Active Noise Reduction Whisper Mode on Apache AH-64 and newer Stealth Choppers!

New Active Noise Reduction Whisper Mode
on Apache AH-64 Longbow rotary aircraft!


====

Active noise cancellation on newer block AH-64 Longbow Attack Helicopters
and the newer, more hidden STEALTH rotary aircraft takes a twist from
Bose Headphone technology and puts into choppers!

Combining V-shaped blade tips with a pronounced S-curve
AND some active 180-degree out-of-phase sound emissions
technology, the newest-block AH-64's and still-secret
Stealthy twin-engine attack choppers can reduce their
noise signature by a whopping 50%+ at distances as
close as even 50 meters (150 feet!).

By physically modelling the pressure waves created
by chopper blades under various engine loads and
air/weather conditions, small-but-very-powerful
transducers can emit the very sound produced
by the chopper blades and local environment but
reshaped 180-degrees out-of-phase thus nearly
cancelling-out the huge noise footprint of
rotary aircraft.

This technology is almost identical to that
used in Bose Noise Cancelling headphones which
record the surrounding environment, twist the
waveform and re-emit it out-of-phase to create
a self-cancelling waveform.

Think of two rocks thrown into a pond
three feet apart of each other where
the oncoming splashes cancel each out
as they meet (technically, they actually
form a standing wave) which reduces
overall waveform signature.

That same Bose technology is now used
in helicopter noise footprint suppression
with the ADDED BONUS that the local sound
environment no longer has to be recorded
during flight but merely have its waveform
signature acoustically pre-modelled and
those vectorized waveforms re-shaped
and re-emitted at runtime by an onboard
DSP chip (Digital Signal Processor)!

This means MANY sound environments from
around the world (i.e. urban or rural)
can be pre-recorded and/or pre-modelled
and burned into memory chips for instantaneous
access and recall based upon local conditions...OR....
an on-boards expert system can "automatically listen"
to the local environment and shape/rephase
the 180-degrees out-of-phase acoustic emissions
to BEST MATCH the current runtime environment.

This means a chopper can go from an
urban environment to a rural one and
still stay "acoustically hidden" from
prying ears as the computer adapts
and mixes audio waveforms to match
local conditions and the pre-modelled
engine/blade noise.

So from 150 feet away, the newest attack
choppers can be 75 db OR LESS in absolute
average loudness. In some cases, the computer
is fast enough and accurate enough to get
noise levels down to less than 60 db !!!!

One person I recently talked to, found
himself with an AH-64 coming slowly
behind him with its nose tilted sharply
down behind him at less than 250 feet away
angling his rotor wash AWAY from the soldier.
The SHOCK in his face was telling as he heard
but only a little fluttering behind him thinking
it was only the local mountain environment!

Imagine THIS technique used to sneak up onto insurgents!

Active Noise Control:
en.wikipedia.org...

Noise Cancelling Headphones:
en.wikipedia.org...


Helicopter Noise Reduction Technology (Sikorsky):
www.icao.int...


Revolutionary Concepts for Helicopter Noise
Reduction — S.I.L.E.N.T. Program:
Bryan Edwards and Charles Cox
Bell Helicopter Textron Inc., Fort Worth, Texas
citeseerx.ist.psu.edu...

Helicopter Noise Reduction By Actively Controlled Flaps
Daniel Patt, Li Liu†, and Peretz P. Friedmann‡
University of Michigan, Ann Arbor, MI 48109-2140 USA
deepblue.lib.umich.edu...


Eurocopter's Blue Edge Blade makes choppers Stealthy!
gizmodo.com...

Variable CHord helicopter blades to reduce noise:
www.google.ch...

Frequency DOmain Active Noise Cancellation System by Vor Data Systems:
www.google.com...

These are some INTERESTING PATENTS and articles on active noise suppression!

So from 1982-area levels of passive/semi-active noise suppression
to fully 2010's era ACTIVE DSP-based noise-suppression is a BIG JUMP
such where people can't hear a chopper hovering even just overhead!

a reply to: StargateSG7

Apaches had whisper mode in 1982.......why this thread? I saw a demo in 1982 at a secret location.
The one i saw, could not be heard until it was less than 200 meters away, and that was in 1982

Another one surprised me while pi**ing in a field in 2013.

