Metasurface Schroeder Diffuser is 10 Times Thinner Than Usual

[Guest Peter the Greek]

See link for an article, really, really cool stuff. Would love to hear one. Basically about 200mm thick could theoretically diffuse down to 85hz!

 

 

 

 

More info here:

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.7.021034#

 

and:

 

https://journals.aps.org/prx/supplemental/10.1103/PhysRevX.7.021034/Supporting_Information2zyf_js-1.pdf

 

...I wish I had a need to try it

 

 

Edited October 20, 2017 by Peter the Greek

[Primare Knob]

 
...I wish I had a need to try it
 
 

Isn't need not enough to try it?


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[Guest Peter the Greek]

15 minutes ago, Primare Knob said:

 

Isn't need not enough 
 

 

Ha!...well that and time to build it

[nicholas9976]

See link for an article, really, really cool stuff. Would love to hear one. Basically about 200mm thick could theoretically diffuse down to 85hz!
 

 

 
More info here:
https://journals.aps.org/prx/abstract/10.1103/PhysRevX.7.021034#
 
and:
 
https://journals.aps.org/prx/supplemental/10.1103/PhysRevX.7.021034/Supporting_Information2zyf_js-1.pdf
 
...I wish I had a need to try it
 
 

Very interesting, I will read up on this. Doing diffusing in a thinner format than the venerable BBC-designed Quadratic Skyline Diffuser format has to be a good thing.

I had seen on another forum that there was no point diffusing below 500Hz as it wasn't localizable enough to make a difference. Has anyone seen any other info on the lower and upper frequency limits that it is worthwhile diffusing musical sound?


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[Soundscape]

Very interesting, I will read up on this. Doing diffusing in a thinner format than the venerable BBC-designed Quadratic Skyline Diffuser format has to be a good thing.

I had seen on another forum that there was no point diffusing below 500Hz as it wasn't localizable enough to make a difference. Has anyone seen any other info on the lower and upper frequency limits that it is worthwhile diffusing musical sound?


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Could it be useful to break up standing waves in the bass region?

[nicholas9976]

4 minutes ago, Dave O))) said:

Could it be useful to break up standing waves in the bass region?

I did a bit of quick reading on this today, and according to this paper the answer is - probably yes (with a number of qualifications/doubts they put in the paper, which does not have too much detail or test results)  http://eprints.whiterose.ac.uk/101635/1/angus2_postprint.pdf

[Guest Peter the Greek]

It'd be a most interesting test seeing if there was a perceivable difference with say a 100mm v 200mm version. Damn shame I no longer have a room to test it in

[steven365]

Have a look at the 3 different types of diffusers that I’m selling in classified. Make your life easier : )

[almikel]

On 11/7/2017 at 1:10 PM, steven365 said:

Have a look at the 3 different types of diffusers that I’m selling in classified. Make your life easier : )

you've suggested similar in other posts - what are you adding to the discussion other than flogging your products?

 

On 6/23/2017 at 12:02 PM, nicholas9976 said:

Very interesting, I will read up on this. Doing diffusing in a thinner format than the venerable BBC-designed Quadratic Skyline Diffuser format has to be a good thing.
 

Was Schroeder working for BBC back then?  Schroeder invented the QRD. The BBC did lots of cool stuff but to my knowledge didn't invent the QRD diffuser.

 

On 6/23/2017 at 12:02 PM, nicholas9976 said:

I had seen on another forum that there was no point diffusing below 500Hz as it wasn't localizable enough to make a difference. Has anyone seen any other info on the lower and upper frequency limits that it is worthwhile diffusing musical sound?


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There's no point diffusing below what's termed the "Schroeder" or "transition" frequency in your room. as below the "Schroeder/transition" frequency, modal behaviour takes over.

Where that transition frequency is depends on your room dimensions - in typical small rooms this is around 200 - 300Hz.

 

On 6/23/2017 at 5:58 PM, Dave O))) said:

Could it be useful to break up standing waves in the bass region?

