two.

And how's that working out for you?

Silly eeyore, I said that in /some circumstances/ if there
was one source you could colocate source and corrector.

No, you, in fact, said:

"Such as the entire cabin of a passenger aircraft, "

Which cabin of which passenger aircraft has one source?



The cabin of the passenger aircraft used many error mics and many
cancelling loudspeakers. I very much doubt that I said that it was an
example of a single source, single corrector system. IF I did then I
apologise for misleading you. IF I DID NOT then learn to read.

Cheers

Greg Locock

[Greg Locock]

wrote in news:1189944817.872694.250160@
22g2000hsm.googlegroups.com:


No, you, in fact, said:

"Such as the entire cabin of a passenger aircraft, "

Which cabin of which passenger aircraft has one source?




What I wrote was

"
One of the very early demonstrations of active noise cancellation used a
single source cancelling a ship's exhaust noise.

I have instaled mics on the outside of a car, and demonstrated
cancellation of exhaust noise. Not a generally useul technique, but it
worked.

Finally, anc was used to cancel prop noise inside an aircraft's cabin.

"

That does NOT say that the aircraft cancellation system was single
source.

Cheers

Greg Locock

[Knack]

"just wondering" wrote in message
...
"Knack" wrote in
:

We currently have one of the quietest ceiling fan models in our
bedroom, but I'm wondering if I can suppress that fan noise even
further. However, we don't want to wear earplugs or noise-cancelling
headphones while we sleep.

Just an idea-- Was wondering if it could be possible to somehow make
the sensor and signal processor of one of those noise-canceling
headphones (For example, Panasonic RP-HC500) drive a larger amplifier,
which would in turn power a pair of small cheap PC type speakers. The
little speakers could then be spaced apart above the headboard of our
bed.

Was hoping that I could obtain all components that I need (except the
RP-HC500 and the PC speakers) at Radio Shack or some other local
electronics components retailer. However, I'm not an electronics
tinkerer so I have no clue as to what the specs would be for those
components.

From school (long ago) I have a vague and very limited knowledge of
electronics (Ohm's law, impedence matching), but know nothing about
amplifiers and next to nothing about filters/tuners.

Don't want to spend more than a total of US$400 on this. Is the idea
feasible? If so, then if someone could give me some tips/steering
about the specifics of what I would need, then I'd be greatly
appreciative.



Just to bring some sanity to the discussion, let me point out that what
can vs can not be done will depend on the characterstic of the fan noise
that you want to cancel. Since you don't give any detials, there really
is no difinitive answer. Perhaps the fan motor is coupling 120Hz to the
ceiling structure and the ceiling is acting as a sound board. If this is
the case, mechanically isolating the fan would help. An alternative to
active noise cancellation would be to reduce the speed of the fan.

The ceiling fan is well designed. It has an elegant flexible elastomer mount
within its flush mounting base, which in turn makes contact with the room's
soft, low density ceiling tiles that have excellent vibration absorbing
characteristics of their own. So I'm quite certain that practically none of
what I hear is sounding off the ceiling.

However, I can definitely hear two distinctly different noises coming out of
this ceiling fan: a low rumbling sound and a higher pitched sound.
Presumably, the former is due to air turbulence and the latter is from the
electric motor.

Unfortunately the higher pitch sound component is the more objectionable of
the two that I wish to attenuate. Surely, someone with a flush mounting 52"
(132 cm) ceiling fan of their own, and a microphone, and an oscilloscope
could easily tell me what those two frequencies are. Hopefully the two noise
frequencies are both within the attenuable range for ANC. Since posting this
thread I've learned that active noise control (ANC) produces *good* results
only for frequencies below 300 hz.

A typical bedroom is not a huge space. And remember that the design need
only satisfy a maximum of 2 sleepers who's ears will always be located at
approximately the same places whenever noise control is needed. Although the
location of a double-bed cannot be expected to match one of the ceiling's
centerlines exactly, it will be reasonably close, because there will be
space on each side of the bed for separate access (It's not logical to put
the *length* of a double-bed right up against a wall without providing any
access space there.).

