Friday, July 10, 2020
The opposite of 'patient machines'
Headline at Eurekalert:
Engineering: Reducing noise transmitted through an open window
Hmm. Could be interesting. Let's read it.
The goal is admirable:
The authors hope that it could be used to reduce noise levels entering through an open window, while keeping homes ventilated, and could improve the health of people living in cities.Especially important now that we've temporarily and fakely REdiscovered the previously well-known value of fresh air. We won't remember the REdiscovery because we don't learn anything, but the fact remains whether we remember it or not. How do they propose to achieve the goal?
The device, assembled by Bhan Lam and colleagues, consists of 24 loudspeakers (each 4.5 cm in diameter), fixed in a grid pattern to bars attached to the inside of a window and one sensor located outside the window. If the sensor detects noise outside the building, the loudspeakers emit "anti-noise" at the same frequency as the detected noise but with inverted sound waves. This "anti-noise" cancels out the detected noise and reduces the volume of noise pollution entering the room, even when the window is open.And how much benefit do you get from this massive and wildly expensive and energy-consuming megasystem?
The authors observed up to a 10 decibel noise reduction for sounds with a frequency above 300Hz, such as traffic and train noises.10 dB isn't much. It's a barely noticeable difference in most situations. More importantly, perceptual noise reduction is only partly correlated with measured dB. Annoyance comes from several interweaving factors: The meaning of the noise (talk vs buzz, doorknock vs heating duct thump); sudden explosive sounds vs constant rumbles; and the predictability or periodicity of the pattern when not constant. A simple reduction in level for a specified frequency range can be achieved MUCH more cheaply and 'patiently' by redesigning the screen or adding louvered shutters. Some inconclusive musings on the subject. = = = = = Next day: I ran a real test of my musings and got a surprise!
Labels: Patient things
¶ 12:31 AM
