paper: "Ultrathin Acoustic Metasurface-Based Schroeder Diffuser"

[stevenswall]

My comments in bold below.

I can respect the effort. Feel free to show me companies working on this. I'd love to see a paper on a company rather than a college continuing and advancing this kind of work.

Needing candles is not the point, needing light and candles being inefficient and archaic is the point. Substitute earlier light bulbs as needed until the point makes sense.

I'm glad that advancements have been made in measuring acoustics.

My post was edited to include diffusion, but it duplicated and I removed it. Feel free to point me towards any companies building metasurface diffusion products or working on it.

To restate my problem: "Many [more expensive speakers] have issues that $100 computer speakers don't have."

No, I have not found even one speaker that meets my needs (sounds better in every audible and measurable way) with the above criteria and compared to a $250 DIY kit.

The LSR series is a nearfield monitor, and even midfield or further, I can hear the hiss with nothing plugged in (I put them in corners of my room, 6-8 feet away), and removing ground plugs or bringing speakers to a friend's studio with all balanced connections and power conditioning has not made a difference.

The Genelec 8260 has a waveguide and a coaxial driver, and when you limit the excursion of the midrange driver/make a three way speaker, the doppler effect doesn't affect the frequency response in any meaningful way as shown by measurements of that speaker. They also have a whitepaper showing the advancement of coaxial drivers and their flaws, which Genelec fixed. I consider the "ever changing waveguide" issue to be solved, just like the diffraction issue across air gaps and uneven surfaces.

I regularly use REW and a MiniDSP when I move my speakers, and want more absorption and even diffusion instead of reflections, and hopefully at some point can use a material that isn't unnecessarily thick and based on decades old designs.

 

[MrPotatoHead]

I'll admit that I didn't dive into that paper but it reminded me of an article I read recently about Nissan's efforts to design an acoustic meta-material that looks very 3D-printable... which I've tucked away to revisit someday.

https://www.carscoops.com/2020/01/n...ss-than-traditional-sound-deadening-material/

 

[stevenswall]

would a round cell perform better or worse? round speakers are bad, is a round diffuser good?

Round would minimize cavity and edge sizes. Not sure if that's desirable or not... You'd have triangular gaps of dead space too around circular holes, though I suppose you could put very small holes there or a triangle shape.

 

[stevenswall]

I'll admit that I didn't dive into that paper but it reminded me of an article I read recently about Nissan's efforts to design an acoustic meta-material that looks very 3D-printable... which I've tucked away to revisit someday.

https://www.carscoops.com/2020/01/n...ss-than-traditional-sound-deadening-material/

That looks shockingly easy to 3d print! I wonder how the rigidity of the material would affect things? Seems like something a bit soft might be better than something rigid and reflective? But then we'd be getting closer to rubber. Maybe it would partially act as a diffusor too if the honeycomb surface had some variation.

 

[MrPotatoHead]

I wonder how the rigidity of the material would affect things?

The photos in that article make it look pretty flexible. I've got some urethane that I could try but it's a fairly high durometer but I'm not sure how I'd test it either way. If I print something, I'll share what I find.

 

[Wes]

flex means it will vibrate with the noise at XX freq.

 

[Mawclaw]

I asked a few of the question and linked the thread to Dr. Jing. It will be interesting if he stops by.

 

[Hipper]

I wish I knew the scale... Learn blender and see how much it costs to print. Looks like most acoustic treatment companies have their heads in the sand and are stuck with decades old diffusion and absorption methods. You'd think they'd have a half decent employee who would look at recent developments, and a product manager would would get them out of the stone age.

A few years ago there was a company in the UK that were selling a product based on aircraft engine quietening technology. I can't find the details now but it seemed to be some sort of board with holes in it. There was a demonstration at a show that was on youtube where apparently people listened to music and then some not very large panels were put in the room and they listened again, and of course marvelled at the improved sound.

I never tried it as no measurements of what it did were available.

Whilst current technology is bulky it does work.

 

[MrPotatoHead]

When I attempted to pattern this up much larger than a couple inches, my slicer (Simplify3D) started randomly filling some of the holes. The walls are minimally thin so maybe I'll fatten them up and see if that helps...