For example, our bedroom measures 10'6" x 12' (3.2 m x 3.7 m) and has a
queen size bed located with its centerline only 14" (36 cm) off the
centerline of the room's longer wall. Consequently in 3D space the distance
to the noise source (ceiling fan) from the center of each sleeper's head is
a difference of only 9%. Each sleeper's head would be equally distant at
about 25" (64 cm) from the proposed noise sensor.

Thus, based on the layout of my own bedroom I'm guessing that the size of a
typical bedroom nor the the slightly asymmetrical locations of 2 sleepers in
it shouldn't present much of a problem.

A major problem with implementing the idea is that there will be no
available electronic schematic diagram for any ANC headphone with which to
build the system around. I just realized that the device would have to be
hacked by someone with considerable electronic experience having data about
various ICs in its circuitry. If ICs for the device's signal processor
output and its amplifier input are both proprietary, then I guess I'm stuck.

[Peter Larsen]

Knack wrote:

However, I can definitely hear two distinctly different noises
coming out of this ceiling fan: a low rumbling sound and a higher
pitched sound. Presumably, the former is due to air turbulence
and the latter is from the electric motor.

Appears reasonable.

Unfortunately the higher pitch sound component is the more
objectionable of the two that I wish to attenuate.

Appears reasonable.

Surely, someone with a flush mounting 52" (132 cm) ceiling fan
of their own,

Not just A fan, same make model and possibly batch.

and a microphone, and an oscilloscope

No, a microphone and a computer with a sound application that can do
freuquency content analysis, just one example: a demo of audition will
do nicely.

A typical bedroom is not a huge space. And remember that the
design need only satisfy a maximum of 2 sleepers who's ears
will always be located at approximately the same places whenever
noise control is needed.

ANR's possibiblities are defined by the likelihood of a phase-match, ie.
by the wavelength. It seems probable that the high pitched noise is
caused by some sort of gears or bearings. My guess is that it is in the
kHz range, just a guess and I could be wrong, but I have seen high
pitched noise from powerdrills appear in the 10 kHz band of octave
analysis.

A major problem with implementing the idea is .... that there
will be no available electronic schematic diagram for any ANC
headphone with which to build the system around.

Attenuating high pitched noise at the source is relatively simple, but
there may be cooling necessities that prevent so doing without voiding
the fire safety of the fan.

Stop looking for a complex solution, look for a simple one.


Kind regards

Peter Larsen

[Eeyore]

Knack wrote:

A major problem with implementing the idea is that there will be no
available electronic schematic diagram for any ANC headphone with which to
build the system around. I just realized that the device would have to be
hacked by someone with considerable electronic experience having data about
various ICs in its circuitry. If ICs for the device's signal processor
output and its amplifier input are both proprietary, then I guess I'm stuck.

That's the EASY part !

The major problem would be writing the software.

Graham

[Arny Krueger]

"Peter Larsen" wrote in
message
Knack wrote:

However, I can definitely hear two distinctly different
noises coming out of this ceiling fan: a low rumbling
sound and a higher pitched sound. Presumably, the former
is due to air turbulence and the latter is from the
electric motor.

Appears reasonable.

Unfortunately the higher pitch sound component is the
more objectionable of the two that I wish to attenuate.

Appears reasonable.

At this point another course of action presents itself - change the fan. The
whine (and even the rumble) might be sample defects, or tjey might be due to
a too-cheap design. I've got a number of fans in my house, and there seems
to be a loose correlation between price and SPL. ;-)

Another option which might become more feasible as the calendar moves
towards winter in the Northern Hemisphere, is simply turning the fan off
during critical recording sessions.

[Knack]

"Eeyore" wrote in message
...


Knack wrote:

A major problem with implementing the idea is that there will be no
available electronic schematic diagram for any ANC headphone with which
to
build the system around. I just realized that the device would have to be
hacked by someone with considerable electronic experience having data
about
various ICs in its circuitry. If ICs for the device's signal processor
output and its amplifier input are both proprietary, then I guess I'm
stuck.

That's the EASY part !

The major problem would be writing the software.

Graham

Shouldn't require any new software. The signal processing is all done by the
electronics of the ANC headphone's circuitry. Now must redirect its
anti-noise signal to a larger amplifier than that which drives the
headphone's tiny speakers. All I want to do is replace the ANC headphone's
amplifier and speakers with much larger components. The magnitude of the
amplified anti-noise need only be enough to reach the ears of a person
located only about 10" (25 cm) from a little PC type speaker. How much
anti-noise is that? It should be equal (and opposite) to the magnitude of
noise that can be heard from the center of a fan located no further than 85"
(216 cm) from a sleeper's ear. Remember that the ceiling fan is already
pretty quiet. I just want to get that noise down even further; so that
anyone can sleep through it.