Definitely not - room behaviour below the "transition" zone cannot be helped with diffusion...

 

Simply put "diffusion" works where sound frequencies act like light rays - travelling in straight lines and bouncing off surfaces in geometric ways - this happens at higher frequencies.

Below the "Transition Zone" in a room, there is no "direction" in a sound wave, and it pressurises or de- pressurises the room. - 

 

Standing waves still require consideration - how you choose to deal with them has multiple solutions.

 

cheers

Mike

 

 

 

 

[HdB]

That's a very clear and concise explanation!

[Guest]

19 hours ago, jrhill said:

That's a very clear and concise explanation!

Yea, Mike's an expert on room treatments and the engineering behind it

[steven365]

2 hours ago, almikel said:

you've suggested similar in other posts - what are you adding to the discussion other than flogging your products?

 

Was Schroeder working for BBC back then?  Schroeder invented the QRD. The BBC did lots of cool stuff but to my knowledge didn't invent the QRD diffuser.

 

There's no point diffusing below what's termed the "Schroeder" or "transition" frequency in your room. as below the "Schroeder/transition" frequency, modal behaviour takes over.

Where that transition frequency is depends on your room dimensions - in typical small rooms this is around 200 - 300Hz.

 

Definitely not - room behaviour below the "transition" zone cannot be helped with diffusion...

 

Simply put "diffusion" works where sound frequencies act like light rays - travelling in straight lines and bouncing off surfaces in geometric ways - this happens at higher frequencies.

Below the "Transition Zone" in a room, there is no "direction" in a sound wave, and it pressurises or de- pressurises the room. - 

 

Standing waves still require consideration - how you choose to deal with them has multiple solutions.

 

cheers

Mike

 

 

 

 

 

[steven365]

Oops, sorry for my another post just above. Fat fingers. Was just trying to delete my original post as  @almikel was clearly upset about me “flogging” my products. I’m sorry I didn’t add any value here. I’ll leave you in peace.

[HdB]

It's an interesting thing that the older hifi guys recognize what bass traps are and filter panels, hanging curtains, and the 'toy' things but are totally clueless about diffusers, room energy control, DI and intelligibility - pretty basic building blocks in any audio scene but rarely mentioned in hifi country

 

Mike, do you know anything about the "Audio-Precision' dsp preamp unit?  - it looks pretty impressive. 

[almikel]

On 11/12/2017 at 11:24 PM, jrhill said:

 

Mike, do you know anything about the "Audio-Precision' dsp preamp unit?  - it looks pretty impressive. 

sorry - no

I use DEQX for EQ

 

cheers

Mike

[almikel]

On 11/12/2017 at 6:56 PM, almikel said:

 

Below the "Transition Zone" in a room, there is no "direction" in a sound wave, and it pressurises or de- pressurises the room. - 

 

this is not correct - the smart guys on this forum were cutting me some slack...

Below the transition zone/Schroeder frequency in a room modal behaviour dominates down to the lowest room mode (longest room dimension = 1/2 wavelength), and you get peaks and troughs in sound pressure within the room based on the room dimensions - imagine dropping a pebble into a fish tank and after a few seconds you see all the reflections off the sides combining - this is how the sound behaves in the room in the modal zone.

On 6/23/2017 at 5:58 PM, Dave O))) said:

Could it be useful to break up standing waves in the bass region?

 

On 6/23/2017 at 6:37 PM, nicholas9976 said:

I did a bit of quick reading on this today, and according to this paper the answer is - probably yes (with a number of qualifications/doubts they put in the paper, which does not have too much detail or test results)  http://eprints.whiterose.ac.uk/101635/1/angus2_postprint.pdf

Theoretically putting a diffuser designed to work that low into the room should have an effect, and may be beneficial for room modes, but I expect the usual guidelines suggested by Cox and D'Antonio of minimum seating distance from a diffuser would apply (>3 wavelengths for the lowest frequency diffused) to avoid hearing "artifacts". This would be difficult to achieve in typical "small" rooms.