Anti-noise is big business now, you can buy little boxes with headphones at airports that drown out the jet noise, right?
So just mount that on a Heli & hey presto, silent chopper LOL
OK so the Apache had a mech advantage to the sound problem.
Only the Sikorsky & Westland choppers, they make so much noise you can hear them from 5k or more and yet they still managed to take Bin Laden by surprise?
Were his guards all drunk or something?

a reply to: playswithmachines

The difference today is HOW CLOSE you can get without being discovered!

Angle your rotor wash AWAY from the front, moving slowly,
flying into the sun and/or wind and your opponents will
NEVER know what hit them. That soldier I talked about
earlier had the chopper as close as 150 feet away with barely
a low flutter sound.. he originally thought it was the wind
and trees before he turned around!

Scared him pantsless!

New systems take advantage of computer-based pre-modelling
of engine/blade noise and rural/urban acoustic environments
which can be reshaped on-the-fly for noise suppression which
is why I listed the idea as something NEW!

That sort of real-time on-board DSP (Digital Signal Processing)
was NOT available in 1982 and only because CHEAP DSP's were able
to be created because of advances in CMOS chip making techniques
and improvements in audio systems made mostly by Bose and Sony
during the 1980's that made it COST-effective to put on helicopters!

a reply to: playswithmachines

Apaches had whisper mode in 1982.......why this thread? I saw a demo in 1982 at a secret location.
The one i saw, could not be heard until it was less than 200 meters away, and that was in 1982

I had a friend back then who observed a night attack demonstration by these silent choppers somewhere in Europe. They were assembled in an area in total darkness, and waited.

Suddenly, flares popped over head lighting up the target and apaches hovering just above the ground opened fire on the target and destroyed it. The lights went out and the helos left, silent as they came.

Edit: This one is pretty quiet considering proximity to the camera. About :30 into here...

THEY had this in the Sanluis valley in the 70s for cattle mutilation missona supposedly..www.ourstrangeplanet.com...

agrokrag.tumblr.com...


I guess Testors was right about those LHX curved blades as well..www.puertoriconet.com...

a reply to: StargateSG7

Then there is always my favorite topic, graphene! ATS link: Nasa Releases Patents to Public.

Nice to actually see progress from the black project world to the gray and public worlds.

originally posted by: cavtrooper7
THEY had this in the Sanluis valley in the 70s for cattle mutilation missona supposedly..www.ourstrangeplanet.com...

I guess Testors was right about those LHX curved blades as well..www.puertoriconet.com...

---

Curved blade designs can even be used on submarine for anti-cavitation purposes:

Russian Kursk Class submarine curved blade propellors:
i65.tinypic.com...

Chinese Song-class curved blades:
i.imgur.com...

To be used eventally on types of stealthy helicopters
such as the RH 77 from Russia. I say ad a five-bladed
V-tipped S-curve blade and that chopper would be
really stealthy!

forum.nationstates.net...

a reply to: StargateSG7

Nationstates is a video game ,maybe a Hokum or a Havok.

Was that article sponsored by Bose by any chance? It's as if only Bose have used active noise cancelling.

Another clever use (some 20 or so years ago) was to cancel out the noise from the massive fans inside cooling towers.A microphone picked up the sound at nearby houses,which was fed back to speakers placed near the towers and played back 180 degrees out of phase.When the two sound waves reached the houses they cancelled each other out and the noise from the big fans was almost inaudible.

originally posted by: cavtrooper7
a reply to: StargateSG7

Nationstates is a video game ,maybe a Hokum or a Havok.

I actually knew that but the ship is a photo
I think from the Indian Airforce as a concept
for a light attack helicopter. Can't really tell
if it's a 3D rendering or not because either
the lighting was done perfectly during render-out
or it's a wooden mockup of a real design which
is what I mostly suspect.