[Knack]

"Eeyore" wrote in message
...


Knack wrote:

A major problem with implementing the idea is that there will be no
available electronic schematic diagram for any ANC headphone with which
to
build the system around. I just realized that the device would have to be
hacked by someone with considerable electronic experience having data
about
various ICs in its circuitry. If ICs for the device's signal processor
output and its amplifier input are both proprietary, then I guess I'm
stuck.

That's the EASY part !

The major problem would be writing the software.

Graham

Shouldn't require any new software. The signal processing is all done by the
electronics of the ANC headphone's circuitry. Now must redirect its
anti-noise signal to a larger amplifier than that which drives the
headphone's tiny speakers. All I want to do is replace the ANC headphone's
amplifier and speakers with much larger components. The magnitude of the
amplified anti-noise need only be enough to reach the ears of a person
located only about 10" (25 cm) from a little PC type speaker. How much
anti-noise is that? It should be equal (and opposite) to the magnitude of
noise that can be heard from the center of a fan located no further than 85"
(216 cm) from a sleeper's ear. Remember that the ceiling fan is already
pretty quiet. I just want to get that noise down even further; so that
anyone can sleep through it.

[Eeyore]

Knack wrote:

"Eeyore" wrote
Knack wrote:

A major problem with implementing the idea is that there will be no
available electronic schematic diagram for any ANC headphone with which
to build the system around. I just realized that the device would have to
be
hacked by someone with considerable electronic experience having data
about various ICs in its circuitry. If ICs for the device's signal
processor
output and its amplifier input are both proprietary, then I guess I'm
stuck.

That's the EASY part !

The major problem would be writing the software.

Shouldn't require any new software. The signal processing is all done by the
electronics of the ANC headphone's circuitry.

I doubt that the signal processing for headphones will be the same as required
for your application.

Graham

[Peter Larsen[_2_]]

Arny Krueger wrote:

Another option which might become more feasible as the calendar moves
towards winter in the Northern Hemisphere, is simply turning the fan
off during critical recording sessions.

My understanding is that the plan is to use the bedroom for something
called:

"sleep", outdated activity from pre the internet era.


Kind regards

Peter Larsen

[Ilya]

There's an article titled "WHAT'S NEXT; To Quiet a Whirring Computer,
Fight Noise With Noise"
about researchers doing this to try to quiet a computer case fan he
http://query.nytimes.com/gst/fullpag...gewanted=print

So, it definitely seems doable, but not as easy as one would think.
However, I don't see any harm in actually trying to build the said
noise canceller,
even if it probably won't work. In the worst case, a few hundred
dollars
will be wasted on a good cause, and this question will be really
answered.

Building it should actually be quite trivial. All you have to do is
replace
the headphones with a pair of computer speakers that have an internal
amplifier (since they take what is essentially a headphone output
anyway).
This might take a bit of soldering, but shouldn't be a big deal.

Then, you could experiment with microphone and speaker placement
and see if it works. Most likely, if it will work, it will only work
with the
microphone and speaker close to the sound source (the fan), but it
might work if you put the speakers and microphone on your bed stand.

If you are interested, you could figure out what frequencies of noise
the
fan is putting out by recording the noise with a mic and then doing an
FFT/frequency analysis using some decent audio processing software
such as Cool Edit.

I do agree that the best remedy though would be to try to eliminate
the source of the noise. A better designed fan could have much lower
motor noise, and the noise due to air motion could be better too if
the fan blades have a better design. If you are using a separate speed
controller for the fan, that could also be causing noise if it is
creating
harmonics in the AC current going to the fan. A better speed
controller
could help in that case.

-Ilya

[Brian Marston]

Knack wrote:
We currently have one of the quietest ceiling fan models in our bedroom, but
I'm wondering if I can suppress that fan noise even further. However, we
don't want to wear earplugs or noise-cancelling headphones while we sleep.

