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If you are interested in learning more about Active Noise Control you can start with the Active Control of Noise and Vibration books by Hansen and regarding annoyance from increased speech intelligibility, you can find more information in the Effects of Noise Reduction on Speech Intelligibility, Perceived Listening Effort, and Personal ...
$\begingroup$ Try reading about superposition of waves and active noise cancellation. Active noise cancellation is a common technique employed by (relatively) high-end noise cancelling headphones, so technically it qualifies as 'tried and tested', just like conventional passive techniques like sound-absorbing materials. $\endgroup$ –
This seems to be an elusive area of acoustic science. I want to reduce a dance club’s outdoor noise pollution. Has to be movable nightly covering at least up 500 Hz. What I’m trying to find out is what are the physics working against making active noise cancellation work on a neighborly scale.
However it's rarely possible to cancel the sound over more than a very small region. The cancellation requires the amplitude of the cancelling sound to be precisely matched to amplitude of the noise. The trouble is that the amplitude of sound typically decreases as the inverse square of distance from its source.
Therefore, by taking an existing sound wave and producing a second wave which is exactly its inverse, the two will sum up to zero. This is how active noise cancelling headset works - by "listening" to the exterior sound with a microphone, then reverting it in its speaker. The problem is, where does the energy go? The noise sound is an energy ...
Active noise cancelling reduces unwanted sound by sending the inverted phase of the original phase: (Source: Wikipedia) Theoretically, this seems logical to me. However, in real life, the anti-noise must be created by some hardware or software system (like active noise cancelling headphones), which takes time.
There are other points, P, in the room where destructive interference will occur, but only for certain frequencies of sound. If S $_1$ and S $_2$ are the positions of the speakers, and P is on the 'diagonal' line $\text S_1\text S_2$ then for in phase speakers $$|\text S_2 \text P-\text S_1 \text P|=n\lambda $$
We know that active noise cancelling headphones work by playing a signal in your ear which is 180º out of phase with the ambient noise. If we compare the two waves, the peak in one wave is completely inverted as a valley in the other. Together, they cancel each other out and we don't hear anything.
Here is the answer. Background: In the bottom surface of the kettle are many microscopically tiny pores, cracks and crevices. many of these retain extremely minute amounts of air after the kettle is filled with water. these air-charged pores will serve as nucleation sites, at which the boiling process will first be triggered.
Finally, for more information on such calculations, one could look in books such as "Engineering Acoustics - An Introduction to Noise Control" by Michael Mösrer, "Engineering Noise Control" by David Bies et al., the corresponding chapter (chapter 10) from "World Health Organisation's publication" and "Building Acoustics" by Tor Erik Vigran.