Metamaterials for acoustic absorption/diffusion

[ripmixburn]

As an owner of the original KEF LS50, I was green to envy to to see them introduce the LS50 Meta containing an interesting man-made material that absorbed problematic interactions between the driver and the cabinet. The original LS50 measured poorly here, but the Meta fared far better. So if that was one of the changes, there is clearly something to the metamaterial and they are surprisingly not mentioned often on Audio Science Review. It's audio science!

While I was down the rabbit hole looking for solutions to my acoustically challenging attic I came across this DIY project for a metamaterial enclosure.

Further down the hole I came across this discussion of Acoustic Metamaterials with Steve Cummer, professor of electrical and computer engineering at Duke University.

Nissan demo

After seeing this demonstration, it correct to assume that the bulky acoustic treatment market is about to be revolutionized?

 

[stevenswall]

After seeing this demonstration, it correct to assume that the bulky acoustic treatment market is about to be revolutionized?

I don't think so, because most of these have never been brought to market in a consumer friendly way, and the ones that have been brought to the market are part of another product and I'm not sure a company that sells acoustic treatment has the means or the will to start fabricating this stuff.

Years before the LS50 Meta several acoustic metamaterials were shown in a few whitepapers... They just aren't available for people to purchase and seem to be stuck in the 'cool things researchers and engineers made but you can't actually get.'

 

[Lambda]

There are hard limits for how small and effective you can make something in relation to the wavelength.
Sure you can engineer materials to do multiple jobs like Dispersion/diffusion absorption and blocking of transmission at the same time.
Save some space and wight.

For room acoustic treatment More is often better and more is limited by cost.
So making it cheap is driving factor.

For low frequency, active cancellation is maybe the better approach.

 

[stevenswall]

For room acoustic treatment More is often better and more is limited by cost.
So making it cheap is driving factor.

For low frequency, active cancellation is maybe the better approach.

For absorption this makes sense. From what I've seen there are things that diffuse as effectively as things a few times their thickness.

Even with absorption though, aren't anechoic chambers relying on the geometry a lot? Instead of sound bouncing between pyramid structures a metamaterial could perhaps direct it down dozens of feet microscopic holes wound up to not be several feet long.

 

[Lambda]

For absorption this makes sense. From what I've seen there are things that diffuse as effectively as things a few times their thickness.

Its a bit like with a fresnel lens. you can make it Thin but you cant make a Small lenses have big aperture.
So for your low frequency some amount of energy will just bend around your structure.

But for absorbion, transmission and reflection your right. the thickens is not necessarily directly related to the frequency

 

[NTK]

Listen to what Peter D'Antonio said at ~42:30 in this video.

 

[pozz]

Right now acoustic metamaterials are mostly used in commercial noise control applications. It'll take some time before we see them in studio treatments.

 

[alex-z]

The term metamaterial has been subverted to just mean creating multiple resonating chambers to cover a large bandwidth. While effective, it might never go mainstream IMO. Traditional absorption panels using mineral wool or fibreglass can reach as low as $2 per square foot.

As for the LS50 Meta, it seems that a good portion of the improvement actually came from the crossover tweaks. The driver and cabinet improvements contributed for sure, but 3-4 parametric EQ filters on the original LS50 will get you close to the LS50 Meta.