Just an idea-- Was wondering if it could be possible to somehow make the
sensor and signal processor of one of those noise-canceling headphones (For
example, Panasonic RP-HC500) drive a larger amplifier, which would in turn
power a pair of small cheap PC type speakers. The little speakers could then
be spaced apart above the headboard of our bed.

Was hoping that I could obtain all components that I need (except the
RP-HC500 and the PC speakers) at Radio Shack or some other local electronics
components retailer. However, I'm not an electronics tinkerer so I have no
clue as to what the specs would be for those components.

From school (long ago) I have a vague and very limited knowledge of
electronics (Ohm's law, impedence matching), but know nothing about
amplifiers and next to nothing about filters/tuners.

Don't want to spend more than a total of US$400 on this. Is the idea
feasible? If so, then if someone could give me some tips/steering about the
specifics of what I would need, then I'd be greatly appreciative.




Have followed this thread with some amusement.

There is research (still underway) to reproduce realistic 3-D sound
fields for theatrical spaces that may one day feed back into noise
cancellation. Without the resources of a major university and computing
power to suit it is unlikely that to be useful will emerge for several
more years.

Resiliently mounted fan and soft ceiling materials, this in a bedroom
seems to be heading towards a TOO QUIET noise environment, a situation
occasionally encountered, where noise exclusion has gone TOO FAR.

Now may be the time to do some "acoustic back fill" with a white noise
generator to mask the fan and to stop the search for your domestic "cone
of silence".

[Knack]

"Ilya" wrote in message
ups.com...
There's an article titled "WHAT'S NEXT; To Quiet a Whirring Computer,
Fight Noise With Noise"
about researchers doing this to try to quiet a computer case fan he
http://query.nytimes.com/gst/fullpag...gewanted=print

So, it definitely seems doable, but not as easy as one would think.
However, I don't see any harm in actually trying to build the said
noise canceller,
even if it probably won't work. In the worst case, a few hundred
dollars
will be wasted on a good cause, and this question will be really
answered.

Building it should actually be quite trivial. All you have to do is
replace
the headphones with a pair of computer speakers that have an internal
amplifier (since they take what is essentially a headphone output
anyway).
This might take a bit of soldering, but shouldn't be a big deal.

Then, you could experiment with microphone and speaker placement
and see if it works. Most likely, if it will work, it will only work
with the
microphone and speaker close to the sound source (the fan), but it
might work if you put the speakers and microphone on your bed stand.

If you are interested, you could figure out what frequencies of noise
the
fan is putting out by recording the noise with a mic and then doing an
FFT/frequency analysis using some decent audio processing software
such as Cool Edit.

I do agree that the best remedy though would be to try to eliminate
the source of the noise. A better designed fan could have much lower
motor noise, and the noise due to air motion could be better too if
the fan blades have a better design. If you are using a separate speed
controller for the fan, that could also be causing noise if it is
creating
harmonics in the AC current going to the fan. A better speed
controller
could help in that case.

-Ilya

Thank-you! You and I are of the same practical-minded orientation, Ilya. I
agree with the approach that you described. A headphone contains a pair of
earphones, and an earphone's input is close to that of an amplifier's input.
In fact, using a simple adapter cable from Radio Shack I connected my iPod
Nano to my home audio system's amplifier. So yes, all that is required would
be some soldering of the headphone's tiny speaker outputs to an additional
cable that is coupled to the PC speaker's signal cable.

Consumer grade ceiling fans (CFs) typically contain only simple paddles (not
air foils) on their rotors. However there is at least one model, by Sycamore
Technology that does in fact utilizes a quiet air foil as a blade.
http://www.sycamorefan.com/fan/feature/features.html

Moreover, there are commercial / industrial CF models having quiet,
efficient air foil type type blades. Some are made by Big Ass Fans
http://bigassfans.com/pdf/BAF_Powerfoil_Intl.pdf

But I now have 3 bedrooms each containing CFs of conventionally simple
design, which (until earlier today) I was trying to do something about. My
idea was to place the two PC speakers in the shelving built into the bed's
headboard. That way the two sleepers would each get a little speaker located
no further than 10" (25 cm) from their ears. If the noise cancelling
headphone contains but a single sensor (essentially a tiny microphone) then
it was to go in a location midway between the two PC speakers. Or, if the
headphone contained a pair of sensors, then so much the better, as each PC
speaker could gets its own local sensor; not that difficult to split a
headphone in half.