 

On the plus side though, assuming you were targeting modal frequencies, if you could get them far enough away from the LP to avoid the "artifacts", you would have flexible placement options, as other than "distance from the LP", it shouldn't matter much where in the room they went.

 

You need to drop below the lowest mode in the room to enter the pressure zone, where there is no direction in the sound wave, and the speakers are pressurising and de-pressurising the room. 

 

On 11/12/2017 at 7:17 PM, jrhill said:

That's a very clear and concise explanation!

just not factually correct - apologies!

On 11/12/2017 at 7:25 PM, 125dBmonster said:

Yea, Mike's an expert on room treatments and the engineering behind it

Demonstrably not!

 

cheers

Mike

[HdB]

I recon you're doing pretty well indeed even if this is a bit 'outside'

 

The idea of those metasurface diffusers is quite intriguing - obviously, the practical result will be in the applications but the theory is so attractive ...

 

I made some of Tim's Perry's design of flat surface diffusors (Arqen Audio) but haven't got serious with them yet - the styrene foam ones do seem to need quite a heavy plastic/paint layer on the surface in comparison to the heavier wooden ones - they seem to work in the same/similar way to the standard Shroedders as far as I can tell - early days 

[andyr]

On 11/12/2017 at 7:56 PM, almikel said:

 

Simply put "diffusion" works where sound frequencies act like light rays - travelling in straight lines and bouncing off surfaces in geometric ways - this happens at higher frequencies.

 

 

Mike, I'm interested in a specific reason for using a diffusion product - and would be interested in your comments on my thought process.  (Excuse the long preamble!)

 

In my last house, I had my Maggies in a nice big room - 8m x 5.1m ... with a cathedral ceiling that was 2.7m at the side (long) walls and ~5.5m in the centre.  (I forget the exact height - I specified the rake angle between the 2 ceiling panels to be 100 deg ... so that I wouldn't get the infinitely repeating reflection from floor up to one ceiling panel, across to the other - down to the floor ... and then up to the ceiling panel to repeat the reflection, that a 90 deg rake would've delivered.)

 

The room worked very well and, because of the length, I was able to have my Maggies 1.6m off the front wall - which gave me a great soundstage.  I then added a pair of DIY 'Room Tunes' - these were a commercial product from the mid 80s (I think) which didn't last long.  What they did - for Maggies, anyway - was diffuse the reflections from the front wall to the listener.

 

Anyway, a guy named Jon Risch published a DIY design on Audio Asylum - basically, each Room Tune consists of 3 lengths of 50mm plastic pipe fixed to a base so they were about 18mm apart but not quite parallel.  I made up a pair of these and found, when I placed them about 100mm off the front wall, in line with the reflection off the front wall from the ribbons to my ears ... that they greatly increased the depth of field I could hear.  Amazing - with the Room Tunes in place, you could hear the sound stage extended a long way back ... laying them down on the floor reduced the depth to no more than where the front wall was! 

 

Because of this experience, it seems to me that - for dipoles, anyway - soundstage depth can be increased by diffusing the higher frequency reflections only ... you don't need to have a thick diffusor designed for treating LFs, too?

 

Why this is important to me is that in my current (much smaller) listening room, I can only have my panels just over 900mm off the front wall - as a result, I don't experience much soundstage depth.  So I am thinking that a diffusor on the front wall which is designed to work with HFs only ... will deliver me the depth I want?

 

Do you agree?

 

 

Regards,

Andy

 

Edited November 20, 2017 by andyr

[almikel]

Hi @andyr,

This is all a bit off topic for the thread so apologies to @Peter the Greek...

 

I've had no experience with Maggies, or any other dipole speaker.

I haven't seen him here for a long time, but @gainphile has a lot of experience in dipoles, as does @aechmea , who runs Maggies also.