EDIT: I'm sensitive to IP violations so please let me know if I should not be posting this.

 

[Mawclaw]

Response from the author of this paper.

-How did he and his team think of this approach? Why did they decide to pursue this work?


i think it is promising, but still there are limitations such as the frequency bandwidth
also we have not measured the sound absorption (we have only done some simulations )
we need to make sure that these diffusers are not highly absorptive
our motivation is simple, the conventional sound diffusers are too thick at low frequencies
any approach that can reduce the thickness would be helpful


-Is <1kHz practical with this technology? What the lower frequency limit would be?


yes, it would be very practical
we did higher frequencies in our study because they were easier to measure for us
the goal is actually to apply this technology to very low frequencies
i don't think there is a lower frequency limit, at least not theoretically



-Is true broadband diffusion possible? How linear would it be across the spectrum? Are they able to control linearity?


depending on how you define broadband, 1 octave band? 2 octave bands?
it is very challenging to design a broadband and linear spectrum
i have not seen such a design yet
but if there was one, it would be from RPG
https://www.rpgacoustic.com/



-Has he considered how to deal with lobing/periodicity effects when placing many of the same diffuser side-by-side?


this is something i am aware of , but we did not consider this in our study due to the limitation on our experimental platform
one way to reduce the lobing is to completely randomize the pattern of the diffuser


-For absorption only, what is the effectiveness of this technology? Can it be used for linear absorption <500Hz? <100Hz?


i am hoping this one would not be absorptive ....
if you want to have absorption, you have to redesign these panels
this is something we are working on right now and we have some very promising results
the results will be published later this year

 

[headshake]

@Mawclaw Thanks for asking and that was nice of the author.

-For absorption only, what is the effectiveness of this technology? Can it be used for linear absorption <500Hz? <100Hz?


i am hoping this one would not be absorptive ....
if you want to have absorption, you have to redesign these panels
this is something we are working on right now and we have some very promising results
the results will be published later this year

Good to know. The gik acoustics has a diffuser board sandwiched between two absorption panels. So maybe I make an open face diffusion + absorption panel sandwich?

some more designs for reference:
https://www.rdacoustic.cz/en/high-end-audio/hybrid-acoustic-diffuser-had-cgd-1/

https://www.monoandstereo.com/p/reference-system.html

tons of info:
https://www.rdacoustic.cz/en/blog/2019/03/30/acoustics-theory-sound-behaviour-in-closed-space/

 

[pozz]

Response from the author of this paper.

-How did he and his team think of this approach? Why did they decide to pursue this work?


i think it is promising, but still there are limitations such as the frequency bandwidth
also we have not measured the sound absorption (we have only done some simulations )
we need to make sure that these diffusers are not highly absorptive
our motivation is simple, the conventional sound diffusers are too thick at low frequencies
any approach that can reduce the thickness would be helpful


-Is <1kHz practical with this technology? What the lower frequency limit would be?


yes, it would be very practical
we did higher frequencies in our study because they were easier to measure for us
the goal is actually to apply this technology to very low frequencies
i don't think there is a lower frequency limit, at least not theoretically



-Is true broadband diffusion possible? How linear would it be across the spectrum? Are they able to control linearity?


depending on how you define broadband, 1 octave band? 2 octave bands?
it is very challenging to design a broadband and linear spectrum
i have not seen such a design yet
but if there was one, it would be from RPG
https://www.rpgacoustic.com/



-Has he considered how to deal with lobing/periodicity effects when placing many of the same diffuser side-by-side?


this is something i am aware of , but we did not consider this in our study due to the limitation on our experimental platform
one way to reduce the lobing is to completely randomize the pattern of the diffuser


-For absorption only, what is the effectiveness of this technology? Can it be used for linear absorption <500Hz? <100Hz?


i am hoping this one would not be absorptive ....
if you want to have absorption, you have to redesign these panels
this is something we are working on right now and we have some very promising results
the results will be published later this year

Thank you @Mawclaw. I've just gotten to reading these responses now.

I hope Dr. Jing comes back to us with more information later.