This photo is the actual LAH from India:

Indian Light Combat Helicopter (LCH) which is being developed by Hindustan Aeronautics Limited (HAL)

4.bp.blogspot.com... at+helicopter+army+in+India+by+Hindustan+Aeronautics+Limited+%25282%2529.jpg

That NationStates concept could be a RE-RENDER
of the original Indian Air Foirce concept but I can't
tell because it really IS a well-done 3D render and
composite job if it's all-fake! To me, it looks like
a wooden-mockup done as a movie prop because
of the seams I see which look like paint-overs of
plywood panel edges but that could be a 3D
rendering artifact coming from a low
polygon count too!

Anyways kudos to the 3D compositor if it's fake!
It looks very real to me!

a reply to: Imagewerx

Bose and Sony merely made it CHEAP and PLENTIFUL!

They produced the designs and software for LOW-COST
DSP which allows such noise reduction to take place
in real-time on consumer-level, professional-level
AND military products at a much-reduced price
compared to what it cost in the 1970's/1980's
when the technology first became widespread!

a reply to: StargateSG7

Looks like a Mangusta kind of...
www.army-technology.com...

Ahh reminds me of Airwolf and Blue thunder. Activate whisper mode Dom.

a reply to: StargateSG7

You've got it ALLLLLLLL wrong. Try again.

-local sonics expert

originally posted by: aholic
a reply to: StargateSG7

You've got it ALLLLLLLL wrong. Try again.

-local sonics expert

===

What parts do you have a problem with
the 180 degrees out of phase?

The physical pre-modelling of pressure waves
using MATHEMATICAL MODELLING of pressure
wave propagation and reflection/absorption
by THOUSANDS of common materials and
terrain features and/or object shapes
(i.e. acoustic waves are from 1hz to 100,000 hz)
for reshaping by a DSP? You can use particle physics
engines for this type of acoustic modelling!

You have an issue with the use of ceramic or plate
tranducers for "listening" and emission of a live
reshaped and remixed acoustic environment?

What's all wrong about it?

Hows your sonics? --- Mine seem to be decent enough at only about
25+ Years experience after SAIT CTSR (Cinema, Television, Stage and Radio Arts)
and lots of experience on Sound Forge, Pro-Tools, Neve, SSL Scenaria, yada yada yada
So I am gonna bet that the many times I've mixed some
background noise out-of-phase to bring out some
in-the-wild voices still works these days !!!

Do you have a problem with the waveform
propogation calculations of our engineers
most of whom have 2 PhD's in Physics,
Computer Science and our MSc's in
Materials Sciences and/or Chemistry
and/or Nuclear Systems, and even
our MScEE's that have only designed
some of the Top 10 Audio/Video
DSP and RISC CPU chips in the World?

Which scenarios are SO COMPLETELY WRONG
that I need to get a return response from
our world-class Audio/Video DSP designers
and CMOS process engineers..........????

Please do elucidate....I'm no acoustics expert
but I know live mixing and editing/switching
and it seems that Active Noise Cancellation
SEEMS to reduce the average loudness of
acoustic events by a significant amount.

a reply to: StargateSG7

You seem to be very good at linking to articles that you know nothing about. Not to mention naming companies. We don't use Sony Sound Forge nor Avid Pro Tools in the govt. Sorry.

Phase cancellation doesn't occur in the atmosphere like you are claiming. Can you imagine the type of transducer that would be required to accurately noise-cancel a helicopter blade cycling at 200+mps in a ever-changing acoustic environment like your Bose headphones or BMW? If so, show me where it lives on the the AH-64. Pictures.

You're living in a mixing and editing world and you'e got no experience in aeronautic sonic suppression. Audio engineers are not engineers, I'm sorry.

originally posted by: aholic
a reply to: StargateSG7

You seem to be very good at linking to articles that you know nothing about. Not to mention naming companies. We don't use Sony Sound Forge nor Avid Pro Tools in the govt. Sorry.

Phase cancellation doesn't occur in the atmosphere like you are claiming. Can you imagine the type of transducer that would be required to accurately noise-cancel a helicopter blade cycling at 200+mps in a ever-changing acoustic environment like your Bose headphones or BMW? If so, show me where it lives on the the AH-64. Pictures.