 

On 11/19/2017 at 4:01 PM, andyr said:

 

What they did - for Maggies, anyway - was diffuse the reflections from the front wall to the listener.

 

... that they greatly increased the depth of field I could hear.  Amazing - with the Room Tunes in place, you could hear the sound stage extended a long way back ... laying them down on the floor reduced the depth to no more than where the front wall was! 

 

Because of this experience, it seems to me that - for dipoles, anyway - soundstage depth can be increased by diffusing the higher frequency reflections only ... you don't need to have a thick diffusor designed for treating LFs, too?

 

...So I am thinking that a diffusor on the front wall which is designed to work with HFs only ... will deliver me the depth I want?

 

Do you agree?

 

I would agree that diffusion provides the most benefit above the transition zone in a room. Below the transition zone where modal behaviour takes over, you need to deal with the modes - however that may be.

 

In your case I think running some diffusion behind the speakers would assist getting your sound stage depth back, but I can't really comment on how low they need to diffuse, and hence how deep the diffusers need to be in your specific case of getting your sound stage back with your Maggies.

 

Sound Stage Depth (IMO) is something pretty rare these days with the usual approach of close miking everything during the recording process - to me Sound Stage Depth is the ability to place instruments and vocalists on a stage - singer at the front, drums at the back etc - very much captured in the recording (and not many of them due to close miking, and artificial pan-potting) - are we talking the same thing?

 

Given you're considering diffusion behind the speakers, and a lower diffusion point of say 500Hz, then provided the LP is >2m from the front wall, diffusion artifacts shouldn't be an issue (> 3 wavelengths away).

The "minimum seating distance >3 wavelengths of the lowest frequency diffused" guideline comes from Cox and D'Antonio -  these guys know diffusion - but it specifically applies to "old school" 1D and 2D QRD diffusers.

Note that "new school" diffusion, such as the Metasurface diffuser, will reduce the depth of the diffuser (a good thing), but not change the "minimum seating distance".

 

Cox and D'Antonio also invented the Binary Amplitude Diffuser (BAD) - both 1D and 2D. 

BAD diffusers don't generate the "quality" of diffusion that a QRD does, but because of that, the minimum seating distance is not as stringent.

1D BAD diffusers particularly interest me, as they're easily implemented as just slats/gaps over absorption in a random (eg an MLS sequence) pattern - but I've been too lazy to build one yet.

 

If you wanted to try "higher quality" diffusion behind your Maggies I'd recommend a 1D QRD panel behind each - expensive to purchase and relatively hard to DIY.

QRDude is an amazing free design tool for 1D and 2D QRD diffusers.

http://www.subwoofer-builder.com/qrdude.htm

This is "old school" diffusion - the Metasurface diffuser that's the topic of this thread is "new school" diffusion.

 

Given you heard a significant improvement in your old room with the DIY Room Tunes device, you could  try a simple 1D BAD panel approach behind the speakers - more diffusion than Room Tunes, but less than QRDs - BAD panels are also "old school" diffusion, but newer than QRDs.

 

How wide you need to go depends on the rear radiation pattern of the Maggies - but given 1D BAD panels don't diffuse as well as 1D QRDs, I would go wider with BAD panels.

The full width of the front wall in an MLS sequence BAD panel would look very cool, but I'd experiment with some smaller panels first.

 

cheers

Mike

 

 

 

[andyr]

21 minutes ago, almikel said:

Hi @andyr,

This is all a bit off topic for the thread so apologies to @Peter the Greek...

 

I've had no experience with Maggies, or any other dipole speaker.

I haven't seen him here for a long time, but @gainphile has a lot of experience in dipoles, as does @aechmea , who runs Maggies also.

 

I would agree that diffusion provides the most benefit above the transition zone in a room. Below the transition zone where modal behaviour takes over, you need to deal with the modes - however that may be.

 

In your case I think running some diffusion behind the speakers would assist getting your sound stage depth back, but I can't really comment on how low they need to diffuse, and hence how deep the diffusers need to be in your specific case of getting your sound stage back with your Maggies.

