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This idea has been rolling around my head for almost three years, and after a lot of planning, procrastinating and planning again, I finally got off my butt and started building Leanfractal (A1-Frac) diffuser panels, designed by Tim Perry of arqen.com. I’m now done with the hard part (cutting of 64 strips of MDF and 12 pieces of ply, and routing of the fractal strips) and have only sanding and final assembly left to do. Here is a mock assembly (no glue yet) of one of the panels:

IMG_0485-3.thumb.jpeg.4d200fc896f339a5e7ccd62c0ad73059.jpeg

 

The panels are 400x1200mm, I’m making six of them. They will go on the side walls at the first reflection points, three on each side.

 

 

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Crap. That looks like a lot of work.  But looks fantastic. I’ll be interested to hear the results from you when installed 

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40 minutes ago, Bill125812 said:

Crap. That looks like a lot of work.

 

With a proper workshop (table saw, work bench, router table) this would be a cinch, and done in no time. Alas, I only had a track saw and a plunge router (from world renowned tool brands Ozito and WorkZone 😆), and an old door blade on saw horses as work bench. That made it more work than it should have been.

 

Anyway, I’m looking forward to mounting the panels on the walls, and I’m expecting nothing short of a dramatic improvement :) 

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I’ve been really wanting to try build the deep well QRD panels - I prefer the framed appearance. However, the skyline diffuser would be much simpler to construct, one size of timber cut to different lengths... 

 

This looks impressive (and time consuming!) though :) 

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A very impressive project Steffen, just to router the fractal strips alone is a rather onerous job and I see you've used the basic 7 step version ( 0,40,50,30,50,40, 0mm height) - I did the same - amazingly effective. 

 

I made the plain/simple Arqen 'leanfusers' with 60mm flats using plywood, etc but didn't keep the grain of the ply consistent and used average quality ply so they ended up looking a bit 'basic' even after stained and sealed -  I made the 2 of the 7 unit diffuser (2940 wide and 1200 high) for across the front wall behind the speakers and they do work very well  - it surprised me how heavy they ended up.

 

I had one of our local styrene companies program their computer to cut both the basic and the fractal versions of the leanfusers (apparently just 'slightly' different to avoid copyright, or something) and they made them from medium density styrene similar to the material used on houses -  they are the basic 420mm wide X 1200 high sections for both versions.

 

 I found it better to seal the porous styrene faces with heavy coating of paint  but it isn't absolutely necessary as some absorbtion is often beneficial

I glued the styrene panels to 12mm backing ply panel for portable mounting as I can't "affix" (!) them to the walls but it would be simple to attach hooks, etc  for wall 'hanging' like picture frames - unlike absorbers, these don't need any gap away from the walls to function properly.

 

To build the 'standard' 1D Schroeder diffusers with the fins/wells construction is one big PIA but much, much easier than doing a 2D diffuser,  (known as the 'Skyline') with timber, or any sort of blocks.   I did this just the once!
However, it is possible to make a 'hot knife' cutting bench and cut the different profile strips to glue together a skyline diffuser but is still quite a lot of work.  One design calls for 12 vertical 'strips' of  a 13 'block' profile and just glue all these together sideways - surprisingly, these profiles are repeated so you only need 6 different profiles and it is quite manageable with 480 x 520mm individual modules - but it's still quite a bit of 'mucking about'. 

 

The'U-tube' about the guys making them by hand doesn't mention the skill and practice these guys have developed to seem so casual about cutting the individual wells out of a solid styrene block - I tried this and created a miserable mess!

 

 The unfortunate thing about the Skylines and the Schroeder diffusers is that you need quite a few of them together to work effectively and as the commercially available ones are still about  $100/panel (usually about 500 - 600mm square) this soon adds up to considerable sum for one simple 3 x 3wall panel, or 4 x 4 one - you can imagine the cost of full wall coverings that you see sometimes in 'pro-studios'. 

 

To position any diffusers at first reflection points will effect the sound a lot  - a somewhat different effect to using absorbtion at the same point.

 

   ...   my 2 cents

 

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Ah yes, I explored many of these options myself during the past three years. There is (or used to be) actually a place in Latvia that sells all kinds of polystyrene diffuser profiles (incl. skyline and Arqen look-alikes), but they get pretty expensive by the time you get enough coverage (from memory, well over $100 for 1200x400). Local manufacture seemed even pricier.