You're living in a mixing and editing world and you'e got no experience in aeronautic sonic suppression. Audio engineers are not engineers, I'm sorry.

---

I'm NOT an audio engineer. I just act like one.

I press some buttons and move some faders very well in time.... :-)

So, of course I don't have pictures of a transducer
on an AH-64 !!! --- I don't fly them, I only regurgitate
what I hear from others AFTER putting my own
biased spin on their words!

The transducer(s) would have to be quite large
and would have to be sub-millisecond responsive
which means some sort of ceramic plate design
peizo-electric probably made of sapphire or other
glass-like substance. In the case of the AH-64,
I would make it a Hemispherical Peizo-electric
Transducer to be put on the front camera assembly.
That looks to be at least 1.5 feet to 2 feet
in diameter and with layered ceramics
I'm guessing it's reponse time could be
into the tens of microseconds range.

Add in nano-second GPU-type processsing speeds,
I think it could be done on a practical basis since
video has a LOT more data than audio even IF local
acoustic environments have to be taken into account
for phase cancellation methods.

I am going to be careful with using the term "Phase cancellation"
because I personally think "Noise Reduction" is a better term since
any signal processing delays EVEN at sub-millisecond response
rates would STILL leave some waveforms not fully cancelled-out
and as you have correctly outlined, the acoustic environment
in the real world is FAR TOO VARIABLE to be accurately modelled
in real-time. It can only be PREDICTED based upon pre-modelled
environments which means noise suppression won't be truly
complete only good enough for MOST purposes.

On a technical note, for the AH-64 most of the noise reduction
actually comes from the V-style tips of the main chopper blades
and from the angular placement of the tail rotor (55 degrees).

And based upon my rather limited understanding of acoustics,
an interference pattern is created when the in-phase and out-of-phase
waveforms collide/meet/mix and basically standing waves occur to limit
perceiveable differences between the strong impulse-based acoustic
events such as the chop-chop sound of helicopter blades.

Now for the acoustic modelling stuff, I would leave that
to the TRUE engineers who helped develop the DSP chips
that go into real-world audio/video systems .....and wait
for it....BOSE noise cancellation headphones.... :-)

a reply to: aholic

What does the government use for audio/video production then
...Audacity and MovieMaker? (actually those are PRETTY GOOD PROGRAMS --- I USE'EM TOO!)

Just curious as to what you actually use.


----


And since acosutic waveforms ARE EM (1 HZ to 100,000 HZ)
you CAN mathematically model reflection, multi-path, interference,
absorption, refraction, diffraction as you would optical waveforms
and MODEL waveform behaviour to quite a significant and predictable level!
Our engineers use particle physics and optical systems software to do exactly
that for acoustic waveforms!

originally posted by: aholic
a reply to: StargateSG7

You seem to be very good at linking to articles that you know nothing about. Not to mention naming companies. We don't use Sony Sound Forge nor Avid Pro Tools in the govt. Sorry.

Phase cancellation doesn't occur in the atmosphere like you are claiming. Can you imagine the type of transducer that would be required to accurately noise-cancel a helicopter blade cycling at 200+mps in a ever-changing acoustic environment like your Bose headphones or BMW? If so, show me where it lives on the the AH-64. Pictures.

You're living in a mixing and editing world and you'e got no experience in aeronautic sonic suppression. Audio engineers are not engineers, I'm sorry.

Probably true dat.....however posting to say that someone elses info is wrong, whilst implying you are some sort of ITK- without providing one iota of useful information or proof yourself (again!)...is equally as misguided.

Yes i'm well aware of the state of electronics in '82, and would think that the silent mode was mostly shaped blades, rear pitch etc, but then the electronics we see & what the military have, are worlds apart. The early processors were developed for guiding early ICBM's and it's amazing what you can do with just 256Kb of code.

I recently got me some mil-spec SMD chips, which can be used in space, one day soon i hope to get round to testing them in that environment

The cockpit door on the Cocorde was bulletproof, they were obviously thinking ahead....