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Q & A: A shield against sound.

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Most recent answer: 05/09/2017
Q:
Is it possible to have total elimination / conversion / absorption of sound waves without the use of bulky composites, foams and wool material? Like a invisible shield that does not let sound wave enter the protected area.
- Seth (age 28)
Perak, Malaysia
A:

Hi Seth,

We already have invisible sound shields, of sorts. They are already available commercially: noise-cancelling headphones.

The principle is simple: measure the incoming sound wave, and broadcast (using standard speakers) the exact same wave, but out of phase. The waves superpose, or add up, as all waves do; since they are out of phase, they cancel exactly.

However, I'm pretty sure this could only work within a closed space, like headphones or an airplane cockpit.

If you wanted to shield something in free space, I think you'd need some sort of cloak made of bulky composites, as you said (see wikipedia: "soundproofing"). I can't think of anything which isn't somewhat bulky that reflects or absorbs a high percentage of sound.

Cheers,

David Schmid


(published on 06/26/2013)

Follow-Up #1: reducing noise

Q:
Acquaintance of mine living in Mt. Carroll, IL had a building next to his house convert to a tavern with rock band music on Friday and Saturday nights from the second story of this structure with open windows toward his bedroom. Tavern owner will not close the windows nor add insulation to the bare roof structure over the band. Sound levels are over 75 dB at his lot line. How can this noise be limited reasonably? Are you the best to answer this question?
- Jack Thorne (age 86)
Glen Ellyn, IL USA
A:

That does sound like a miserable situation. We probably aren't good people to give advice. Maybe a lawyer would be better.

The people in the house behind ours occasionally get very noisy. A thick stand of tall bamboo helped reduce the sound a bit. That takes a few years to grow, and even then can't be counted on to be thick every year. Maybe another reader will have a good idea.

Mike W.


(published on 05/09/2017)

Follow-up on this answer.