 

I also looked at the DYI skyline option. There are several online calculators available that let you explore different depths and cell sizes, and predict the efficiency. In the end, if made from DAR timber, it would have been very expensive and heavy, and made from MDF it would have been super heavy. I may still get some polystyrene skyline diffusers for the ceiling, but on a wall I reckon the 1D stripey ones look better. The way they can be made partly hollow saves a fair bit of weight.

 

I even considered making combined absorber-diffusers (let them absorb what they can, and diffuse the rest) from 9mm acoustic pinboard, using the Arqen design. I didn’t like my chances of cutting that pinboard cleanly, though. The outcome wasn’t very clear, either. Also, my room has all the absorption it needs – large floor-to-ceiling corner absorbers, front wall absorbers, panels around the listening positions and some more stuff in the back corners. For the side walls I wanted diffusion, to curb first reflections but retain ambience.

 

The routing of the fractal strips was actually one of the easier steps. The grooves are the width of a router bit, and I made a little jig with the plunge router on top, that I just fed the strips through. Cutting the sheets into strips with the track saw was more arduous. 

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I got a sample from the guys in Latvia when they were cheap - they are okay but, as you say, quickly add up to considerable amount.

The local option surprised me in that it cost A$100 for a program setup fee (just the once) for plain and fractal version, then a further $200 for a dozen panels, mostly the 1200 X 420mm wide size and this will be same cost in future - apparently, it's a simple job for the foam cutters.

I looked around for high density styrene foam but couldn't find anyone providing cutting service, or retail sales of 'sheet form' at all but the much of absorbtion of the styrene is reduced by the heavy paint and the addition of the plywood backing makes is a 'more solid' panel - they seem to work as well, if not better, than the standard Schroeder units and a lot simpler/cheaper.

 

I did consider getting some of the different thickn 'sign-board' material to see if that would work too (10 & 20mm thickness) but haven't got around to that yet - the cutting of the sheets requires a very fine blade in the saw but not a real problem and simple PVA glue works just fine

 

I enquired in China about producing a similar profile to your routed shape but in plastic - not a problem if you pay for a die and purchaee about a km of material - even cut into 1200mm lengths, this is a lot of fractal diffusors!

 

 I was quite surprised to see that the idea of these rather simple diffusers just hasn't "caught-on" at all and the benefits of diffusion are mostly ignored in the hifi world.

 

I have a heavy duty router so might try this idea of yours myself - did you use MDF for the fractal strips or a soft wood material like pine or something  and what dia router bit did you use?

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I used MDF for most of the parts (except the plywood sheets and the meranti DAR spacers). Mainly because it was the most cost effective option.

 

The router bit is 8mm. Of course that means the fractal strips are 40mm wide, making the unit width of the panel 56mm, and the panel 392mm overall (instead of 400mm). I thought that was close enough. I didn’t like idea of having to use multiple router passes for each cut. The fractal strips are 12mm MDF, so the router cuts are 2.4mm and 4.8mm deep, respectively. That was easily done with single passes and a reasonably cheap bit.

 

Where did you get the quotation for polystyrene cutting? I suppose it’s for endless profiles (i.e. not things like skyline diffusers)?

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I somehow have started getting blue writing on the Stereonet pages that don't allow posting and is bloody weird - have to find the internet site again - I wonder what's going on?

 

Okay, basic 8mm and I don't think any measurable differences between the "original"  60mm, and this new 56mm considering the benefits of the fractal profile.

 

The local Styrene people here are called "Foam Fabrications Pty Ltd" and contact is Stuart Lown - they're in Rowville here in Melb but pretty sure you'll have a local styrene company up your way that'll do the same thing with a compatible computer access to directly load the diffuser profile into their system and reduce that 'set-up' fee.

Yes, they just cut the profile from the 1200mm block and then further cut some of those in half - it's just a commercial version of the 'hot-knife' system with computer control.