Unfortunately I just made some new observations, and explanations for them
don't indicate that my idea will ever work satisfactorily; maybe for snorers
perhaps, but not CFs ;-)

Yesterday I installed yet another CF of identicle model to the others that
had already been installed prior to my original post. Immediately I noticed
that it was quieter than the others; had less of that high pitched component
of noise, which I described earlier. It then ocurred to me that our other
CFs (now several weeks old) sounded just as good as this one when they were
first installed. Gradually they other must've gotten louder at the higher
frequencies, but I never noticed that change until the new CF was installed
yesterday.

Earlier someone replied that ball bearings were probably the source of the
higher frequencies. Based on my own experience, evidently that's true. When
they're unused, a fan motor's ball bearing units probably have just the
right amount of lubricant in them (for quietest operation), and then after
several weeks of use their lubrication diminishes to some stable level,
which unfortunately results in greater high frequency noise volume.

Today I obtained a Maxell NC-II noise cancelling headphone. The manufacturer
makes a vague and exagerrated claim that the device reduces audible noise up
to 95%, which significantly exceeds claims made by other manufacturers of
far more expensive models. I tested it in two nearly identicle size
bedrooms; one having the newest fan, the other having a several week old
fan. As I had doubted, the device was not able to attenuate any bit of the
ball bearing component of noise. However, it was remarkably effective at
reducing the noise due to rushing air streams. I estimate that when the
device was switched ON, about 2/3 of the air noise was cancelled out. The
residual air noise was noticably higher in pitch than the uncancelled (OFF)
air noise. These results are not encouraging enough for me to pursue the
idea any further with respect to CFs.

[Knack]

"Brian Marston" wrote in message
.. .
Knack wrote:
We currently have one of the quietest ceiling fan models in our bedroom,
but
I'm wondering if I can suppress that fan noise even further. However, we
don't want to wear earplugs or noise-cancelling headphones while we
sleep.

Just an idea-- Was wondering if it could be possible to somehow make the
sensor and signal processor of one of those noise-canceling headphones
(For
example, Panasonic RP-HC500) drive a larger amplifier, which would in
turn
power a pair of small cheap PC type speakers. The little speakers could
then
be spaced apart above the headboard of our bed.

Was hoping that I could obtain all components that I need (except the
RP-HC500 and the PC speakers) at Radio Shack or some other local
electronics
components retailer. However, I'm not an electronics tinkerer so I have
no
clue as to what the specs would be for those components.

From school (long ago) I have a vague and very limited knowledge of
electronics (Ohm's law, impedence matching), but know nothing about
amplifiers and next to nothing about filters/tuners.

Don't want to spend more than a total of US$400 on this. Is the idea
feasible? If so, then if someone could give me some tips/steering about
the
specifics of what I would need, then I'd be greatly appreciative.




Have followed this thread with some amusement.

There is research (still underway) to reproduce realistic 3-D sound fields
for theatrical spaces that may one day feed back into noise cancellation.
Without the resources of a major university and computing power to suit it
is unlikely that to be useful will emerge for several more years.

Resiliently mounted fan and soft ceiling materials, this in a bedroom
seems to be heading towards a TOO QUIET noise environment, a situation
occasionally encountered, where noise exclusion has gone TOO FAR.

Now may be the time to do some "acoustic back fill" with a white noise
generator to mask the fan and to stop the search for your domestic "cone
of silence".

Been long aware of the marketing claim that white noise induces sleep. In
fact, I have first-hand experience testing that claim.

I'll never forget a 2-week canyon river rafting trip. We camped each night
at about a stone throwing distance from the shoreline. Although the
background sound of rushing water (just a minor riffle) was only a low
volume that could easily be ignored during daytime, after about a week that
same sound became maddening at night when we tried to sleep through it.
After a while we all had morning headaches.

And years ago at my ski club's lodge someone in the bedroom turned on a
white noise contraption without bothering to ask if it was OK with the other
overnight guests. Well, after about 20 minutes of sleeplessness (following
our 5-hour drive that night to get to the lodge) we finally had enough of
the infernal thing, and so without bothering to ask its owner, we pulled its
plug ;-)

Marketing depts like to put to practice the old saying "Repeat something
often enough and people start to believe it." ;-)

[Knack]

"Brian Marston" wrote in message
.. .
Knack wrote:
We currently have one of the quietest ceiling fan models in our bedroom,
but
I'm wondering if I can suppress that fan noise even further. However, we
don't want to wear earplugs or noise-cancelling headphones while we
sleep.

