Engineers invent an Acoustic Prism

opticks-prismRead an article in Scientific American online (Engineers Debut the Acoustic Prism article, EPFL [Ecole Politechnique Fe´de´ral de Lausanne] press release, YouTube video) that discussed a newly invented device, the Acoustic Prism. The prism was invented by Hervé Lissek and his team at EPFL

acoustic-prism1An acoustic prism acts on sound waves similar to the way an optical prism acts on light waves by separating out the composite frequencies of the incoming signal into isolated frequencies of an outgoing signal.

The Acoustic prism

Apparently the acoustic prism is made up of metallic cavities (cells) acoustic-prism2separated by a membrane that (delays) sound waves of a certain frequency down a channel in order to isolate the frequencies of the incoming sound.

Not quite sure what the purpose of the membranes are other than to somehow normalize the incoming sound waves so that it seems like it is hitting all the cavities at the same time. And what constitutes the prismatic effect in the above is not

The acoustic prism on display in the YouTube video looks like a long metallic rectangular tube with ten holes along one side and a microphone at one end and the cavities in the middle. The sound enters one end (to the right in the photo below) and it escapes through the holes in the tube, high frequency sounds closer to the acoustic-prism3source and low frequency sounds farther away from the source. The membranes delay the sound propagating down the tube based on frequency which allows that frequency to depart the tube.

So the composite sound is separated out into it’s constituent parts and dispersed out of the tube in individual sound waves, not unlike an optical prism. Why ten holes and not twenty or thirty is one question and it would seem that the membranes would need the be engineered separately for each frequency you want to isolate.

Study of optical prisms changed the world

It seems to me the study of light, coming from optical prisms discussed by Newton in his Opticks in 1704 led the way to the Enlightenment and to ultimately a redefinition of light as we know it today.

As I have both hearing and eyesight difficulties, it has always confounded me that a simple lens like device can correct for just about any and all eye imperfections and allow me to read anything I need to. But nothing similar is available for improving hearing (ear) defects.

We need an Acoustic Lens

If there were some sort of sound lens it could correct incoming sound frequencies automatically to overcome any ear defects. An optical lens works just as well for noisy or non-noisy (light) environments without problem. I suppose it’s because it modifies all incoming  light wavelengths the same way.

I believe electronic comb filters/digital waveguides should have been able to do this with proper processing power, but they seem at best a modest improvement. There just is nothing similar for hearing to what eyeglasses/bifocals can do for eyesight and light waves.

Maybe if there were some sort of acoustic lens that was able to frequency shift across a number of frequencies into other frequencies. If there is such a thing as an acoustic prism that refracts sound waves well then there should certainly be a way to combine these refracting surfaces to shift acoustic frequencies to something that was more effective.

Acoustic lens practicalities

Not sure what’s at the other end of the acoustic prism rectangular tube but you are supposed to be able to speak at one end of it and hear the constituent parts of the sound emerge out of the face with the ten holes.

It’s a bit much to be wearing something like this around an ear today but it’s just a start. And yes, I realize that a prism is not a lens but they both work via refraction. If one can isolate frequencies, one should be able to (electronically or mechanically) convert one to another, and then (electronically or mechanically) combine the ones that matter into some sort of output sound stream.

So we would need to miniaturize it considerably. Also it would be more helpful if it were somehow circular or spiral so it could be worn over an ear not unlike headphones or ear muffs. If necessary, the electronics to process the incoming sound, modify it’s frequencies to whats needed and output them (through some sort of speakers) could be embedded in the headphones. And there you have it.

It would be very nice if someday, it came in a rechargeable Bluetooth earpiece form factor but that could be generation 3 or 4 or …

Anyways, barring some sort of genetic engineering solution that produces a brand new ear cochlea, either in situ or via transplantation, there is nothing other than modest electronic means (today’s hearing aids) available today to solve hearing problems. But the Acoustic Prism is just a start and its applications seem endless.

I look forward to some day in the future where I can wear an EarGlasses to hear better…


Photo credits: Opticks by Sir Isaac. Newton Knt., from Google Books, Screen shots from the Youtube video, discussing the device 

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