 

You could do the same thing with the Skylines but each vertical slice would be 1200mm thick 'block' and then have them cut these into 40mm thick strips - there are only really 6 different profiles in the basic 2D skyline that are repeated over the 12 or maybe 13 wells so you'd only need 6 different 'blocks', sliced to the same thickness and simply glued together - there will be a couple of zero well depths in there so you'd need a setup frame to assemble the strips with the gaps but not particularly tricky.

 

There is some differences of opinion and design about the number of wells that makeup the typical Skyline - the one I looked to has 13 vertical 'blocks' of 40mm square (ie 40mm thick piece of styrene) at the different heights, each step (or well) is also 40mm wide, to make a 520mm long strip).

 

There are 12 of these side-by-side strips assembled in specific order, each with it's 13 X 40mm square ends and surprisingly, there are only actually  6 different profiles so it's not as complicated as it looks.

 

The 40mm squares are designed for specific freq range so each of this designed Skyline panel will 520 x 480mm.  I think some of commercial ones are around 600mm square, probably for easier manufacture, or just different designs.

They're a real PIA to paint/seal but it's needed as the dust gets into the styrene easily and hard to keep the diffusers clean

 

i hope this is some use and thanks for posting - I've pretty much given up on trying to interest hifi people about diffusion and few people these days remember how to make the simple 'bass 'traps let alone the moreprecise resonant traps, etc and rely totally on digital control. 

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Yes, each of these 1200x400 panels weighs 10kg – not advisable for overhead mounting, but no issue on the walls.

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  • 2 weeks later...

Nicely done - I think there should be a continuous surface between the modules but not sure if it's really significant in practice.

What is something to consider is the relative distance between the sound reaching the listening position directly from the speakers and the sound coming from the diffusers - it looks like being about 3 - 4 msec or a path difference about 3 - 4 feet 

Before securing them to the wall, perhaps you would try them at either on the wall behind the speakers (about 5 feet) or on the back wall behind the listening position (also a space of over 5 feet) to achieve the recommended path delay of over 10msec   

 

To avoid the problem of side wall reflections, suggest a combination of absorber and diffuser  (abfuser) 

 

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Thank you for your feedback! 

 

The panels are mounted gap-less in projection (when seen straight-on), but I’m using depth modulation as per Arqen’s recommendation. The middle panels are 8cm off the wall. 
 

My front and back walls are already treated, I just needed something for the side wall first reflection spots. I previously used absorbers there. While this brought much focus to the soundstage it also reduced the sense of space and airiness that was there with untreated side walls. 
 

When researching this unexpected result I found various mentions of diffusion being a better choice for first reflection points, an opinion I had not previously come across. That’s the reason I’m trying the diffusers there. 
 

I’ll report shortly on how this works out. The room sounded pretty nice already, but I’m expecting some improvement. 

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  • 2 weeks later...

Time for an update :)

 

After first mounting the diffusers I thought the room sounded a little duller. That surprised me a bit, as I hadn’t planned for tonal changes. Then again, I wasn’t totally sure what to expect. After researching this a bit, it turns out that unvarnished timber (especially raw cut and routed MDF) is quite porous to certain frequencies. The panels were doing a mix of diffusion and absorption, apparently. I had planned to measure the effect in REW, but ended up jumping the gun and putting a couple of coats of hard PU varnish on. This looks much better and the room has its old tonality back – which I really wanted to keep, as it was the result of long and extensive experimentation with speaker placement and absorption treatment. So, without REW measurement, I sadly have no data to refer to.

 

The big effect of the panels is on the soundstage. My system and room were pretty good in that regard already. For me, this is one of the defining (and difficult) aspects of a good stereo system – everything else is comparatively easy to get right. So that’s where I focussed a lot of attention over the years. My soundstage was fairly deep and individual sources were placed well and stably, but mostly around the centre and to the off-stage sides. If the line of sight to a virtual sound source went through one of the speakers, that source would kind of snap forward (towards me) and latch onto the speaker. Placed further out to the sides and they were free again.

 

With the Arqen diffusers on the walls I now have a soundstage that is both deeper and more even. The speakers appear to play no role whatsoever in what is happening sonically. The virtual sources are also better defined, if the recording and mixing delivers. I have quite a few recordings that demonstrate this exceedingly well, a big favourite among them (that isn’t an audiophile sampler disc) has to be the Hagen Quartett playing Mozart’s K. 546 on DG. Stunningly holographic, the illusion of having the group play in your room is almost complete. Well recorded orchestral works (many to choose from, but I often use Denon’s single-point recording of Haydn symphonies for reference), have an astonishing depth of stage, that seems to go on forever.