Just an idea-- Was wondering if it could be possible to somehow make the
sensor and signal processor of one of those noise-canceling headphones
(For
example, Panasonic RP-HC500) drive a larger amplifier, which would in
turn
power a pair of small cheap PC type speakers. The little speakers could
then
be spaced apart above the headboard of our bed.

Was hoping that I could obtain all components that I need (except the
RP-HC500 and the PC speakers) at Radio Shack or some other local
electronics
components retailer. However, I'm not an electronics tinkerer so I have
no
clue as to what the specs would be for those components.

From school (long ago) I have a vague and very limited knowledge of
electronics (Ohm's law, impedence matching), but know nothing about
amplifiers and next to nothing about filters/tuners.

Don't want to spend more than a total of US$400 on this. Is the idea
feasible? If so, then if someone could give me some tips/steering about
the
specifics of what I would need, then I'd be greatly appreciative.




Have followed this thread with some amusement.

There is research (still underway) to reproduce realistic 3-D sound fields
for theatrical spaces that may one day feed back into noise cancellation.
Without the resources of a major university and computing power to suit it
is unlikely that to be useful will emerge for several more years.

Resiliently mounted fan and soft ceiling materials, this in a bedroom
seems to be heading towards a TOO QUIET noise environment, a situation
occasionally encountered, where noise exclusion has gone TOO FAR.

Now may be the time to do some "acoustic back fill" with a white noise
generator to mask the fan and to stop the search for your domestic "cone
of silence".

Been long aware of the marketing claim that white noise induces sleep. In
fact, I have first-hand experience testing that claim.

I'll never forget a 2-week canyon river rafting trip. We camped each night
at about a stone throwing distance from the shoreline. Although the
background sound of rushing water (just a minor riffle) was only a low
volume that could easily be ignored during daytime, after about a week that
same sound became maddening at night when we tried to sleep through it.
After a while we all had morning headaches.

And years ago at my ski club's lodge someone in the bedroom turned on a
white noise contraption without bothering to ask if it was OK with the other
overnight guests. Well, after about 20 minutes of sleeplessness (following
our 5-hour drive that night to get to the lodge) we finally had enough of
the infernal thing, and so without bothering to ask its owner, we pulled its
plug ;-)

Marketing depts like to put to practice the old saying "Repeat something
often enough and people start to believe it." ;-)

[Brian Marston]

Knack wrote:
"Brian Marston" wrote in message
.. .

Now may be the time to do some "acoustic back fill" with a white noise
generator to mask the fan and to stop the search for your domestic "cone
of silence".

Been long aware of the marketing claim that white noise induces sleep. In
fact, I have first-hand experience testing that claim.

SNIP

And years ago at my ski club's lodge someone in the bedroom turned on a
white noise contraption without bothering to ask if it was OK with the other
overnight guests. Well, after about 20 minutes of sleeplessness (following
our 5-hour drive that night to get to the lodge) we finally had enough of
the infernal thing, and so without bothering to ask its owner, we pulled its
plug ;-)

Marketing depts like to put to practice the old saying "Repeat something
often enough and people start to believe it." ;-)


Some of the hardest problems to deal with have been persons, who have
chased absolute silence so far, that finally they lay awake at night
listening to mysterious "wooshing" noises and an unending
"thud-thud-thud" - demanding it be removed. Only the Grim Reaper could
remove that final "woosh" of breath and "thud-thud-thud" of the heart
beating.

A colleague once advised a client to "Grow up - and open his double
glazed windows - and let the world back in". Having moved to a new home,
he'd sound-proofed everything, and had never actually listened to his
new very quiet surroundings.

Background noise generators can work BUT can take a week or more to
acclimatize to, with the volume increased each night in very small
increments over 2-3 weeks.

White-noise generators are a final resort when nothing else will work,
best delivered to the sufferer via headphones, lest fellow sleepers (?)
contemplate murder.