 

Sound Stage Depth (IMO) is something pretty rare these days with the usual approach of close miking everything during the recording process - to me Sound Stage Depth is the ability to place instruments and vocalists on a stage - singer at the front, drums at the back etc - very much captured in the recording (and not many of them due to close miking, and artificial pan-potting) - are we talking the same thing?

 

Given you're considering diffusion behind the speakers, and a lower diffusion point of say 500Hz, then provided the LP is >2m from the front wall, diffusion artifacts shouldn't be an issue (> 3 wavelengths away).

The "minimum seating distance >3 wavelengths of the lowest frequency diffused" guideline comes from Cox and D'Antonio -  these guys know diffusion - but it specifically applies to "old school" 1D and 2D QRD diffusers.

Note that "new school" diffusion, such as the Metasurface diffuser, will reduce the depth of the diffuser (a good thing), but not change the "minimum seating distance".

 

Cox and D'Antonio also invented the Binary Amplitude Diffuser (BAD) - both 1D and 2D. 

BAD diffusers don't generate the "quality" of diffusion that a QRD does, but because of that, the minimum seating distance is not as stringent.

1D BAD diffusers particularly interest me, as they're easily implemented as just slats/gaps over absorption in a random (eg an MLS sequence) pattern - but I've been too lazy to build one yet.

 

If you wanted to try "higher quality" diffusion behind your Maggies I'd recommend a 1D QRD panel behind each - expensive to purchase and relatively hard to DIY.

QRDude is an amazing free design tool for 1D and 2D QRD diffusers.

http://www.subwoofer-builder.com/qrdude.htm

This is "old school" diffusion - the Metasurface diffuser that's the topic of this thread is "new school" diffusion.

 

Given you heard a significant improvement in your old room with the DIY Room Tunes device, you could  try a simple 1D BAD panel approach behind the speakers - more diffusion than Room Tunes, but less than QRDs - BAD panels are also "old school" diffusion, but newer than QRDs.

 

How wide you need to go depends on the rear radiation pattern of the Maggies - but given 1D BAD panels don't diffuse as well as 1D QRDs, I would go wider with BAD panels.

The full width of the front wall in an MLS sequence BAD panel would look very cool, but I'd experiment with some smaller panels first.

 

cheers

Mike

 

 

Thanks, Mike - I shall reflect on what you've suggested.

 

 

Regrads,

Andy

 

[andyr]

On ‎21‎/‎11‎/‎2017 at 10:06 PM, almikel said:

 

Sound Stage Depth (IMO) is something pretty rare these days with the usual approach of close miking everything during the recording process - to me Sound Stage Depth is the ability to place instruments and vocalists on a stage - singer at the front, drums at the back etc - very much captured in the recording (and not many of them due to close miking, and artificial pan-potting) - are we talking the same thing?

Yes we are (talking about the same thing) but I've experienced much more depth with orchestral recordings (not close-miked, obviously!) and live recordings like The Eagles 'HFOT'.  At my last place, the audience clapping and cheers before and after "HC" extended way into the distance when the Room Tunes were up.  That's what I'm trying to reproduce. 

 

On ‎21‎/‎11‎/‎2017 at 10:06 PM, almikel said:

 

Given you're considering diffusion behind the speakers, and a lower diffusion point of say 500Hz, then provided the LP is >2m from the front wall, diffusion artifacts shouldn't be an issue (> 3 wavelengths away).

The "minimum seating distance >3 wavelengths of the lowest frequency diffused" guideline comes from Cox and D'Antonio -  these guys know diffusion - but it specifically applies to "old school" 1D and 2D QRD diffusers.

 

Thanks for that - my LP is about 2.8m from the front wall.

 

Andy

 

[almikel]

I'd try some 1D BAD diffusers behind the speakers, as below their diffusion point, they'll still be absorbing.

 

cheers

Mike