 

Artificial soundstages also work better. Where sources are mixed so they appear to come from someplace in front of the speakers (towards the listener) or to the side of the listener, this works better than before. Behind the listener effects are more convincing. Chesky’s “Your Are Surrounded” sampler is a good test for that, as is Madonna’s “Immaculate Collection” disc from the 1990, mixed in analog Q-Sound, and Moodswings’ “Moodfood” from 1992.

 

I guess that wraps it up, unless anyone has any specific questions? I suppose this will have been the last of my major room modifications, for the foreseeable future anyway. I’ll focus on little tweaks here and there now, there are always small gains to be had for those who look :) But mostly it’s back to listening to music, without wondering “what if” all the time.

 

 

 

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38 minutes ago, Steffen said:

Time for an update :)

 

After first mounting the diffusers I thought the room sounded a little duller. That surprised me a bit, as I hadn’t planned for tonal changes. Then again, I wasn’t totally sure what to expect. After researching this a bit, it turns out that unvarnished timber (especially raw cut and routed MDF) is quite porous to certain frequencies. The panels were doing a mix of diffusion and absorption, apparently. I had planned to measure the effect in REW, but ended up jumping the gun and putting a couple of coats of hard PU varnish on. This looks much better and the room has its old tonality back – which I really wanted to keep, as it was the result of long and extensive experimentation with speaker placement and absorption treatment. So, without REW measurement, I sadly have no data to refer to.

 

The big effect of the panels is on the soundstage. My system and room were pretty good in that regard already. For me, this is one of the defining (and difficult) aspects of a good stereo system – everything else is comparatively easy to get right. So that’s where I focussed a lot of attention over the years. My soundstage was fairly deep and individual sources were placed well and stably, but mostly around the centre and to the off-stage sides. If the line of sight to a virtual sound source went through one of the speakers, that source would kind of snap forward (towards me) and latch onto the speaker. Placed further out to the sides and they were free again.

 

With the Arqen diffusers on the walls I now have a soundstage that is both deeper and more even. The speakers appear to play no role whatsoever in what is happening sonically. The virtual sources are also better defined, if the recording and mixing delivers. I have quite a few recordings that demonstrate this exceedingly well, a big favourite among them (that isn’t an audiophile sampler disc) has to be the Hagen Quartett playing Mozart’s K. 546 on DG. Stunningly holographic, the illusion of having the group play in your room is almost complete. Well recorded orchestral works (many to choose from, but I often use Denon’s single-point recording of Haydn symphonies for reference), have an astonishing depth of stage, that seems to go on forever.

 

Artificial soundstages also work better. Where sources are mixed so they appear to come from someplace in front of the speakers (towards the listener) or to the side of the listener, this works better than before. Behind the listener effects are more convincing. Chesky’s “Your Are Surrounded” sampler is a good test for that, as is Madonna’s “Immaculate Collection” disc from the 1990, mixed in analog Q-Sound, and Moodswings’ “Moodfood” from 1992.

 

I guess that wraps it up, unless anyone has any specific questions? I suppose this will have been the last of my major room modifications, for the foreseeable future anyway. I’ll focus on little tweaks here and there now, there are always small gains to be had for those who look :) But mostly it’s back to listening to music, without wondering “what if” all the time.

 

 

 

I did have a question about some more info on Denon's single-point recordings you refer to? Otherwise, stunning job - the diffusors make the space approach more of a 'studio' appearance IMO, which does appeal. Pics with varnish? :) 

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23 hours ago, Steffen said:

Time for an update :)

 

After first mounting the diffusers I thought the room sounded a little duller. That surprised me a bit, as I hadn’t planned for tonal changes. Then again, I wasn’t totally sure what to expect. After researching this a bit, it turns out that unvarnished timber (especially raw cut and routed MDF) is quite porous to certain frequencies. The panels were doing a mix of diffusion and absorption, apparently. I had planned to measure the effect in REW, but ended up jumping the gun and putting a couple of coats of hard PU varnish on. This looks much better and the room has its old tonality back – which I really wanted to keep, as it was the result of long and extensive experimentation with speaker placement and absorption treatment. So, without REW measurement, I sadly have no data to refer to.

