Hacker News Reader

Comment by ScottBurson | Hacker News Reader

"Cancel 94%" sounds like a lot, but that's just -12dB — significant, certainly, but nowhere near making audible sounds inaudible.

View on HN

And it's very unlikely to be a broadband attenuator. Attenuating a single frequency is a neat trick, but most acoustic applications require require something that works a wide frequency range.

Given the breathless tone and the curious turns of phrase, I strongly suspect the author has no background in sound, acoustics, science, or journalism.

It could still be very useful without being wide-band!

Particularly with fan noise, there’s often one or two stand-out annoying harmonics while the wide-band noise is less offensive.

The author is probably one of those science journalist that has a at best shaky grasp of the material--these people have to write appealing articles (they're basically advertising the university) for a whole lot of different disciplines, so it's not going to be easy.

And I think the point is that this blocks out only certain frequencies, without being a massive structure (you can easily make a serpentine acoustic notch filter but it's gonna be huge)

And for comparison, a single 4mm pane of glass is about -27db, and cheap commodity wall board is about -46db (https://www.insulationsuperstore.co.uk/product/soundboard-3-...)

For those of you who haven't yet read the article, the cool thing about this new technology is that the material is not a solid plane, but an empty ring that allows air to pass through:

https://www.bu.edu/research/files/2019/02/acoustic-metamater...

So, essentially, they invented a silencer/muffler?

Certainly interesting, but the applications of that would be somewhat niche.

To be specific, there are not that many scenarios where a solid wall won't do, but a honeycomb-like barrier is OK. Aesthetics are important, but musicians in a studio couldn't care less about how stuff looks as long as it works (and so do your musicians' neighbors).

One good application, as others have mentioned, is putting that thing around a fan, to minimize noise (a solid barrier defeats the purpose of a fan). I wonder what else would be a killer feature application of this kind of structure.

I know nothing about acoustics and its units - the abstract of actual paper says more precisely that it reduces the 'acoustic energy' by 94%, not the power. Can you convert this to a decibel figure? Would you mind explaining what these units mean and how you do the conversions?

It’s a logarithmic scale, which is reasonably approximated as an increase of 3 dB doubling the power (“acoustic energy” is synonymous). A 94% reduction means you’ve reduced it to 6% of the original, which is about a 12 dB reduction (you can figure it in your head like so: 3 dB = 50%, 6 dB = 25%, 9 dB = 12.5%, 12 dB = 6.25%).

For more info, see https://simple.wikipedia.org/wiki/Decibel (which is much more approachable than https://en.wikipedia.org/wiki/Decibel).

Reply on news.ycombinator.com