Sound Destroys Sound

[planet10]

kelticwizard asked for more on this topic in another thread. From August 1954 Radio Electronics magazine.

dave

[fdegrove]

Hi,

Isn't the same principle still used to combat earthquakes in Japan?

Cheers,

[Nelson Pass]

The concept was used for the Shadow, marketed by
Threshold under the Phantom Acoustics label.

Worked pretty well, but was poorly understood and
expensive.


pass/ - still got a pair of those.

[macka]

The same principle is used in noise cancelling Safety Ear Muffs to null out constant machine noise, but enable the user to hear some calling for them.

Hey, if your Misses nags repeatedly these would be handy

Ian

[roddyama]

This principle is also heavily researched and implemented in various forms in road noise reduction techniques in the automotive industry.

Rodd Yamashita

[pinkmouse]

It was also the reason behind the NEXT panel speaker, it was developed by the British MOD for noise cancelling in helicopter cockpits.

[fdegrove]

Hi,

It would be interesting to use this to cancel room resonances amongst other things.

Maybe Nelson would be so kind as to shed some light on how Treshold implemented this interesting theory.

Cheers,

[Neutron Bob]

I ran those beasties for a trial run years ago! Nelson's right, they were pretty amazing. Actually on par with the cost of RPG or similar baffling of the listening room. I liked them, and they did look very cool.

It played tricks on the mind to shut them down and note the subtle differences! I think such a device is the ticket for difficult situations.

The Pacific Symphony Orchestra benefitted immensely from this method (active suppression) in the fitting of the OC Performing Arts Center. Before it, I was being bombarded with stray reflections...actually nasty like a pair of those Bose thingies hanging from the ceiling. (I think some die hard fans might get their feathers ruffled at that...but I experimented for weeks with those things. Give me a proper array of speakers any day...like a set of Rushmores to sit with!)

Bob

[kelticwizard]

Originally posted by planet10
kelticwizard asked for more on this topic in another thread. From August 1954 Radio Electronics magazine.

dave

Thank you geatly, Dave. An April Fool's Day joke. Amazing.

[Nelson Pass]

It's worth noting that we are talking about 2 different
approaches. The standard noise cancelling stuff used
in industry and headphones is generally done by digital
circuitry and is used to remove repetitive waves by analyzing
them with DSP and creating their opposites. This doesn't
work with non-repetitive signals. It's great for noise
reduction, but not suitable for music.

The acoustic feedback as described by Olson and used in
the Shadow is direct: microphone to amplifier to speaker,
and works on instantaneous signals. It's great for audio,
but not as effective for noise reduction.

The patent cover page for the Shadow can be seen at the
www.passlabs.com web site. You can get the full text and
drawing version elsewhere.

By the way, it may be that the original concept was from
Arthur C. Clarke, in his story "Silence Please" / Tales from
the White Hart


pass/ - listening to Zappa's "The Orange County Lumber Truck"
of which he has 4 versions.