 

The big effect of the panels is on the soundstage. My system and room were pretty good in that regard already. For me, this is one of the defining (and difficult) aspects of a good stereo system – everything else is comparatively easy to get right. So that’s where I focussed a lot of attention over the years. My soundstage was fairly deep and individual sources were placed well and stably, but mostly around the centre and to the off-stage sides. If the line of sight to a virtual sound source went through one of the speakers, that source would kind of snap forward (towards me) and latch onto the speaker. Placed further out to the sides and they were free again.

 

With the Arqen diffusers on the walls I now have a soundstage that is both deeper and more even. The speakers appear to play no role whatsoever in what is happening sonically. The virtual sources are also better defined, if the recording and mixing delivers. I have quite a few recordings that demonstrate this exceedingly well, a big favourite among them (that isn’t an audiophile sampler disc) has to be the Hagen Quartett playing Mozart’s K. 546 on DG. Stunningly holographic, the illusion of having the group play in your room is almost complete. Well recorded orchestral works (many to choose from, but I often use Denon’s single-point recording of Haydn symphonies for reference), have an astonishing depth of stage, that seems to go on forever.

 

Artificial soundstages also work better. Where sources are mixed so they appear to come from someplace in front of the speakers (towards the listener) or to the side of the listener, this works better than before. Behind the listener effects are more convincing. Chesky’s “Your Are Surrounded” sampler is a good test for that, as is Madonna’s “Immaculate Collection” disc from the 1990, mixed in analog Q-Sound, and Moodswings’ “Moodfood” from 1992.

 

I guess that wraps it up, unless anyone has any specific questions? I suppose this will have been the last of my major room modifications, for the foreseeable future anyway. I’ll focus on little tweaks here and there now, there are always small gains to be had for those who look :) But mostly it’s back to listening to music, without wondering “what if” all the time.

 

 

 

The description is what I've been suspecting diffusion would do for me, thank you. 

 

My side walls are currently reflective as the time delays are such that they help with space. Trials with absorption tightened an otherwise good image but something was lost.

 

Yep, amazing how unreflective some surfaces are untreated (paint, varnish). Even bare concrete needs sealing if low loss reflections are the goal. Makes a big difference in a reverberation chamber. 

Edited by DrSK
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22 hours ago, crtexcnndrm99 said:

I did have a question about some more info on Denon's single-point recordings you refer to? Otherwise, stunning job - the diffusors make the space approach more of a 'studio' appearance IMO, which does appeal. Pics with varnish? :) 

 

Denon issued four (I believe) box sets of these “single pair of microphone” recordings in the 90s. I’ve got one of them, containing 5 discs (Händel, Haydn, Berlioz,  Mahler and Shostakovich). The catalog numbers are CO-75652,3,4,5,6. All of these were also issued as “regular” recordings as far as I know, with the usual complement of spot and auxiliary microphones. 

 

The one point recordings were primarily a European (German?) issue, by the look of it. There isn’t a lot of information about them out there.

 

The varnish on the diffusers is a clear one, so it just made the timber look a bit darker. I’ll take a pic when I get a moment.

 

 

 

Edited by Steffen
tpyos
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Steffen,

Is it an optical illusion or do you have the diffusors sitting beside the speakers and an absorber at the first reflection point (If you were to put a mirror on the wall you would see the speaker)?

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17 hours ago, Pim said:

Steffen,

Is it an optical illusion or do you have the diffusors sitting beside the speakers and an absorber at the first reflection point (If you were to put a mirror on the wall you would see the speaker)?

 

The perspective in the pics is somewhat distorted. The nearest of the diffusers cover the 1st reflection spot, and the absorbers are right next to the listening position.

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  • 1 month later...

That looks great @Steffen. Yeah love a pic of Mk2 varnished 😜 I'm sure I read or saw somewhere putting an absorber on one wall and a reflector on the other alternating is a good practice. Not sure how it works  or if it works. You seem to have got the results you wanted though, good job!

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