There are plenty of speakers that promise a big sound from a compact package but fail to deliver. The problem is one of physics, but a new device could finally see compact speakers living up to such promises thanks to some clever math and a maze of passive resonant chambers that massively boost the bass that can be produced by a tiny smartphone speaker. Playing a sound through this 3D-printed ABS plastic enclosure is claimed to boost sound pressure levels up to 200 times.
As music technology has developed over the last 30 or so years, there has been a war between convenience and sound quality. The warm sound of vinyl lost out pretty quickly to the portability of cassette tapes. These were then usurped by CDs, which offered a digital version of high fidelity, so quality took the front seat again.
But since MP3s and streaming media stormed the market, the vast majority of music is consumed in compressed formats, and a lot of it is being played on small, convenient devices like phones. Their miniature speakers offer a sound that's awful to an audiophile's ear, but enough for a lot of people.
Portable Bluetooth speakers go some way towards giving a fuller sound, but the problem is physics: you can't create true, immersive bass that can carry across distances without shaking a big ol' speaker membrane to do it. You need to move bulk air. Hence why a tuba needs to be bigger than a trumpet, and why your next door neighbour needs sick 15-inch woofers in his Subaru to shake lattes off saucers when he drives down the local strip.
But a new discovery from a post-doc student at Saudi Arabia's King Abdullah University of Science and Technology (KAUST) threatens to turn this well-established idea on its head.
Working with Likun Zhang at the University of Mississippi, KAUST's Jiajun Zhao and Ying Wu have developed an acoustic resonance device just 10 cm (3.9 in) in diameter, 3D-printed in ABS plastic, that can take the tiny sound source of a smartphone speaker and multiply its sound power 200 times, delivering a bigger, warmer bass sound than you'd expect from a device so small.
The design uses an enclosed space with a series of coiled channels radiating out from the central speaker point. This design slows down the sound – at least, in the outward radiant direction – and allows low-frequency resonances to develop despite the fact that the device itself has a small diameter.
"Through the resonance of the air inside the channels," explains Wu, "a lot more of the electric power of the source is converted to sound power than would otherwise be the case."
What's more, the team found that the sound it generated moved outwards in all directions equally, so it's not a highly directional sound source.
You might have noticed you can get a bigger sound from your phone speaker by sticking your device at the mouth of an empty coffee cup – that's because the entire cup becomes a resonant chamber, something like a speaker cabinet. But this device seems to be able to deliver a larger bass response across a wider range of frequencies, using a series of much smaller, specially designed spaces.
I'd love to hear it in action, and see a frequency response curve for it. Does it emphasize certain wavelengths corresponding to the lengths of those channels as they radiate out? Would it work at a smaller scale, to eventually become something that could be built into a mobile phone design?
Is a 200-times sound pressure multiplication really all that much? After all, the decibel scale is logarithmic, so a 200x boost in sound pressure would represent a little more than 20 decibels. That's about eight clicks on an iPhone volume slider, so it's certainly a nice little boost.
If it doesn't mess the sound up completely by emphasizing certain wavelengths over others, it looks like the kind of thing that could immediately make portable Bluetooth speakers smaller, bassier, lighter, cheaper and more energy efficient. And that would be a step forward in convenience and sound quality, for those who still care about such things.
Where to from here? With no apparent commercial development plans in progress, Jiajun Zhao, the guy in charge of the project, is heading off to Houston, where he plans to work in the energy industry. We hope that's not the last we hear of this design.
The team's paper detailing the device is published in The Journal of the Acoustical Society of America.
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