Hyping Active Noise Reduction

lynlynch,

Perhaps you could cast light on this (No Pun Intended).

In the mid 60's a friend and I happened to be cruising past a small local airport at night when we saw an intense searchlight beam scanning the ground from what appeared to be a helicopter (we could see the cockpit lights).

The strange thing was, there was no sound, not even the ambient noise from insects on a summer night, nothing.

Was this technology available back then?

Not that I am aware of. But I was in high school in the mid 60's.

Electronics had not advanced to the point that you could process information fast enough to produce the canceling wave energy in time to cancel the noise at the source.

High speed digital signal processors weren't around then and they gave us the speed needed to cancel the sound in the 80's.

I drove a Ford Taurus with an electronic muffler for 6 months as my personal "test" car. Straight through exhaust with a rugged speaker box at the exhaust outlet. It had a dash switch that allowed me to turn the electronics on and off at will.

Imagine the stares I got when playing with that switch in traffic.

BTW, noise cancellation had it roots in England. Some of our intellectual property came from there, as did our acoustics genus, Owen Jones.

It was one of those experiences that you never forget, like an acoustic "blanket".

Strange.

Considering the British roots in microwave technology, It is not surprising the audio spectrum would be involved as well.

Thanks.