[Tony[_3_]]

Brian Marston wrote:
Background noise generators can work BUT can take a week or more to
acclimatize to, with the volume increased each night in very small
increments over 2-3 weeks.

I wonder whether people are really referring to white noise, or just using
the term to mean a continuous unidentifiable noise. The point of continuous
noise is to mask intermittent, rhythmic or tonal noise which is more
disturbing to sleep. (That is the theory, and it works for me anyway.) To
do this at all effectively, the masking noise must have energy in the
frequency region close to the frequencies contained in the interfering
noise. If it also has energy in other frequency ranges, it will be louder
than is necessary for effective masking and so more likely to disturb sleep
on its own account. White noise has a lot of high frequency energy, while
most common interfering sounds do not (car alarms and burglar alarms
excepted).
I would start off by measuring the maximum level of the interfering noise,
preferably in 1/3 octave bands but at least in octave bands, and then
tailoring the noise spectrum and level to that.
I've never heard that any sort of noise, as such, is conducive to sleep.
Maybe adverts try to imply it but if they actually say it, it would be
misleading. In all my experience, the quieter the better, down to a very
low level indeed. But then of course minor noises might wake you up. That
might even be useful - I was once woken by an extremely quiet burglar. I
would never have heard him, but it was a very still night in a place far
from traffic and industry.
--
Tony W
My e-mail address has no hyphen
- but please don't use it, reply to the group.

[Brian Marston]

Tony wrote:
Brian Marston wrote:

Background noise generators can work BUT can take a week or more to
acclimatize to, with the volume increased each night in very small
increments over 2-3 weeks.

I wonder whether people are really referring to white noise, or just using
the term to mean a continuous unidentifiable noise. The point of continuous
noise is to mask intermittent, rhythmic or tonal noise which is more
disturbing to sleep. (That is the theory, and it works for me anyway.)
SNIP
I would start off by measuring the maximum level of the interfering noise,
preferably in 1/3 octave bands but at least in octave bands, and then
tailoring the noise spectrum and level to that.

Agreed - I would only recommend masking noise where alternate solutions
would vastly exceed the client's budget and an external sources is
beyond control - a solution of 'last resort'.

I've never heard that any sort of noise, as such, is conducive to sleep.
Maybe adverts try to imply it but if they actually say it, it would be
misleading. In all my experience, the quieter the better, down to a very
low level indeed. But then of course minor noises might wake you up. That
might even be useful - I was once woken by an extremely quiet burglar. I
would never have heard him, but it was a very still night in a place far
from traffic and industry.

I would bottom out noise control at 20-25dB(A) with masking noise only
up to 35dB(A) maximum. Masking can either be a neutral bland noise or
recordings of a collection of familiar 'safe' sounds. It's the client
who wants almost anechoic conditions that worry me.

[David Combs]

In article ,
Knack wrote:


Been long aware of the marketing claim that white noise induces sleep. In
fact, I have first-hand experience testing that claim.

I'll never forget a 2-week canyon river rafting trip. We camped each night
at about a stone throwing distance from the shoreline. Although the
background sound of rushing water (just a minor riffle) was only a low
volume that could easily be ignored during daytime, after about a week that
same sound became maddening at night when we tried to sleep through it.
After a while we all had morning headaches.

And years ago at my ski club's lodge someone in the bedroom turned on a
white noise contraption without bothering to ask if it was OK with the other
overnight guests. Well, after about 20 minutes of sleeplessness (following
our 5-hour drive that night to get to the lodge) we finally had enough of
the infernal thing, and so without bothering to ask its owner, we pulled its
plug ;-)

Marketing depts like to put to practice the old saying "Repeat something
often enough and people start to believe it." ;-)



Yeah, but it does work me. Covers up other sounds (voices, etc) that
*would* keep me awake.

Now, the *kind* of sound-generator is *mechanical*, not electronic
(which few I've listened to I don't like at all), is from
Hammacher Schemecher or however you spell it, got it 20 years
or more ago.

Is a small dome-looking thing, maybe 4inches both high and diameter,
with "fan" kind of thing inside generating (I guess) turbulent
air that hits wee holes to the outside, and that interaction
generates the high frequencies -- probably tons of harmonics
*way* up.

That scheme, in my opinion, *wipes* any (inexpensive) electronic
product on the market (as of 15 yrs ago?).


David